CHEMISTRY

Is a science, the object of which is to determine the constituents of bodies, and the laws which regulate the combinations of the elementary particles of matter. As an art, it has made very considerable progress. The methods of separating the constituents of bodies from each other, and of determining their properties, have been investigated with great success. But as a science, chemistry is still in its infancy; very little being known of the laws which regulate the combinations and separations of the simple substances.

Our object in the following article will be to give as clear and concise a view as possible of the present state of chemistry in all its different branches. We shall in the first place, however, lay before our readers a sketch of the history of the science, constituting, as it does, one of the most remarkable examples of the aberrations of the human intellect, and exhibiting an example of much important information, resulting from a pursuit at first both frivolous and absurd.

HISTORY.

The word Chemistry (in Greek γr i μιnT) first occurs in Suidas, a Greek writer who is supposed to have lived in the eleventh century, and to have written his lexico during the reign of Alexius Comnenus. The term indeed is said to occur in various Greek manuscripts deposited in the libraries of Rome, Venice, and Paris, and written between the fifth and eleventh centuries; but as these manuscripts have never been printed, nor their exact date determined, nothing positive can be stated on the subject.

Chemistry, as understood by Suidas, was the art of preparing gold and silver. He assures us that this art was known before the time of Diocletian. He even affirms that the golden fleece, in search of which Jason and the Argonauts went to Colchis, was nothing else than a treatise on the art of making gold, written on skins. The Argonautic expedition is commonly believed to have been made as early as one thousand two hundred and twenty-five years before the beginning of the Christian era, As early, therefore, in the opinion of Suidas, was chemistry, or the art of making gold, studied and known.

This opinion of the antiquity of chemistry was zealously supported by Olaus Borrichius, and almost the whole body of alchymistical writers. The generally received opinion among them was, that chemistry originated in Egypt; and the honour of the invention has been unanimously conferred on Hermes Trismegistus. He is by some supposed to be the same person with Chanaan, the son of Ham, whose son Mizraim first occupied and peopled Egypt. Plutarch informs us that Egypt was sometimes called Chernia. This name is supposed to be derived from Chanaan. Hence it was inferred that Chanaan was the inventor of chemistry, to which he affixed his own name. Whether the Hermes of the Greeks was Chanaan, -or his son Mizraim, it is impossible to decide; but to Hermes is assigned the invention of chemistry, or the art of making gold, by almost the unanimous consent of the adepts.

According to Albertus Magnus, “Alexander the Great discovered the sepulchre of Hermes in one of his journeys, full of all treasures, not metallic, but golden, written on a table of zatadi, which others call emerald” This passage occurs in a tract of Albertus Magnus, De Secretis Chemins, which is considered as supposititious. Nothing is said of the source whence the information contained in this passage is drawn; but, from the quotations produced by Kriegsmann, it would appear that the existence of this emerald table was alluded to by Avicenna and other Arabian writers. According to them, a woman called Sarah took it from the hands of the dead body of Hermes, some ages after the flood, in a cave near Hebron. The inscription was written in the Phoenician language; but two different Latin translations were published by Kriegsmann and Gerard Dorneus. The following is a literal translation of this far-famed inscription.

1. I speak not fictitious things, but what is true and most certain.

2. What is below is like that which is above, and what is above is similar to that which is below—to accomplish the miracles of one thing.

3. And as all things were produced by the meditation of one Being, so all things were produced from this one thing by adaptation.

4. Its father is Sol, its mother Luna, the wind carried it in its belly, the earth is its nurse.

5. It is the cause of all perfection throughout the whole world.

6. The power is perfect, if it be changed into earth.

7. Separate the earth from the fire, the subtile from the gross, acting prudently and with judgment.

8. Ascend with the greatest sagacity from the earth to heaven, and then again descend to the earth, and unite together the powers of things superior and things inferior. Thus you will possess the glory of the whole world; and all obscurity will fly far away from you.

9. This thing has more fortitude than fortitude itself; because it will overcome every subtile thing, and penetrate every solid thing.

10. By it this world was formed.

11. Hence proceed wonderful things, which in this wise were established.

12. For this reason I am called Hermes Trismegistus, because I possess three parts of the philosophy of the whole world.

13. What I had to say about the operation of Sol is completed.

Such is a literal translation of the celebrated inscription of Hcrmes Trismegistus upon the emerald tablet. It is sufficiently obscure to put it in the power of commentators to affix almost any explanation to it which they choose. The two individuals who have devoted most time to elucidate this tablet are Kriegsmann and Gerard Dorneus. They both agree that it refers to the universal medium, which began to acquire celebrity soon after the time of Basil Valentine.

This exposition, which appears as probable as any, betrays the time when the inscription seems to have been really written. Had it been taken out of the hand of the dead body of Hermes by Sarah (obviously intended for the wife of Abraham), as is affirmed by Avicenna, it is not possible that Herodotus, and all the writers of antiquity, both Pagan and Christian, should have entirely overlooked it. And how could Avicenna have learned what was unknown to all those who lived nearest the time when the discovery was supposed to have been made? Had it been discovered in Egypt by Alexander the Great, would it have been unknown to Aristotle, and to all the numerous tribe of writers whom the Alexandrian school produced, not one of whom, however, makes the least allusion to it. It bears all the marks of a forgery of the fifteenth[7:6:342] century; and even the tract ascribed to Albertus Magnus, in which the tablet of Hermes is mentioned, and the discovery related, is probably also a forgery, and doubtless a forgery of the same individual who fabricated the tablet itself, in order to throw a greater air of probability upon a story which he wished to palm upon the world as true.

Chemistry, or the art of making gold, as it is defined by Suidas, must have been unknown during the classic ages of Greece and Rome, otherwise it is impossible to account for the total silence of all the Greek and Roman writers. It is most probable that it originated among the Arabians when they began to turn their attention to medicine, after the establishment of the caliphs; or, if it had previously been cultivated by the Greeks, that it was taken up by the Arabians, and reduced by them into regular form and order.

The writings of Geber (if we admit them to be genuine) constitute the oldest chemical tract in existence; and deserve to be particularly noticed, because they make üs acquainted with the state of the science during the eighth century. Geber, whose real name was Abou-Mussah-Dschafar-Al-Soli, was a Sabean of Harran, in Mesopotamia, and lived during the eighth century. His works were translated into Latin as early as the year 1529, and an English translation by Richard Russel was published in the year 1678. They consist of four tracts, distinguished by the following quaint and not very intelligible titles: 1. Of the Investigation of Search of Perfection; 2. Of the Sum of Perfection, or of the Perfect Magistery; 3. Of the Invention of Verity or Perfection; 4. Of Furnaces, &c., with a recapitulation of the author’s experiments.

The object of Geber’s work is to teach the method of making the Philosophers Stone, which he distinguishes usually by the name of Medicine of the Third Class. The whole is in general written with so much plainness, that we can understand the nature of the substances which he employed, the processes which he followed, and the greater number of the products which he obtained. We shall give the following summary of his opinions, and of the facts which he knew.

He considered all the metals as compounds of mercury and sulphur. It is evident from what he says that this notion had been adopted by his predecessors; men whom he speaks of under the title of the ancients.

The metals with which he was acquainted were gold, silver, copper, iron, tin, and lead. These are usually distinguished by him under the names of Sol, Luna, Venus, Mars, Jupiter, and Saturn. Gold and silver he considered as perfect metals; but the other four were imperfect metals. The difference between them he considered as depending partly upon the proportions of mercury and sulphur in each, and partly upon the purity or impurity of the mercury and sulphur which enters into the composition of each.

In his book on furnaces he gives a description of a furnace proper for calcining metals; and, from the fourteenth chapter of the fourth part of the first book of his Sum of Perfection, it is obvious that the method of calcining or oxydizing iron, copper, tin, and lead, and also mercury and arsenic, were familiarly known to him. He gives a description of a furnace for distilling, and a pretty minute account of the glass or stone ware, or metallic aludel and alembic, by means of which the process was conducted. He was in the habit of distilling by surrounding his aludel with hot ashes, to prevent it from being broken. He was acquainted also with the water bath. The description of the distillation of many bodies occurs in his work; but there is not the least evidence that he was acquainted with ardent spirits. The term spirit, indeed, frequently occurs in his writings; but it was applied to volatile bodies in general, and in particular to sulphur and white arsenic, which he considered as substances very similar in their properties. Mercury also he considered as a spirit. The method of distilling per descensum, as is practised in the smelting of zinc, was also known to him. He describes an apparatus for the purpose,'and gives several examples of such distillation in his writings.

He gives also a description of a furnace for smelting metals, and mentions the vessels in which such processes were conducted. He was acquainted with crucibles, and even describes the mode of making cupels nearly similar to those used at present. The process of cupellating gold and silver, and purifying them by means of lead, is given by him pretty minutely and accurately. He called it einc-ritium ; at least that is the term employed by the Latin translator.

He was in the habit of dissolving salts in water and acetic acid, and even the metals in different menstrua. Of these menstrua he nowhere gives an account; but from our knowledge of the properties of the different metals, and from some processes which he notices, it is easy to perceive what his solvents must have been; namely, the mineral acids, which were known to him, and to which there is no allusion whatever in any preceding writer that we have seen. Whether he was the discoverer of these acids cannot be known; he nowhere claims the discovery. Indeed his object appears to have been to slur over these acids as much as possible, that their remarkable properties might not be suspected by the uninitiated. It was this affectation of secrecy and mystery which has deprived the earliest chemists of that credit and reputation to which they would have been justly entitled had their discoveries been made known to the public in a plain and intelligible manner.

The mode of purifying liquids by filtration, and of separating precipitates from liquids by the same means, was known to him. He called the process distillation through a filter.

Thus the greater number of chemical processes, such as they were practised in the eighteenth century, were known to Geber. When we compare his works with those of Dioscorides and Pliny, we perceive the great progress which pharmacy had made in the interval. This progress was probably due to the Arabian physician. We shall now notice the different chemical substances or preparations that were known to Geber.

He knew common salt, and was acquainted with potash and soda, at least in the state of carbonates. Potash was obtained by burning cream of tartar. Carbonate of soda he calls sagimen vitri ; and he points out how it may be made caustic by means of quicklime. Saltpetre was known to him; and Geber is the first writer in whom we find an account of this salt. Sal ammoniac would appear to have been quite common in his time, though there is no evidence that it was known during the classical ages of the Greeks and Romans. The same remark applies to alum, of which he mentions three kinds; icy alum or Rocca alum, Jamenous alum or alum of Jameni, and feather alum. The first two of these were named from the place where they were manufactured; the third kind was probably a native variety. Sulphate of iron, or copperas, in the state of crystals, was known to him, and appears to have been manufactured in his time.

Eaurachox borax is mentioned by him, but without any description by which we can know whether or not it was our borax. Sulphuric acid was obtained by him by distilling alum by a strong heat. In like manner nitric acid was obtained by him by putting into an alembic one pound of sulphate of iron of Cyprus, half a pound of saltpetre, [7:6:343] and a quarter of a pound of alum of Jameni, and distilling till every thing liquid was driven over. To the ni τ trie acid thus procured he gave the name of dissolving water. The acid thus obtained he employed to dissolve silver, and he concentrated the solution till the nitrate of silver was obtained in crystals. He was in the habit also of dissolving sal ammoniac in nitric acid, and employing the solution, which was the aqua regia of the old chemists, as a solvent for gold. There can be no doubt that he was acquainted with corrosive sublimate, cinnabar, red oxide of mercury, sulphuret of copper, black oxide of copper, metallic arsenic, and red oxide of iron.

Such is a short summary of the facts known to Geber, so far as they can be deduced from his writings. He is the only Arabian writer whose chemical works deserve to be noticed; for Avicenna, though his reputation was much higher, and though he ruled for many ages with despotic sway over the medical faculty in Europe, or at least divided the medical sceptre with Galen, is not entitled to notice as a chemist. The Arabians, however, had the merit of conveying a knowledge of pharmacy, and of chemistry as they understood it, to the inhabitants of Europe. This communication took place by the channel of Spain.

It is universally known that the kingdom of the Goths in Spain was overturned by the Saracens, who made themselves masters of the fairest portion of that peninsula, and retained it for a long period. The Mahommedan states in Spain had arrived at such a degree of prosperity in commerce, manufactures, population, and wealth, as is hardly to be credited. The three Abdalrahmans and Alhakem carried, from the eighth to the tenth century, the country subject to the caliph of Cordova to the highest degree of splendour. They protected the sciences, and governed with so much mildness, that Spain was probably never so happy under the dominion of any Christian prince. Alhakem established at Cordova an academy, which for several ages was the most celebrated in the whole world. All the Christians of Western Europe repaired to this academy in search of information. It contained in the tenth century a library of 280,000 volumes. The catalogue of this library filled no fewer than forty-four volumes. Seville, Toledo, and Murcia, had likewise their schools of science and their libraries, which retained their celebrity as long as the dominion of the Moors lasted. In the twelfth century there were seventy public libraries in that part of Spain which belonged to the Mahommedans. Cordova had produced one hundred and fifty authors, Almeria fifty-two, and Murcia sixty-two.

It was to these celebrated seats of learning that the curious flocked from all parts of Europe. Here they acquired a knowledge of Arabic, and of all the sciences prosecuted by the Maĥommedan sages. Among others, they studied the pharmacy of the Arabians, which differed from that of the Greeks and Romans by containing numerous chemical processes and chemical medicines. Chemistry, or Alchymy as the Arabians called it, became gradually known to the curious in Europe. And when the human mind, which had lain so long torpid in Europe, began to awaken towards the end of the twelfth century, writers on it gradually made their appearance. At first these were very few in number; but they multiplied by degrees, and in the fourteenth century they became very numerous. It will be sufficient here if we notice a few of the most remarkable of these votaries of alchymy; by which was understood the art of artificially making silver and gold out of the baser metals.

The first alchymist who deserves notice is Albert Groot, or Albertus Magnus as he is usually styled, a German, who was born in the year 1193, at Bollstaedt, and died in the year 1282. He studied the sciences at Padua, and afterwards taught at Cologne, and finally at Paris. He travelled through all Germany as provincial of the order of dominican monks; visited Rome, and was made bishop of Ratisbon. But his passion for science induced him to give up his bishopric, and return to a cloister at Cologne. Albertus was acquainted with all the sciences cultivated in his time. He was at once a theologian, a physician, and a man of the world. He was an astronomer and an alchymist, and even dipt into magic and necromancy. He wrote seven or eight treatises on various branches of chemistry, which still remain. There is no evidence that his knowledge surpassed that of Geber. But it is clear from his book De Philosophorum Lapide, that he was a believer in the existence of the philosophers’ stone, and in the possibility, by means of it, of transmuting the base metals into gold. In that treatise he gives the process for making the philosophers’ stone; but it is not intelligible. This is very remarkable, because every other part of his writings on chemical subjects is quite plain. It seems to have been the opinion of the adepts that it was unlawful to communicate the more recondite processes of their art to mankind in general. This is the reason why all that they have left us respecting the philosophers’ stone is written in such a manner that it is impossible to understand the nature of the processes, or the kind of substance which they succeeded in forming by these processes. It is this circumstance that renders the writings of the alchymists in general of so little value. They were laborious men, who subjected the various substances within their reach to a great variety of processes, and who must therefore occasionally have obtained results of importance. Had they related these processes with plainness and simplicity, we should have known the extent of their knowledge, and allowed them the credit due to their ingenuity and discoveries. But as they thought proper to adopt a different plan, their labours have been lost to posterity, and all their discoveries required to be discovered again.

Soon after Albertus, lived Roger Bacon, by far the most illustrious, the best informed, and the most philosophical of all the alchymists. He was born in 1214, in the county of Somerset. After studying at Oxford and in Paris, he became a friar; and devoting himself to philosophical investigations, his discoveries, notwithstanding the pains which he took to conceal them, made such a noise that he was accused of magic, and his brethren in consequence threw him into prison.

From an attentive perusal of his works, many of which have been printed, it is clear that Bacon was a great linguist, being familiar with Latin, Greek, Hebrew, and Arabic; and that he had perused the most important books at that time existing in all these languages. He was also a grammarian; he was well versed in the theory and practice of perspective; he understood the use of convex and concave glasses, and the art of making them. The camera obscura, burning glasses, and the powers of the telescope, were well known to him. He knew the great error in the Julian calendar, assigned the cause, and proposed the remedy. He understood chronology well; he was a skilful physician and an able mathematician, logician, metaphysician, and theologist. As a chemist, it is clear that he was acquainted with the mode of making gunpowder, and with the violence and noise with which it burns. But there is no evidence that he was aware of the usc to which it might be applied in propelling bullets from a gun-barrel with fatal velocity. We have evidence that gunpowder was known in China and India at a very remote period. These nations knew how to make it, and were in the habit of using it in fire-works; but they never seem to have [7:6:344] thought of the more important application of it as a moving force to propel bullets. This last was a European invention, though the individual to whom it was due seems not to be known. As Bacon was acquainted ∖vith Arabic, it is probable that he derived his knowledge of gunpowder from some eastern treatise.

Raymond Lully is said to have been a scholar and a friend of Bacon. He was a most voluminous writer, and acquired as high a reputation as any of the alchymists. According to Mutius, he was born in Majorca in the year 1235. His father was seneschal to King James I. of Aragon. In his younger day she went into the army, but afterwards held a situation in the court of his sovereign. Devoting himself to the sciences, he soon acquired a competent knowledge of Latin and Arabic. After studying in Paris, he got the degree of doctor conferred on him. He entered into the order of Minorites, and induced King James to establish a cloister of that order in Minorca. He afterwards travelled through Italy, Germany, England, Portugal, Cyprus, Armenia, and Palestine. He is said by Mutius to have died in 1315, and to have been buried in Majorca. The following epitaph is given by Olaus Borrichius, as engraven on his tomb:

Raymundus Lulli, cujus pia dogmata nulli Sunt odiosa viro, jacet hic in marmore miro Hic Μ. et CC. Cum P. caepit sine sensibus esse.

MCCC in the last line denote 1300, and P, which is the fifteenth letter of the alphabet, denotes fifteen; so that if this epitaph be genuine, it follows that his death took place in the year 1315.

The writings of Raymond Lully are so obscure that the writer of this article has repeatedly tried, but without success, to understand them. In addition to the re-agents known to Geber, he was acquainted with spirit of wine, which he denotes in his writings by the names of aqua vitae ardens and argentum vivum vegetabile. He was acquainted also with ammonia. How far this volatile alkali was known to any of his predecessors we do not know. He was acquainted with cupellated silver, and first obtained rosemary oil by distilling the plant with water. He employed a mixture of flour and white of egg spread upon a linen cloth to cement cracked glass vessels, and used other lutes for similar purposes.

Arnoldus de Villanova is said to have been born at Villeneuve, a village in Provence, about the year 1240. Olaus Borrichius assures us that in his time his posterity lived in the neighbourhood of Avignon, that he was acquainted with them, and that they were by no means destitute of chemical knowledge. He is said to have been educated at Barcelona, under John Casamila, a celebrated professor of medicine. This place he was obliged to leave in consequence of foretelling the death of Peter of Aragon. He went to Paris, and likewise travelled through Italy. He afterwards taught publicly in the university of Montpellier. His reputation as a physician became so great, that his attendance was solicited in dangerous cases by several kings, and even by the pope himself. He was skilled in all the sciences of his time, and was besides a proficient in Greek, Hebrew, and Arabic. When at Paris he studied astrology, and calculated that the end of the world would be in Ĩ335. In consequence of this he was condemned as a heretic, and obliged to leave France; but the pope protected him. He died in the year 1313, on his way to visit Pope Clement V. who lay sick at Avignon. His works are voluminous; but there is no evidence that he added any thing material to the stock of chemical knowledge derived from his predecessors.

John Isaac Hollandus, and his countryman of the same name, were either two brothers or a father and son, it is uncertain which. They were born in the village of Stolk in Holland, it is supposed in the thirteenth century. They wrote many treatises on chemistry, remarkable, considering the time when they lived, for clearness and precision, describing their processes with accuracy, and even giving figures of the instruments which they employed.

Basil Valentine is said to have been born about the year 1394. He is perhaps the most celebrated of all the alchymists, if we except Paracelsus. He was a benedictine monk at Erford, in Saxony. Much of his time seems to have been employed in the preparation of chemical medicines. It was he that first introduced antimony into medicine; and it is said, though on no good authority, that he first tried the effects of antimonial medicines upon the monks of his convent, on whom it acted with such violence, that he was led to distinguish the mineral from which these medicines had been extracted by the name of antimoine (hostile to monks). But Basil Valentine was a German, and wrote and spoke in that language. Now the German name for antimony is not antimoine, but spiess∙ glass. It was probably so named from a common shape of one of the most abundant ores of antimony, for spiess in German signifies a tpii∙ 1 The work on antimony of this chemist was published originally in German; but there is an excellent Latin translation, with a commentary, which was published at Amsterdam in the year 1671.

The alchymists just named constitute those who acquired the highest reputation, and were considered as possessed of the greatest quantity'· of knowledge of all the adepts. Many other names might be added to the list were it worth while to fill our pages with a long catalogue of names that had better be consigned to oblivion. The opinion of the alchymists was, that all the metals are compounds; that the baser metals contain the same constituents as gold, contaminated indeed with various impurities, but capable, when 'these impurities are removed or remedied, of assuming all the properties and characters of gold. The substance possessing this wonderful power they called lapis philosophorum, or philosophers stone ; and they usually describe it as a red powder, ‘having a peculiar smell. Many of them assure us that they had seen it, and many of them profess to give processes by which it could be made, though none of these processes are intelligible. They nowhere (or at least very seldom) affirm that they were in possession of this grand arcanum; but there can be no doubt, from the processes which they give, that it was their intention to induce their readers to believe that they were acquainted with it. Many stories of the transmutation of the baser metals into gold are on record, and attested by evidence that at first sight appears unimpeachable. The following relation of this kind is given by Mangetus, on the authority of M. Gros, a clergyman of Geneva, of the most unexceptionable character, and at the same time a skilful physician and expert chemist.

About the year 1650 an unknown Italian came to Geneva, and took lodgings at the sign of the Green Cross. After remaining there a day or two, he requested Deluc, the landlord, to procure him a person acquainted with Italian to accompany’· him through the town, and point out those things which deserved to be examined. 1)eluc requested Μ. Gros, at that time a student in Geneva, and about twenty years of age, to accompany the stranger. This he did during about a fortnight, at the end of which the stranger began to complain of the want of money. This rather alarmed Μ. Gros, as he was apprehensive that the stranger intended to ask the loan of money [7:6:345] from him. But instead of this the Italian asked him if he was acquainted with any goldsmith whose bellows and other utensils they might be permitted to use, and who would not refuse to supply them with ,the different articles requisite for a particular process which he wanted to perform. M. Gros named a Μ. Bureau, to whose house the ltalian immediately repaired. He readily furnished crucibles, pure tin, quicksilver, and the other things required by the Italian. The goldsmith left his workshop that the Italian might be under less restraint, leaving M. Gros with one of his own workmen as an assistant. The Italian put a quantity of tin into one crucible and a quantity of quicksilver into another. The tin was melted in the fire, and the mercury heated. It was then poured into the melted tin, and at the same time a red powder inclosed in wax was projected into the amalgam. An agitation took place, and a great deal of smoke was exhaled from the crucible; but this speedily subsided, and the whole being poured out, formed six heavy ingots having the colour of gold. The goldsmith was called in by the Italian, and requested to make a rigid examination of the smallest of these ingots. The goldsmith, not content with the touchstone and the application of aquafortis, exposed the metal on the cupel with lead, and fused it with antimony; but it sustained no loss. He found it possessed of the ductility and specific gravity of gold; and, full of admiration, he exclaimed that he had never worked before on gold so perfectly pure. The Italian made him a present of the smallest ingot as a recompense; and then, accompanied by M. Gros, he repaired to the mint, where he received from M. Bacuet, the mint master, a quantity of Spanish gold coin, equal in weight to the ingots which he had brought. To Μ. Gros he made a present of twenty pieces, on account of the attention which he had paid him. And after paying his bill at the inn, he added fifteen pieces more to serve to entertain M. Gros and M. Bureau for some days; and, in the mean time, he ordered a supper, that he might on his return have the pleasure of supping with these two gentlemen. He went out, but never returned, leaving behind him the greatest regret and admiration. It is needless to add, that M. Gros and Μ. Bureau continued to enjoy themselves at the inn till the fifteen pieces which the stranger had left were exhausted.

The preceding story, taken from the preface of Mangetus’s Bibliotheca Chemica i is as well authenticated as any alchymistical story whatever. The reader will observe that it is stated, not on the authority of a person who was the actor, but by a stranger, to whom a witness of the transmutation related it. Now this evidence, though the best that can be got, is not sufficient to authenticate so wonderful a story. .A little latent vanity might easily induce the narrator to suppress or alter some particulars, which, if known, might have stripped the narrative of every thing marvellous which it contains, and led us into the secret of the origin of this gold which the Italian is said to have transmuted from tin.

In consequence of the universality of the opinion that gold could be made by art, there was a set of impostors who went about pretending that they were in possession of the philosophers’ stone, and offering to communicate the secret of making it for a suitable reward. Nothing is more astonishing than that persons should be found credulous enough to be the dupes of such impostors. The very circumstance of their claiming a reward was a sufficient proof that they were ignorant of the secret which they pretended to reveal; for what motive could a man have for asking a reward who was in possession of a method of making gold at pleasure. Yet strange as it may appear, they met with abundance of dupes credulous enough to believe their asseverations, and to supply them with money to enable them to perform the wished-for processes. The object of these impostors was either to pocket the money thus furnished, or they made use of it to purchase various substances, from which they extracted oils, acids, or similar products, which they were enabled to sell with profit. To keep the dupes who supplied them with money in good spirits, it was necessary to show them occasionally small quantities of the baser metals transmuted into gold. This they performed in various ways.

Sometimes they made use of crucibles with a false bottom. At the real bottom they put a quantity of gold or silver. This was covered with a portion of powdered crucible glued together by gum or wax. The materials being put into the crucible, and heat applied, the false bottom disappeared, and at the end of the process the gold or silver was found at the bottom of the crucible. Sometimes they made a hole in a piece of charcoal, and filled it with oxide of gold or silver, and stopped up the hole with a little wax; or they soaked the charcoal in solutions of these metals; or they stirred the mixture in the crucible with hollow rods, containing oxide of gold or silver within, and the bottom shut with wax. By these means the gold or silver wanted was introduced during the operation, and considered as a product. Sometimes they used solutions of silver in nitric acid, or of gold in aqua regia, or an amalgam of gold or silver, which being adroitly introduced, furnished the requisite quantity of metal. A common exhibition was to dip nails into a liquid, and take them out half converted into gold. The nails were one half gold, one half iron, neatly soldered together, and the gold covered with something to conceal the colour, which the liquid was capable of removing. Sometimes they had metallic rods one half gold and one half silver, and the gold end whitened with mercury; the gold end was dipt into the transmuting liquid, and then heated. The mercury was dissipated, and the gold appeared.

The alchymists, notwithstanding the absurdity of their pursuits, contributed something towards the progress of chemistry; and when Basil Valentine restored the art to the object for which it was originally cultivated by the Arabians, namely, the preparation and improvement of medicines, it began to attract a little more of the attention of mankind. But the person who first shook the throne of Galen and Avicenna to its foundation, and who satisfied the public of the paramount importance of chemistry in medicine, and who therefore must be considered as indirectly the author of its subsequent popularity and consequent progress, was Paracelsus, of whom therefore it will be proper to give a short account here.

Philippus Aureolus Theophrastus Paracelsus Bombast ab Hohenheim, was born at Einsideln, two German miles from Zurich, where his father was a medical practitioner. After receiving the first rudiments of his education, he became a wandering scholar, as was at that time customary with poor students. He wandered from province to province, predicting the future by the position of the stars and the lines on the hand, and exhibiting all the chemical experiments which he had learned from founders and alchymists. He seems to have been for some time an army surgeon; but whether he ever enjoyed the benefit of an university education is not certain. At the age of thirty-three the great number of fortunate cures which he had performed rendered him an object of admiration to the people of Germany. He assures us that he cured eighteen princes, whose diseases had been aggravated by the practitioners devoted to the system of Galen. Among others, he cured Philip, margrave of Baden, of a dysentery, who promised him a great reward, but did not keep his promise, and even treated him in a way unworthy of that [7:6:346] prince. This cure, however, and others of a similar nature, added greatly to his celebrity; and in order to raise his reputation to the highest pitch, he announced publicly that he was able to cure all the diseases hitherto reckoned incurable; and that he had discovered an elixir by means of which the life of man might be prolonged at pleasure to any extent whatever.

In the year 1526 he was appointed professor of physic and surgery in the university of Basil, in consequence, it is said, of the recommendation of Oecolampadius. He introduced the custom of lecturing in the common language of the country, as is at present the universal practice. But during the time of Paracelsus, and long after, indeed, all lectures were delivered in Latin. The new method which he followed in explaining the theory and practice of the art, the numerous fortunate cures which he stated in confirmation of his method of treatment, the emphasis with which he spoke of his secrets for prolonging life, and for curing every kind of disease without distinction, but still more, his lecturing in a language understood by the whole population, drew to Basil an immense crowd of idle, enthusiastic, and credulous hearers.

His lectures on the practice of medicine still remain, written in a confused mixture of German and barbarous Latin, and containing little or nothing except a farrago of empirical remedies, advanced with the greatest confidence. They have a greater resemblance to a collection of quack advertisements than to the sober lectures of a professor in a university. He began his professorial career by burning publicly in his class-room, and in the presence of his pupils, the works of Galen and Avicenna, assuring his hearers that the strings of his shoes possessed more knowledge than those two celebrated physicians. All the universities united had not, he assured them, so much knowledge as was contained in his own beard; and the hairs upon his neck were better informed than all the writers that ever existed put together.

But his popularity was short lived, being destroyed not so much by the grossness of his language, as by the irregularity and immorality of his life. He hardly ever went to his class-room to deliver a lecture till he was half intoxicated, and scarcely ever dictated to his secretaries till he had lost the use of his reason by a too liberal indulgence in wine. If he was summoned to visit a patient, he scarcely ever went but in a state of intoxication. Not unfrequently he passed the whole night in the ale-house in the company of peasants, and, when morning came, was quite incapable of performing the duties of his station. Towards the end of the year 1527 a disgraceful dispute into which he entered brought his career as a professor to a sudden termination. The canon Cornelius of Lichtenfels, who had been long a martyr to the gout, employed him as a physician, and promised him one hundred florins if he could cure him. Paracelsus made him take three pills of laudanum, and having thus freed him from pain, demanded the sum agreed upon. But Lichtenfels refused to pay him the whole of it. Paracelsus summoned him before the court, and the magistrate of Basil decided that the canon was bound to pay only the regular price of the medicine administered. Irritated at this decision, our intoxicated professor uttered a most violent invective against the magistrate, who threatened to punish him for his outrageous conduct. His friends advised him to save himself by flight. He took their advise, and thus abdicated the professorship. But by this time his celebrity as a teacher had been so completely destroyed by his foolish and immoral conduct, that he had lost all his hearers. In consequence of this state of things, his flight from Basil produced no sensation whatever in that university.

He betook himself, in the first place, to Alsace, and sent for his faithful follower the bookseller Operinus, together with the whole of his chemical apparatus. In 1528 we find him at Colmar, where he commenced his ambulatory life of a theosophist, which he had led during his youth. In 1531 he was at St Gallen, in 1535 at Pfer-fersbode, and in 1536 at Augsburg. At the request of John de Leippa, marshall of Bohemia, he undertook a journey into Moravia, to cure him radically of the gout. But John de Leippa, instead of receiving benefit from his medicines, became daily worse, and at last died. This was the fate also of the lady of Zerotin, on whom the remedies of Paracelsus produced no fewer than twenty-four epileptic fits in one day. Instead of waiting the disgrace with which the death of this lady would have overwhelmed him, Paracelsus announced his intention of going to Vienna, that he might see how they would receive him in that capital. In 1538 we find him at Villach. In 1540 he was at Mindelheim, and in 1541 at Strasburg, where he died in St Stephen’s Hospital, in the forty-eighth year of his age.

When we attempt to form an accurate conception of the medical and philosophical opinions of this singular man, we find ourselves beset with almost insurmountable difficulties. His statements are so much at variance with each other in his different pieces, and so much confusion reigns with respect to the order of publication, that we know not what to fix on as his last and maturest opinions. His style is execrable, filled with new words of his own coining, and of mysticisms either introduced to excite the admiration of the ignorant, or from the fanaticism and credulity of the writer, who was to a considerable extent the dupe of his own impostures. That he was in possession of the philosophers’ stone, or of a medicine capable of prolonging life to an indefinite length, as he all along asserted, he could not himself believe. But he had boasted so long and so loudly of his wonderful cures, and of the efficacy of his medicines, that he seems ultimately to have placed implicit faith in them.

His obscurity may have been partly the effect of design, and may have been intended to exalt the notions entertained of his profundity. He uses common words in new significations, without giving any indication of the change which lie introduced. Thus anatomy signifies, in his writings, the nature, force, and magical designation of a thing. Paracelsus calls anatomy the knowledge of that model after which all things are created. He terms the fundamental force of a thing a star, and defines alchymy the art of drawing out the stars of metals. The star is the source of all knowledge. When we cat, we introduce into our bodies the star, which is then modified, and favours nutrition.

It is likely that many of his obscure expressions are the result of ignorance. Thus he uses the term pagoyus for paganus. He gives the name of pagoyce to the four entities or causes of disease founded on the influence of the stars, the elementary qualities, the occult qualities, and the influence of spirits, because these had been already admitted by the pagans. But the fifth entity, or cause of disease, which has God immediately for its author, is ηοη-pagoya. As is the case with all fanatics, he treated with contempt every kind of knowledge acquired by labour and application, and boasted that his wisdom was communicated to him directly by God Almighty. From a careful inspection of his works, it appears pretty plain that he was both a fanatic and an impostor, and that his theory (if such a name can be given to the reveries of a drunkard) consisted in uniting medicine with the doctrines of the cabala.

He continually cries up the importance of chemical medicines[7:6:347], and condemns with great violence and coarseness of language the Galenical remedies employed by the physicians of his time. It was this circumstance that made chemical preparations become fashionable among medical men. It was this that drew the attention of apothecaries and physicians to chemical medicines, and occasioned those numerous investigations which contributed so essentially to the improvement and progress of chemistry as a science. He himself employed mercurial preparations without scruple in the cure of the venereal disease. And his success was such as to add greatly to his medical reputation. There is no reason for believing that the use of mercury in this disease was a contrivance of Paracelsus. It is generally admitted that it was first tried for that disease by Carpus of Bologna, and that it was to that Italian physician that Paracelsus was indebted for his knowledge of this most important medicine. Paracelsus seems to have been the first who employed opium freely; and he relied upon it to remove not merely pain, but to cure several acute diseases. It would seem to have been his remedy for gold, and even for fever. Nothing is known respecting the source from which he derived his knowledge of this powerful medicine. His reputation as a chemist does not depend on any discoveries which he actually made, but upon the great importance which he attached to the knowledge of it, and to his making an acquaintance with chemistry an indispensable requisite of a medical education.

Paracelsus had many followers, who cried up chemical remedies to the skies, and ridiculed the inert medicines of the Galenists. This led to a violent controversy, especially in France, where the opinions of Paracelsus were zealously supported by Joseph du Chesne, better known by the name of Quercitanus, who was physician to Henry IV. He was opposed by Riolanus, who attacked chemical remedies with much bitterness. The medical faculty of Paris took up the cause of the Galenists, and prohibited their fellows and licentiates from using any chemical medicine whatever. Fenot affirmed that gold possesses no medicinal properties whatever, that crabs’ eyes are of no use when administered internally, and that the laudanum of Paracelsus (being an opiate) is in reality hurtful instead of being beneficial. The decree of the medical faculty of Paris, which placed antimony among the poisons, was followed by that of the parliament of Paris, strictly prohibiting the internal administration of any preparation of that metal. In 1603 the celebrated Theodore Turguet de Mayenne was prosecuted, because, in spite of the prohibition, he continued to sell antimonial preparations. The decree of the faculty against him exhibits a remarkable proof of the bigotry and intolerance of the times. Yet Turguet does not seem to have been molested in consequence of this decree. He ceased indeed to be professor of chemistry, but continued to practise medicine as formerly. At last he went to England, whither he had been invited to accept an honourable appointment.

The mystical doctrines of Paracelsus arc supposed to have given origin to the sect of the Rosicrucians ; but the probability is that no such sect ever existed. The notion of their existence seems to have been owing to a ludicrous performance of Valentine Andreae, an ecclesiastic of Calwe, in the country of Wirtemburg. A crowd of enthusiasts swallowed his fictitious statements as true, and endeavoured to unite the followers of the rosa crux into a sect. According to them, every thing is accomplished, provided only we possess sufficient faith. “To fly in the air, to transmute metals, and to know all the sciences, nothing more is requisite than faith.” Oswald Crollius, physician to the Emperor Rodolph II. must take his station among these enthusiasts. His opinions were refuted by Andrew Libavius of Halle in Saxony, one of the most enlightened men, and one of the most successful chemists, of the time. The bichloride of tin, which he first formed, still goes by the name of fuming liquor of Libavius. His system of chemistry, published at Frankfort in 1595, is really an excellent book, and deserves the attention of every person who is interested in the history of chemistry.

Libavius found, in Angelus Sala of Vicenza, a successor worthy of his enlightened views and indefatigable exertions to oppose the torrent of fanaticism which threatened to overwhelm all Europe. Sala was still more addicted to chemical remedies than Libavius himself; but he had abjured a multitude of prejudices which had distinguished the school of Paracelsus. He discarded po tabile, and considered fulminating gold as the only medicine of that metal which deserved to be prescribed. He first ascertained the constituents of sal ammoniac. To him, therefore, we are indebted for the first accurate notion of ammonia.

But chemistry was destined speedily to undergo a new revolution, which shook the Spagirical system to its foundation, substituted other principles, and gave to medicine an aspect entirely new. This revolution was in some measure due to the labours of Van Helmont.

John Baptist Van Helmont was a gentleman of Brabant. Born in Brussels in 1577, he studied scholastic philosophy at Louvain till the age of seventeen. He next associated himself to the Jesuits, who then delivered courses of philosophy at Louvain, to the great displeasure of the professors of that city. But Van Helmont was disappointed of the knowledge that he expected from them. Nor was he better satisfied with the doctrine of the Stoics. At last the works of Thomas a Kempis, and of John Tau-lcrus,. fell into his hands. These sacred books of mysticism attracted his attention. He perceived that wisdom is the gift of the Supreme Being; that it must be obtained by prayer; and that we must renounce our own will, if we wish to participate in the influence of the divine grace. From this moment he imitated Jesus Christ in his humility. He abandoned his property to his sister, and renounced his rank in society. It was not long before he reaped the fruit of these abnegations. A genius appeared to him in all the important circumstances of his life. In the year 1633 his own soul appeared to him under the figure of a resplendent crystal. His desire of imitating Christ induced him to study medicine. He made himself master of the works of Hippocrates and Galen. But as his taste for mysticism was insatiable, he soon became disgusted with the writings of the Greeks. An accident led him to abandon them for ever. Happening to take up the glove of a young girl affected with the itch, he caught that disagreeable disease. The Galenists whom he consulted attributed it to the combustion of the bile, and the saline state of the phlegm. They prescribed a course of purgatives, which weakened him considerably, without producing a cure. This led him to form the plan of reforming medicine. He first studied the works of Paracelsus; but could not avoid despising the disgusting egotism and the ridiculous ignorance of that fanatic. He took the degree of doctor of medicine in 1599. After travelling through France and Italy, he married a rich ßrabantine lady, by whom he had several children. He died in the year 1644, in the sixty-seventh year of his age. His works were published after his death by his son Mercurius. As a medical man he must be considered as a great improver on the miserable system of practice at that time followed. As a chemist he is far from being without merit. To him we are indebted for the invention, or at least the first application, of the term gas, in the sense in which it is employed by modern chemists. He was aware that gas was [7:6:348] extricated in abundance during the application of heat to various bodies, and during the solution of various carbonates and metals in acids. His theory of the formation of urinary calculus does him great credit, and constituted a first step towards the elucidation of that important portion of physiology. He satisfied himself that these calculi differ completely from common stones, and that they do not exist in the food or drink. Tartar, he says, precipitates from urine, not as an earth, but as a crystallized salt. In like manner, the natural salt of urine precipitates from that liquid, and gives origin to calculi. We may imitate the natural process by mixing spirit of urine with rectified alcohol. Immediately an offa alba is precipitated.

The decided preference given to chemical medicines by Van Helmont, and the uses to which he applies chemical theory, had a natural tendency to raise chemistry to a higher rank in the eyes of medical men than it had yet reached. But the man to whom the credit of founding the iatro-chemical sect is due, is Francis de la Boé Sylvius, who was born in 1614. While a practitioner of medicine at Amsterdam, he studied with profound attention the system of Van Helmont, and the rival and much more popular theory of Descartes. Upon these he founded his own theory, which contains little entitled to the name of original, notwithstanding the tone in which he speaks of it, and his repeated declarations that he had borrowed from no one. He was appointed professor of the theory and practice of medicine in the university of Leyden, where he taught with such eclat, and drew after him so great a number of pupils, that Boerhaave alone surpassed him in that respect. Every thing was explained by him according to the principles of chemistry, as at that time understood. And certainly both his physiology and his practice are absurd in an almost incredible degree. All diseases were occasioned by a superabundance of an acid or an alkali in the blood. The acid diseases were cured by the administration of an alhali, and the alkaline diseases by the administration of an acid.

It is a remarkable circumstance, and shows clearly that mankind in general had become disgusted with the dogmas of the Galenists, that iatro-chemistry was adopted more or less completely by almost all physicians. And the few that opposed it combated its dogmas by arguments not less nugatory than those of the iatro-chemists themselves. The first person who really shook the pillars on which this sect rested their opinions was Mr Boyle. This he did in 1661, by the publication of his Sceptical Chemist. His arguments did not indeed immediately put an end to the sect, but they served somewhat to shake the confidence with which they supported their peculiar -opinions. These opinions were successfully refuted by the celebrated Dr Archibald Pitcairn of Edinburgh; and they finally disappeared, being unable to stand their ground against the unrivalled celebrity of Boerhaave.

Herman Boerhaave possesses so much merit as a chemist, that his name cannot be omitted in this sketch. He was born at Voorhout, a village near Leyden, in 1688, where his father was parish clergyman. At the age of sixteen he was left an orphan, without protection, advice, or fortune. He had already studied theology and the kindred sciences, and meant to offer himself as a clergyman; but being accused of leaning towards the principles of Spinoza, he was obliged to turn his attention to medicine. In 1693 he graduated and began to practise, supporting himself by teaching mathematics, till his medical fees became sufficient to support him. Meanwhile he erected a laboratory, and devoted a considerable time to the study of chemistry and of botany. On the death of Drelincourt in 1702 he was appointed professor of medicine in the university of Leyden. His reputation speedily became very high: he was successively appointed professor of botany and of chemistry, while rectorships and deanships were showered upon him with an unsparing hand.

His system of chemistry, published in two quarto volumes in 1732, and of which we have an excellent English translation by Dr Shaw, was the most learned and most luminous treatise on chemistry that the world had yet seen, being nothing less than a collection of alt the chemical facts and processes that were known in Boerhaave’s time, collected from a thousand different sources, and from writings equally disgusting for their obscurity and their mysticism. Every thing is stated in the plainest way, and chemistry is shown as a science, and an art of the first importance, not merely to medicine, but to mankind in general.

Towards the end of the seventeenth century several other chemists appeared, who contributed considerably to the increase of chemical facts, or to the improvement of chemical processes. It will be sufficient to mention the names of Glauber, the discoverer of the salt that bears his name; of Kunkel, the discoverer of phosphorus; of Lemery, who rendered the science so popular in France; and of Homberg, and the two Geoff roys, successively members of the French Academy of Sciences, and makers of important discoveries.

The first person who attempted to arrange all the known chemical facts under a theory, was John Joachim Beecher, who was born at Spires, in Germany, in the year 1635. His father was a Lutheran clergyman; but he lost him early; and as the part of Germany where he lived had been ruined by the thirty years’ war, his family was reduced to great poverty. Yet he contrived to procure a medical and chemical education. In 1666 he was appointed professor of medicine in the university of Mentz, and soon after chief physician to the elector. There he was furnished with an excellent laboratory. But he soon fell into difficulties, and was obliged to take refuge in Vienna. Thence he repaired to Holland, and settled in Haerlem. In 1680 we find him in Great Britain, where he examined the Scottish lead mines and smelting works; and in 1681 and 1682 lie traversed Cornwall, and studied the mines and smelting works of that great mining county. He died suddenly in 1682, while he was negotiating about an advantageous situation offered him by the Duke of Mecklenburg Gustrow.

His chemical theory was given to the world in his Physica Subterranea ; and it was soon after embraced and improved upon by Stahl. George Earnest Stahl was certainly one of the most remarkable men of the age in which he lived. He was born at Anspach in the year 1660. He studied medicine, and in 1694 was named, at the solicitation of Frederick Hoffmann, second professor of medicine in the university of Halle, which had just been established. It is probable that he also taught chemistry in the same university. He aimed at legislating, both in medicine and chemistry; and this aim, ambitious as it was, was in some measure successful. The chemical theory invented by Beecher, and simplified by Stahl, had for its object the explanation of combustions, and the reasons of the alterations induced by it on bodies. All combustible bodies, in their opinion, are compounds, and contain one principle in common, to which they owe their combustibility. To this principle they gave the name of phlogiston. When a body burns, the phlogiston leaves it, and occasions the appearance of the beat and the light which constitute combustion in common language. What remains is the other constituent of the body. When sulphur burns, sulphuric acid remains. Therefore sulphur is a compound [7:6:349] of sulphuric acid and phlogiston. When the metals are burnt, earthy bodies or calces remain. Hence the metals are compounds of calces and phlogiston. This theory was universally adopted by succeeding chemists, and was only overturned in consequence of the prodigious accumulation of new facts for which the Stahlian theory had not provided, towards the end of the eighteenth century.

The chemical school of Berlin, of which Stahl may in some measure be considered as the founder, has furnished an almost uninterrupted series of eminent chemists. Neumann, Pott, Eller, and Margraaf, are the most celebrated advocates of the Stahlian theory who adorned that school. During the same period a series of most meritorious men and distinguished chemists adorned the Academy of Sciences of Paris. The most deservedly celebrated of them were Reaumur, Hellot, Duhamel, Macquer, and Rouelle.

Hitherto chemistry had attracted but little attention in Great Britain, and had been cultivated chiefly as an adjunct of medicine. It was in this way that it made its way into the different universities. It was considered as a science necessary for physicians, in order to enable them to prepare chemical medicines. The first person who seems to have viewed chemistry as capable of becoming a separate and important science, equally useful to mankind as mechanics itself, and capable of raising the successful cultivator of it to a high station among men of science, was Dr William Cullen, who afterwards raised the university of Edinburgh to such celebrity as a medical school. He was born at Hamilton in 1712, and after serving an apprenticeship to a surgeon in Glasgow, he settled, when very young, at Shotts in Lanarkshire. There he accidentally formed an acquaintance with Archibald duke of Argyll, who at that time bore the chief political sway in Scotland. By his influence he was appointed lecturer on chemistry in the University of Glasgow. There he began to explain his views respecting the science; and such was his popularity, that his class soon became crowded with students. Such was his reputation as a chemist, that on Dr Plummer’s death in 1756 he was unanimously invited to fill the vacant chemical chair in the University of Edinburgh. There his popularity followed him, and continued to increase in consequence of his own admirable conduct, notwithstanding the attempts of some of his colleagues to injure him with the public. Though his appointment to the medical chair in the University of Edinburgh in the year 1766 put an end to his chemical career, yet he had the merit of drawing the attention of the public to that fascinating and most important science, and pointing out what might be done by an experimental cultivation of it. He had the merit also of being the teacher of Dr Black, and of filling that eminent chemist with a passion for the science in which he was destined to distinguish himself.

Joseph Black was born in France, on the banks of the Garonne, in the year 1758. His father was a native of Belfast, but of a Scotch family. Young Black was educated in Belfast, and in 1746 he was sent to continue his education in the University of Glasgow. It was at that time that Dr Cullen began to teach chemistry in that university. Young Black, who had made choice of medicine as his profession, naturally attended the chemical lectures. He was soon fascinated with the study, became intimate with Cullen, and soon assisted him in his experiments. He went to Edinburgh to finish his medical studies in 1751. Here he discovered the nature of the difference between limestone and quicklime. The first is a salt, a compound of carbonic acid (which he called fixed air) and lime; the second is the lime uncombined. He showed that carbonic acid is a gas possessed of the properties of air, but capable, like other acids, of combining with bases, and constituting a genus of salts to which the name of carbonates has been since given. He made this discovery the subject of his inaugural dissertation when he took his medical degree in 1756; and gave, in the same thesis, an account of his experiments on magnesia and its salts, proving it to possess properties analogous to, but quite different from, those of lime. This thesis immediately raised him to the rank of a first-rate chemist.

It was at this time that Dr Cullen was removed to Edinburgh, and in 1756 Dr Black succeeded him as lecturer on chemistry in the University of Glasgow. Here he brought to maturity his speculations respecting latent heat, which first enabled chemists to give the doctrines of heat a scientific form. In 1766 he was appointed professor of chemistry in Edinburgh. Here he continued annually to deliver an admirable course of lectures; but contributed but little afterwards to the progress of the science, except by his annual explanation of its doctrines. He died in November 1799, in the seventy-first year of his age.

The tempting career which Dr Black had opened, but which his slender stock of health unqualified him for prosecuting, was entered on by Mr Cavendish, and prosecuted with uncommon accuracy. To him we are indebted for the knowledge of the properties of carbonic acid and hydrogen gases, and for the discovery of the composition of water and of nitric acid. He first gave a rigid analysis of the air, and showed that its constituents underwent no sensible variation. To him also we are indebted for our knowledge of the freezing point of mercury. He died on the 4th of February 1810, in the seventy-ninth year of his age.

But the man who contributed the most to the rapid progress of chemistry, and to whom it is chiefly indebted for the great degree of popularity which it enjoyed towards the end of the eighteenth century, was Dr Priestley. We cannot here expatiate upon the life of this extraordinary man, which will doubtless find a place in another part of this work; but shall merely confine ourselves to an enumeration of some of the most important additions which he made to chemistry. To him we are indebted for a knowledge of the mode of preparing nitrous gas, or deutoxide of azote as it is now called, of its remarkable properties, and in particular for the use that may be made of it in analysing atmospheric air. On the 1st of August 1774 he discovered oxygen gas, by heating the red oxide of mercury, and collecting the gaseous matter given out by it. He almost immediately detected the remarkable property which it has of supporting combustion better, and animal life longer, than the same volume of common air. He first made known sulphurous acid, fluosilicic acid, muriatic acid, and ammonia, in the gaseous form, and pointed out easy methods of procuring them; he describes with exactness the most remarkable properties of each. He likewise pointed out the existence of carburetted hydrogen, though he made few experiments to determine its nature. His discovery of protoxide of azote affords a beautiful example of the advantages resulting from his method of investigation, and the sagacity which enabled him to follow out any remarkable appearance which occurred. Carbonic oxide gas was discovered by him while in America, and it was brought forward by him as·an incontrovertible refutation of the antiphlogistic theory. Though he was not the discoverer of hydrogen gas, yet his experiments on it were highly interesting, and contributed essentially to the revolution which chemistry soon after underwent. He first discovered the great increase of bulk which takes place when electric sparks are passed through ammoniacal gas, a fact which led Bcrthollet to the analysis of this gas. His experiments on the amelioration of atmospherical air by the vegetation of plants, on the oxygen gas given out by their leaves, and on the respiration[7:6:350] of animals, are not less curious and interesting. Such are the most striking of his discoveries; but his three volumes on air constitute one of the richest storehouses of chemical facts in existence. It may be said without exaggeration that Dr Priestley was one of the most diligent and successful pioneers in chemistry that ever existed. He was too rapid, and too little given to ponder over his opinions before he gave them to the world, to constitute a good philosopher; but in genius and invention he was not inferior to any of his contemporaries. Dr Priestley died in America in the year 1804, in the eighty-first year of his age.

While the boundaries of chemistry were so rapidly extending by the discoveries of the British chemists, there were two chemists in Sweden who contributed fully as effectually towards the prodigious revolution which it was so soon destined to undergo: these were Bergman and Scheele.

Torbern Bergman was born in the year 1735, in West Gothland. After finishing his education at the University of Upsala, where he had displayed a decided taste for mathematics and the physical sciences, he was appointed, about the year 1758, magister docens in natural philosophy. In 1767 he succeeded Walerius as professor of chemistry in Upsala, and filled the chair with the highest reputation for seventeen years; for he died on the 8th of July 1784, at the baths of Medevi, to which he had repaired in hopes of an alleviation of his malady. His works were published in six octavo volumes, under the name of Opuscula. It would be tedious to notice all the different facts which Bergman ascertained. It may be sufficient to say, that to him chemistry is indebted for the art of analysis, constituting at present the grand instrument for the improvement of the science. His methods of analysing waters, stony bodies, and ores, were indeed imperfect, but they constituted a beginning which was afterwards improved and new-modelled by Klaproth and Vauquelin, and brought to the state of perfection which it has recently attained by different chemists, who still continue to cultivate the science with ardour.

The other Swedish chemist of that period was Scheele, who constitutes one of the most extraordinary chemists that ever existed. Charles William Scheele was born on the 18th of December 1742, at Stralsund, the capital of Swedish Pomerania. He was bound apprentice to an apothecary in Gottenburg, from which place, after an interval of several years, he went successively to Malmo, Stockholm, and Upsala, and at last he settled at Köping as an apothecary, where he died in 1786, in the forty-fourth year of his age. Scheele’s discoveries were so numerous and important, that a bare catalogue of them will be sufficient to convince the most careless reader of the great services which he performed to the science.

He first pointed out the method of obtaining tartaric add in a state of purity. What a benefit this has been to the manufactures of Great Britain every calico-printer is able to appreciate. He discovered fluoric acid, and pointed out some of its most remarkable properties. He did not, indeed, obtain the acid in a state of purity, but united to silica in the state of fluosilicic acid. Pure fluoric acid was first made known in 1811 by Gay-Lussac and Thénard. His experiments on manganese constitute a memorable era in chemistry. It was during them that he discovered chlorine and barytes, the first of which has quite altered the mode of bleaching formerly followed in this country; and the second is an indispen⅛able article in analysis. It was during these experiments also that he discovered the constituents of ammonia. By heating the bleaching oxide of manganese, he obtained oxygen gas, the remarkable properties of which he ascertained; so that if oxygen had not been discovered by Priestley, it would have been soon after made known by Scheele, who possessed all the merit, though the want of priority deprived him of the reputation which would otherwise have accrued to him.

He discovered arsenic add, molybdic acid, tungstic acid, uric acid, mucic acid, oxalic acid, lactic acid, malic acid, gallic acid, citric acid. He ascertained the constituents of prussic acid, the nature of plumbago, and pointed out the characters of silica and alumina, which till then had been confounded by various chemists of some note. The preceding enumeration contains but an imperfect sketch of the numerous discoveries of Scheele. The necessity of being brief has obliged us to omit much which was highly deserving of notice.

The discoveries of the British and Swedish chemists made known a prodigious number of facts which had not been anticipated by Beecher and Stahl, and which their theory was inadequate to explain. It was clear, therefore, that the Stahlian theory could not much longer maintain its ground. The chemist to w hose exertions that overthrow was immediately owing was Lavoisier.

Antoine Laurent Lavoisier was born in Paris in 1743.; He was opulent, and had received a liberal education, lt was Dr Black’s discovery of fixed air that induced him to make choice of chemistry as a field in which much reputation might be gained. He became a member of the Academy of Sciences in 1768, and from that period till the year 1794, or twenty-six years, he was the author of no fewer than sixty memoirs, most of them upon chemical subjects. In the year 1772 he discovered that when metals are converted into calces, they increase in weight. This led him to suspect the non-existence of phlogiston. This notion he prosecuted with unexampled industry for twenty-four years, till he finally established it to the satisfaction of the chemical world. Combustion, according to his ’ view, is the combination of the burning body with oxygen.< The oxygen loses the gaseous form, and therefore deposits the heat and the light with which it was formerly united. Hence the reason why bodies after combustion are heavier than they were before. Combustible bodies are either simple substances, or combinations of various simple substances. When they undergo combustion, they unite with oxygen. Hence all the products of combustion are compounds. Sulphur, for example, is a simple body. When burnt it combines with oxygen, and is converted into sulphuric acid; so that sulphuric acid is a compound of sulphur and oxygen. In 1786 Berthollet, at a meeting of the academy, declared himself satisfied of the truth of Lavoisier’s opinions. He was soon followed by Fourcroy, who had succeeded Buequet as professor of chemistry in the Jardin du Roi, and was at that time the most popular teacher of the science in France. Soon after Morveau, who had greatly distinguished himself as a chemist, and had given gratuitous lectures on chemistry at Dijon for many years, and who was employed in writing the chemical part of the Encyclopédie Méthodique, was also converted to the same opinions.

The old chemical phraseology was at that time exceedingly imperfect, entirely moulded on the Stahlian theory, and quite inadequate to express the opinions of the anti-phlogistians, as the adherents of Lavoisier were called. Morveau suggested the propriety, or rather the necessity, of forming a new chemical nomenclature; and though his views were at first opposed by the chemical members of the Academy of Sciences, they were finally acceded to; and Lavoisier, Berthollet, Morveau, and Fourcroy, formed themselves into a committee for the purpose of constructing a new chemical nomenclature. The new nomenclature was published in the. year 1787. It was avowedly[7:6:351] the production of Morveau, except a few terms which had been previously introduced by Lavoisier. Though far from perfect, it was so superior to the old barbarous jargon of the science, that it was in a few years almost universally adopted, and contributed more than any thing else to the overthrow of the Stahlian theory; for thinking is so much dependent upon language, and the old nomenclature was so much identified with the Stahlian theory, that, had it continued to be used, it is doubtful whether the hypothesis of phlogiston could have been got rid of, at least so speedily.

Mr Kirwan, who had established a high reputation by his labours as a chemist, undertook the task of refuting the antiphlogistic theory, and with that view published a work, to which he gave the name of An Essay on Phlogiston, and the Composition of Acids. In that book he maintained an opinion which seems to have been pretty generally adopted by the chemists of the time, namely, that phlogiston is the same thing with what is at present called hydrogen, and which, when Kirwan wrote, was called light inflammable air. Of course Mr Kirwan undertook to prove that every combustible substance, and every metal, contains hydrogen as a constituent, and that hydrogen escapes in every case of combustion and calcination. On the other hand, when calces are reduced to the metallic state, hydrogen is absorbed. The book was divided into thirteen sections. In the first, the specific gravity of gases was stated according to the best data then existing; the second section treats of the composition of acids and of water; the third, of sulphuric acid; the fourth, of nitric acid; the fifth, of muriatic acid; the sixth, of aqua regia; the seventh, of phosphoric acid; the eighth, of oxalic acid; the ninth, of the calcination and reduction of metals, and the formation of fixed air; the tenth, of the dissolution of metals; the eleventh, of the precipitation of metals by each other; the twelfth, of the properties of iron and steel; while the thirteenth sums up the whole argument by way of conclusion.

In this work Kirwan admitted the truth of Lavoisier’s theory, that during combustion and calcination oxygen unites with the burning and calcining body. He admitted also that water is a compound of oxygen and hydrogen. Now, these admissions, which, however, it was scarcely possible for a man of candour to refuse, rendered the whole of his arguments in favour of the identity of hydrogen and phlogiston, and of the existence of hydrogen in all combustible bodies, exceedingly inconclusive. Kirwan’s book was laid hold of by the French chemists as affording them an excellent opportunity of showing the superiority of the new opinions over the old. Kirwan’s view of the subject had been taken by Bergman and Scheele, and indeed by every chemist of eminence who still adhered to the phlogistic system. A refutation of it, therefore, would be a death-blow to phlogiston, and would place the antiphlogistic theory upon a basis so secure, that henceforth it would be impossible to shake it. The book accordingly was translated into French, and published with a refutation at the end of every chapter. These refutations were managed with so much urbanity of manner, and at the same time were so complete, that they produced all the effects expected from them. Mr Kirwan, with a degree of candour and liberality, of which, unfortunately, very few examples can be produced, abandoned phlogiston, and adopted the theory of his opponents.

Thus, about the year 1790 or 1792, the doctrinc of Lavoisier may be considered to have been fully established. If any adherents of phlogiston still remained, they were utterly unsuccessful in their feeble attempts to stem the current which had set in with so much violence against them. The science continued to be prosecuted in France and Germany; and, notwithstanding the horrors of the French revolution, and the confusion into which it plunged Europe, Berthollet, Fourcroy, Vauquelin, and Pelletier in France, and Klaproth in Germany, were the individuals to which this progress was chiefly owing. Klaproth in particular extended the bounds of the science by the discovery of several new metals, and by bringing the difficult art of analysis to a regular system. To Vauquelin the science was indebted for the discovery of a new metal and a new earth, and to an infinite number of analyses, mineral, vegetable, and animal, all of them calculated to enlarge our knowledge, and extend the dominion of the science of chemistry.

About the termination of the eighteenth century a new electrical instrument was discovered by Volta, now universally known under the name of the galvanic or Voltaic pile. This new instrument was destined to produce a new revolution in chemistry, nearly as great as the antiphlogistic theory of Lavoisier. About the time that this discovery was made, a new race of chemists had begun to distinguish themselves in Britain. One of the most remarkable of these was Humphry Davy, who was in a great measure self-taught, and who possessed such genius and ardour, that he was sure to make a figure in whatever branch of science he chose to cultivate. His predilection for chemistry was strong, and he saw at once the celebrity likely to accrue from a successful development of the laws which regulate the chemical phenomena connected with the action of the Voltaic battery. He accordingly devoted himself to the study of these phenomena; and about the year 1807 he succeeded in demonstrating that the galvanic energy has the property of decomposing compound bodies according to a determinate law; oxygen and acids attach themselves to the positive pole of the battery, while hydrogen, sulphur, metals,alkalies, and earths, attach themselves to the negative pole. He concluded from this that oxygen and acids are naturally negative, while hydrogen, sulphur, metals, earths, and alkalies are naturally positive. This led to the conclusion that chemical affinity is merely a case of electrical attraction, and that bodies combine because they are in opposite electrical states, and that, in order to produce decomposition, we have only to bring them into the same electrical state. This hypothesis, known by the name of the electrical theory, was generally adopted by chemists; and it is by means of it that the nature of combination and decomposition is at present attempted to be explained.

Davy drew as a consequence from his theory, that if the current of electricity can be made sufficiently large, it will decompose all compound bodies whatever. He tried potash and soda, and succeeded in showing that they are compounds of peculiar metals and oxygen. It was immediately inferred that the earths also are metallic oxides. This was demonstrated by Davy himself with respect to the alkaline earths; and it has been since shown that all the earths proper are also oxides, though the bases of all of them are not metals.

Davy succeeded also (chiefly in consequence of the important labours of Gay-Lussac and Thenard) in satisfying chemists that chlorine is not a compound, but a simple substance, analogous to oxygen in its nature, and, like it, attracted by the positive pole of the Voltaic battery. The subsequent discovery of iodine and bromine, substances analogous in their nature, and the probable evidence that the base of fluoric acid is a substance of a similar kind, have completely new-modelled the Lavoisierian theory. There are five substances analogous to oxigen, which may be called supporters of combustion. They are all capable of uniting with combustible bodies, and the union may be attended with the phenomena of combustion. When they [7:6:352] combine with one set of combustible bodies they form acids; when with another set, alhalies or bases. Thus there are at least five different classes of acids, and as many different classes of alkalies. Acids and alkalies of the same class unite together and form salts; but acids and bases of different classes mutually decompose each other, and in general, therefore, cannot unite. Thus there are as many classes of salts as there are of acids and bases. Such is an imperfect sketch of his present chemical theory, which may be fairly considered as having originated with Sir H. Davy, though it has been carried a greater length than he anticipated, and many new facts have been discovered of which lie was ignorant.

Another improvement has been introduced into chemistry by Mr Dalton, which is, if possible, still more important, by affording a test of accuracy in our experiments, and enabling us to eliminate errors by a method somewhat analogous to that. employed by astronomers. Even at present, while only in its infancy, this improvement has made a complete alteration in the mode of experimenting. What may not be expected from it when it has come to a state of maturity? The improvement to which we allude is usually known by the name of the atomic theory.

This theory did not originate at once, but was gradually brought into light. A short account of the steps by which it came into view will terminate this imperfect historical detail of the progress of chemistry. The very attempt at analysis is an acknowledgment that bodies unite only in definite proportions; for unless this were the case, all attempts to determine the proportions in which the constituents of bodies are united, would be obviously absurd. The first accurate set of experiments to analyse the salts was made by Wentzel, and published by him in 1777, in a small volume entitled Lehre von der Verwandschaft der Körper, or Theory of the Affinities of Bodies. These analyses are much more accurate than those of Bergman, yet the book fell almost dead-born from the press. Wentzel was struck with a phenomenon, which had indeed been noticed by preceding chemists; but they had not drawn the advantages from it which it was capable of affording. There are several saline solutions, which, when mixed with each other, completely decompose each other, so that two new salts are produced. Thus, if we mix together solutions of nitrate of lead and sulphate of soda, in the requisite proportions, the sulphuric acid of the latter salt will combine with the oxide of lead of the former, and will form with it sulphate of lead, which will precipitate to the bottom in the state of an insoluble powder, while the nitric acid formerly united to the oxide of lead will combine with the soda formerly in union with the sulphuric acid, and form nitrate of soda, which being soluble, will remain in solution in the liquid. Thus, instead of the two old salts, sulphate of soda and nitrate of lead, we obtain the two new salts, sulphate of lead and nitrate of soda. If we mix the salts in the requisite proportions the decomposition will be complete; but if there be an excess of one of the salts, that excess will still remain in solution without affecting the result. If we suppose the two salts anhydrous, then the proportions necessary to complete the decomposition are,
[table]

We see that the absolute weights of the two sets of salt are the same. All that has happened is, that both the acids and both the bases have exchanged situations. Now, if, instead of mixing them in the above proportions, we employ sulphate of soda 9, and nitrate of lead 25∙75∙, that is to say, if we employ five parts of nitrate of lead more than is sufficient for the purpose, we shall have exactly the same decomposition as before. But the five of excess of nitrate of lead will rema'ņ in solution mixed with the nitrate of soda. These will be precipitated as before—sulphate of lead 19; and there will remain in solution nitrate of soda 10∙75, and nitrate of lead 5. The phenomena are precisely the same as before. The additional five of nitrate of lead has occasioned no alteration. The decomposition has gone on just as if they had not been present.

Now, the phenomenon which drew the particular attention of Wentzel is, that if the salts were neutral before being mixed, the neutrality was not affected by the decomposition which took place on their mixture. A saltis said to be neutral when it neither possesses the character of an acid nor an alkali. Acids redden vegetable blues, while alkalies render them green. A neutral salt possesses no effect whatever on vegetable blues. This observation of Wentzel is very important. It is obvious that the salts, after their decomposition, could not have remained neutral, unless the elements of the two salts had been such that the bases in each just saturated the acids in either of the salts. The constituents of the two salts are as follows:—
[table]

It is obvious from this that five sulphuric acid just saturate four soda and fourteen oxide of lead; while 6∙75 nitric just saturate the same quantities of each of these bases. Thus the saturating powers of soda and oxide of lead are to each other as 4 to 14; while the saturating powers of sulphuric and nitric acids are to each other as 5 to 6 ’ 75.

In the year 1792 another labourer in the same department of chemistry appeared. This was Jeremiah Benjamin Richter, a Prussian chemist, who died in the prime of life in the year 1807. In 1792 lie published a work entitled Anfangsgründe der Stochiometrie ; oder Messkunsi Chymischer Elemente, Elements of Stochiometry, or the Mathematics of the Chemical Elements. ∙ A second and third volume of this work appeared in 1793, and a fourth in 1794. The object of the book was a rigid analysis of the different salts, founded on the fact just mentioned, that when two salts decompose each other, the salts newly formed are neutral as well as those which have been decomposed. He took up the subject nearly in the same way as Wentzel had done, but advanced much farther, and endeavoured to determine the capacity of saturation of each acid and base, and to attach numbers to each, indicating the weights which mutually saturate each other. He gave the whole subject a mathematical dress, and endeavoured to show that the same relation existed between the numbers representing the capacity of saturation of these bodies, as does between certain classes of figurative numbers. When we strip the subject of the mystical form under which he presented it, the labours of Richter may be exhibited under the two following tables, [7:6:353] which represent the capacity of saturation of the acids and bases, according to his experiments.
[table]

To understand this table it is only necessary to observe, that if we take the quantity of any of the acids placed after it on the table, that quantity will, according to Richter, be exactly saturated by the weight of each base put after it in the second column. Thus 1000 grains of sulphuric acid will be saturated by 525 grains of alumina, 615 of magnesia, 672 of ammonia, 793 of lime, and so on. On the other hand, the quantity of any base placed after its name in the second column will be just saturated by the weight of each acid placed after its name in the first column. Thus 793 parts of lime will be just saturated by 427 parts of fluoric acid, 577 of carbonic acid, 706 of sebacie acid, and so on.

Richter’s labours in this important field produced as little attention as those of Wentzel. Indeed, as his experiments were far from accurate, and his numbers not exact, the accuracy of his principles was not at first sight perceptible. However, his views were not altogether overlooked. They were appreciated by Berzelius, who devoted several years to put them to the test of experiment, and who was at last able, by gradually bringing the analysis of the salts nearer and nearer to perfection, to see the justice of the principle which Richter had spent his life in endeavouring to establish.

Mr Dalton of Manchester had laid the foundation of the high reputation which he has so justly obtained by his papers on Vapour, published in the Memoirs of the Literary Society of Manchester in the year 1802. Soon after this, probably as early as 1803, he began to speculate respecting the nature of the ultimate elements of bodies. He had been occupied in determining the composition of the two gases distinguished by the names of carburetted hydrogen and olefiant gas. He observed, that for complete combustion they require different but determinate quantities of oxygen gas. A volume of carburetted hydrogen requires for complete combustion two volumes, while a volume of olefiant gas requires three volumes of oxygen gas. When one volume of carburetted hydrogen is burnt, there is formed just one volume of carbonic acid gas; but when a volume of olefiant gas is burnt, there are formed two volumes of carbonic acid gas, or double the former quantity. Now, carbonic acid is a compound of oxygen and carbon. The oxygen gas supplies the first of these, and the inflammable gases the second. It is clear from the experiment, that the quantity of carbon in a voluμιe of olefiant gas is just twice as great as that in a volmńe of'carburetted hydrogen. It had been shown by Lavoisier that carbonic acid’gas contains just its own bulk of oxygen ġäs. It is evident from this that one of the two volumes of oxygen gas employed in the combustion of carburettćd hydrbgěn went tb the formation of carbonic acid; wliilé tŵb of the three volumes employed in the combustion of'olefiant gas went to’ the same purpose.

There remained in each combustion one volume of oxygen gas, which was employed in uniting to hydrogen contained in each gas, and in forming water. Now, as the quantity of oxygen necessary to convert the hydrogen into water is the same in each, it is clear that a volume of each gas contains exactly the same quantity of hydrogen. In this way did Mr Dalton, with much sagacity, demonstrate that a volume of carburetted hydrogen gas and of olefiant gas contains each the same weight of hydrogen; but that the weight of carbon in the latter gas is just double that in the former.

This led him to attend to the nature of the ultimate particles of bodies; and he concluded, with the ancients, that they consisted of atoms incapable of further diminution or division. It was known already, that when bodies unite chemically, it is the ultimate particles or atoms that unite. And he concluded (very naturally), from the facts above stated respecting the combustion of the two inflammable gases, that carburetted hydrogen is a compound of one atom hydrogen and one atom carbon; while olefiant gas is a compound of one atom hydrogen and two atoms carbon. He inferred further, that every atom of a body (viewed along with its atmosphere of heat) is a sphere. He represented an atom of hydrogen by the symbol Θ (a circle with a dot in the centre), and an atom of carbon by the symbol @ (a circle blackened in the inside); and he denoted an integrant particle of the two gases in the following manner :—
[table]

The former is a binary compound, or a compound of two atoms; while the second is a ternary compound, or a compound of three atoms.

It was this happy idea of representing the atoms of bodies by symbols that gave Mr Dalton’s opinions so much clearness. Oxygen was represented by O (a circle); azote by φ (a circle with a vertical diameter). The composition of several of the best-known bodies was represented by him as follows :—
[table]

It is easy to see (if this view be correct), that if we can determine the composition of these bodies with accuracy, we shall have the ratios of the weights of the atoms of the simple bodies. For example, Dalton concluded from his experiments, that carburetted hydrogen is composed of
[table]

Now, as the former gas is a compound of one atom of hydrogen and one atom of carbon, it follows that the weights of the atoms of hydrogen and carbon are to each other as the numbers one to five. If, therefore, we represent the weight of the atom of hydrogen by one, that of carbon will be five.
[table]

then (if its symbol be Ο Θ) it is clear, that if the atom of hydrogen be unity, that of oxygen will be eight. In this way the weight (or at least the ratios of the weight) of the atoms of all the simple bodies may be determined by an accurate analysis of the compound bodies formed by the union of these simple bodies.
[7:6:354]

When Mr Dallon first started the atomic theory, it was not possible to determine the weights with any thing like an approach to accuracy, because at that time chemistry did not possess a single analysis which could be considered as even approaching to accuracy. We need not be surprised then that Mr Dalton’s first numbers were not exact. It required infinite sagacity, and not a little labour, to come so near the truth as he did. In consequence of this state of the science, neither the importance nor the truths of the theory were at first appreciated; and several chemists, from whom better things might have been expected, refused to admit it, and even turned the whole doctrine into ridicule. It may be sufficient to mention Sir Humphry Davy, who expressed himself very strongly at first in opposition to the atomic theory.

The first direct proofs in favour of the theory were advanced by Dr Wollaston, who showed the existence of three salts composed of oxalic acid and potash, the oxalate, binoxalate, and quateroxalate. In these, if the quantity of potash be reekoned unity, that of oxalic acid will be respectively one, two, and four. Hence he concluded, that oxalate of potash is a compound of 1 atom potash + 1 atom oxalic acid; binoxalate, of 1 atom potash + 2 atoms oxalic acid; and quateroxalate, of 1 atom potash + 4 atoms oxalic acid. He showed also that carbonic acid and potash unite in two proportions, forming carbonate and bicarbonate of potash; the former composed of 1 atom potash + 1 atom carbonic acid, and the latter of 1 atom potash + 2 atoms carbonic acid. About the same time Dr Thomson showed that* there are two oxalates of strontian, the oxalate and binoxalate, the former composed of 1 atom strontian + 1 atom oxalic acid, and the second of 1 atom strontian and 2 atoms of oxalic acid. Some years after, M. Berzelius brought forward a great many examples, and fully confirmed the great principle of Richter. It was easy to apply this principle to the atomic theory of Dalton, and to show that it was merely a case of this theory. In consequence of these confirmations the atomic theory gradually gained ground, and was at last universally adopted by chemists. But it was adopted with two different modifications.

In the year 1809 M. Gay-Lussac published, in the second volume of the Mémoires dArcueil, a paper on the union of the gaseous bodies with each other. In this paper he shows that the proportions in which the gases unite with each other are of the simplest kind, one volume of one gas either combining with one volume of another, or with two volumes, or with half a volume. The atomic theory of Dalton had been opposed with considerable keenness by Berthollet, in an introduction which lie prefixed to the French translation of Dr Thomson’s system of chemistry. Nor was this opposition to be wondered at, because it was evident that its admission would overturn the opinions which Berthollet had laboured to establish in his Chemicμl Statics. The object of Gay-Lussac’s paper was to confirm and establish the atomic theory, by exhibiting it in a new point of view. Nothing can be more ingenious than his mode of treating the subject, or more complete than the proofs which lie brings forward in support of it. It had been already established that water is formed by the union of one volume of oxygen with two volumes of hydrogen gas. Gay-Lussac found by experiment that one volume of muriatic acid gas is just saturated by one volume of ammoniacal gas. Fluoboric acid unites in two proportions with ammoniacal gas; one volume of the acid gas with one and with two volumes of the alkaline gas. Carbonic acid gas and ammoniacal gas unite also in two similar proportions. M. A. Berthollet had proved that ammonia is a compound of one volume of azotic and three volumes of hydrogen gas; and Gay-Lussac had shown that sulphuric acid is a compound of one volume of sulphurous acid gas and half a volume of oxygen gas. He showed further, that the compounds of azote and oxygen are composed as follows:
[table]

He showed also, that when two gases, after combining, remain in the gaseous state, the diminution of volume is either 0, or ļ, or

The constancy of these proportions left no doubt that the combinations of all gaseous bodies were definite. The theory of Dalton applies to them with great facility. We have only to consider a volume of gas to represent an atom, and then we see that in gases one atom of one gas combines either with one, two, or three atoms of another gas, and never, or very seldom, with more.

In this country chemists have in general adopted the simple theory of Dalton. But Berzelius has founded his notions of the atomic theory upon the doctrine of volumes of Gay-Lussac; and this view of the subject has been generally embraced on the Continent. The principal difference between the two views consists in the composition of water. Whenever hydrogen and oxygen gas are burnt, in what proportion soever they are mixed, they form water; and they cannot be made to unite directly in any other proportion. This induced Dalton to consider water as a compound of one atom oxygen and one atom hydrogen. But water being composed by weight of eight parts of oxygen and one part of hydrogen, it follows from this, that the atom of oxygen is eight times heavier than the atom of hydrogen. On the other hand, water is formed by the union of two volumes of hydrogen with one volume of oxygen gas. Hence, if we consider a volume of a gas as in all cases equivalent to an atom, it will follow that water is a compound of two atoms of hydrogen and one atom of oxygen. This would make an atom of oxygen sixteen times heavier than an atom of hydrogen. Thus, we have two different atomic weights for hydrogen, one adopted in Great Britain, and another on the Continent. Nor has it yet been decided by decisive arguments which of these two views is correct. Analogy is in favour of the view taken by British chemists; but further investigations ' will be necessary, and more knowledge of the subject must be obtained, before a final decision can be made.

Though chemists have agreed to consider all those bodies which they have been unable to decompose as simple, yet by that term they do not mean to insinuate that they are absolutely simple, but merely that, relative to our state of knowledge, they cannot be reduced into simpler constituents. It is by no means impossible that the metals themselves may be compounds. But as no one has hitherto succeeded in decomposing them, or has been able to produce any plausible evidence of their being compounds, we are obliged to consider them as simple. Succeeding chemists may in progress of time be more fortunate than we are, and may be able to show that they are all compounds. When this happens, a new set of simple bodies will come into view, of which at present we have no notion.

To the ultimate integrant part of those bodies which we consider as simple, we apply the term atoms ; and the weights (or rather the ratios of the weights) of these atoms have been determined in numbers. Thus an atom of copper weighs 4, an atom of iron 3∙5, and an atom of lead 13. Should it be discovered hereafter that these metals are compounds of two ingredients, it is clear that the atomic weight of these two ingredients must be such that their [7:6:355] sum will be equal to the present atomic weight of the metal. Thus, for example, the atomic weight of potash is 6. For a long period potash was considered as a simple body, till Davy ascertained that it is a compound of potassium and oxygen. The atom of potassium weighs 5, and that of oxygen is 1. Now 5 + 1 = 6, the atomic weight of potash.

These observations are sufficient to show the probability that all our atoms are compounds. Hence it is conceivable that they may admit of subdivision. This makes the existence of half atoms and thirds of atoms, which we are obliged to admit occasionally, cease to be an absurdity. Indeed, from some facts that have of late come into view, it is not unlikely that the atoms of simple substances may usually appear united in groups of two, three, or more atoms. Hence what we call an atom may probably be a congeries of two or more atoms. Should this be the case, the existence of half or a third of an atom would no longer be problematical. We shall find that oxygen, water, and even hydrogen, not unfrequently combine to the amount of half an atom or the third of an atom.

Having thus finished our historical sketch of the progress of chemistry, it is now time to enter upon a detail of the great collection of facts which constitute the body of the science. For the sake of perspicuity we shall divide the subject into four parts. In the first part we shall treat of the laws of combination and decomposition ; in the second, of the chemistry of inorganic bodies ; in the third, of the chemistry of vegetable bodies ; and in the fourth, of the chemistry of animal bodies. Of these four parts, the second, in the present state of the science, is most important, and must therefore be treated most in detail.
PART I.

OF THE LAWS OF CHEMICAL COMBINATION AND DECOMPOSITION.

1. When bodies uñite chemically, it is the atoms or ultimate particles of each which combine; not large masses of matter. Thus, when copper combines with oxygen, it is converted into a black powder called oxide of copper. How small soever the quantity of this black powder which we examine, we shall find in it both copper and oxygen. This oxide is formed by the union of an atom of copper with an atom of oxygen.

2. Now the atoms of bodies are small to a degree of which we can form no adequate conception. Gold leaf is beat out so thin, that 50∙7 square inches of it weight only one grain. Now the 1000th part of a line or inch is easily visible through a common pocket-glass. A square inch of gold therefore is divisible into a million of parts, each visible through a common microscope. Hence it follows, that when gold is reduced to the thinness of gold leaf, yōTüo'īľōōth °f a g ra i∏ of gold may be distinguished by the eye. But Reaumur has shown that one grain of gold of the thinness which it is upon silver wire, will cover an area of 1400 square inches. It is plain that in this case rrōüōľmTōō^ 1 °f a grain of gold may be rendered visible. But small as this particle is, we have no reason for believing that it does not constitute a considerable number of atoms.

3. But small as these atoms are, the ratios of their weight to each other have been determined with considerable exactness. The weight of the atom, together with the specific gravity of a body, enables us to determine its relative volume. In this way may the volumes of the atoms of different bodies be determined. The following table exhibits these bulks, that of carbon being reckoned one.
[table]

4. We have no means of determining the shape of these atoms, but the most commonly received opinion is that they are spherical, or at least spheroidal.

5. When the atoms of two different bodies unite, the compound which they form differs so much in its properties from the constituents, that we could form no notion whatever what these constituents are. Thus, water bears no resemblance whatever to either of its constituents, oxygen or hydrogen ; nor saltpetre to its constituents, nitric acid and potash.

6. When bodies combine chemically, the union is always accompanied by a change of temperature. Sometimes the temperature sinks, but in by far the greater number of cases it rises.

7. When two substances unite chemically, the bulk of the compound is very seldom exactly the same as that of its constituents. In most cases the bulk diminishes, in a few cases it increases, and in some rare instances no alteration in bulk whatever takes place. One volume of azotic, and half a volume of oxygen gas united, constitute only one volume of protoxide of azote. When copper and gold are melted together, the bulk of the compound is greater than that of the two constituents before their union; 916⅛ cubic inches of gold and 83j∙ of copper, after union, become 1029 cubic inches, instead of 1000, which was their bulk before combination. Finally, one volume of azotic and one volume of oxygen gas united, constitute two volumes of deutoxide of azote; so that no alteration of bulk whatever has taken place.

8. When bodies are chemically united with each other, we cannot separate them again by filtration, or any mechanical means whatever. Heat sometimes enables us to produce a separation, but in the greater number of cases this expedient is quite unsuccessful. When a volatile substance is united to another which is more fixed, it cannot be again separated so easily by applying heat as we might be led to expect from our knowledge of the difference between the volatility of the two constituents. Sulphuric acid does not boil till heated above 600°, while water boils at 212°. But a mixture of sulphuric acid and water does not boil till much hotter than 212°; and what is driven off by boiling is not water, but a compound of sulphuric acid and water.

9. It is therefore impossible, in the greater number of cases, to separate substances that have been combined,, either by mechanical means or by the application of heat.' But by multiplying experiments in the way of mixture, a, discovery has been made which has been of infinite use to-chemists, and has greatly enlarged their power over compounds[7:6:356]. It has been found that the addition of some third body to a compound of two ingredients which are strongly united by chemical combination, will in many cases dispose them to separate from each other. The third body unites to one of the constituents of the compound, and sets the other constituent at liberty. Thus, if we add potash in the requisite quantity to a compound of sulphuric acid and water, it will combine with the acid, and set the water at liberty. If we now apply heat, the water may be distilled off pure, while sulphate of potash remains behind. The whole art of chemistry consists in forming compounds by uniting different bodies with each other; and he is the best and most skilful chemist who knows what third body will answer to effect the decomposition which he has in view.

10. The phenomena of combination and decomposition were at first explained by chemists by the application of supposed mechanical powers. When a fluid has the property of dissolving a solid body, it was supposed to abound in sharp and pointed particles, having the form of needles or wedges, which were agitated in the fluid with a rapid and confused intestine motion. The solid again was supposed to contain pores of such sizes and shapes as were fitted to the pointed particles of the fluid. These pores were penetrated by the fluid, and the solid torn asunder. The precipitating bodies again were supposed to be porous and spongy; and by this configuration, and by a confused motion, they break the spiculae of the solvent, and thus allow the solid again to fall down. This explanation is so crude and unsatisfactory, that it is not entitled to the honour of a refutation.

11. The first attempt at a rational explanation of chemical combination was by Sir Isaac Newton. He had demonstrated that the planets are retained in their orbits by the attraction of gravitation. He conceived that there are other forces or principles of motion in nature, by which certain bodies act, or appear to act, at sensible distances from each other. This is the case with the attractions and repulsions connected with electricity and magnetism. He suspected that there are still other forces whose sphere of action is confined to the ultimate particles or atoms of bodies. Capillary attraction, and the inflection and deflection of light, are examples of such actions. Chemical combinations and decompositions, in his opinion, depend upon powers somewhat resembling the others. He was of opinion that the ultimate particles of certain bodies attract each other with a certain unknown but enormous force, v which begins to exert itself only at very minute distances. Hence, when such bodies are mixed, the particles of each being brought within the requisite distance, this force exerts itself, and the bodies unite. The decomposition produced by a third body he ascribes to the superiority of the attraction of this third body for one of the constituents of the compound, in consequence of which it unites with that constituent, and separates the other which was previously in combination.

These views of Newton made their way into the science very slowly; but before the middle of the eighteenth century they seem to have been almost universally adopted. Chemists, however, instead of the term attraction employed by Newton, substituted affinity, first introduced into chemistry by Dr Hook, and caught with avidity by the chemists on the Continent. By chemical affinity then is meant that unknown force which causes the ultimate particles of different bodies to unite together, and to remain united.

As soon as the Newtonian notions of affinity were adopted by chemists, they naturally concluded, that when a compound a b was decomposed by the body c, which combined with b, disengaging a, this was because c had a stronger affinity for b than a had. Decomposition therefore came to be considered as the measure of the strength of affinity. In the year 1718, M. Geoffroy, senior, thought of arranging bodies in the order in which they separate each other from a given substance. Bodies thus arranged were considered as exhibiting the order of the affinity of the respective bodies for the substance with which they united; that body being placed highest which had the strongest affinity, or was capable of displacing all the others. The rest of the bodies were placed in the.order of their affinity. The following little table will show the nature of Geoffroy’s method.

Sulphuric Acid.

Barytes. Soda.

Strontian. Lime. Potash.

Magnesia.

All the substances in the table combine, or have an affinity, for sulphuric acid. If magnesia, which is at the bottom of the table, be united to sulphuric acid, the addition of lime, soda, potash, or any of the substances in the table, will separate it. Lime will be separated by any of the substances except magnesia; potash will be separated by barytes or strontian, but not by soda, lime, or magnesia. Barytes, which stands highest, will be separated by none, while it separates all below it. In short, every substance in the table is capable of separating sulphuric acid from all the bodies placed below it, but not from those placed above it.

The tables of Geoffroy were necessarily very imperfect, but they were successively improved by Gellert, Lim∙∙ bourg, &c.; and in 1775 a very copious table of elective attractions, as he termed affinity, was published by Bergman. This work of Bergman appears to have fixed the opinions of chemists in general to his own views of the subject. According to him, the affinity of each of the bodies a, b, c, d, &c. for x differs in intensity in such a manner that the intensity of the affinity of each may be expressed by numbers. He was of opinion also that affinity is elective, in consequence of which, if a have a greater affinity for x than b has, if we present a to the compound bx, x separates altogether from b, and unites to ű.

These opinions of Bergman continued to be admitted till Berthollet published his Clιemical Statics in 1803. He considered affinity as an attraction similar to that which exists between the planetary bodies. But in consequence of the very small distance between the attracting bodies, the strength of affinity depends not merely upon the quantity of matter which they contain, but likewise upon their shape. Affinity being an attraction, must always produce combination; and its strength must increase with the mass of the attracting body. According to this doctrine of Berthollet, affinity is not elective. A substance which has a stronger affinity is not capable of separating those which have a weaker affinity; or, if this happens, some other cause intervenes. It will be acknowledged that Berthollet was successful in overturning Bergman’s notions of elective attraction ; for Bergman’s explanation, why a body having a stronger affinity is capable of displacing one having a weaker affinity, is not satisfactory.

But Berthollet’s own views were not more solid than those of Bcrgman. He denied that bodies united in definite proportions’, but affirmed that they were capable of combining in all proportions whatever. This occasioned a controversy between him and Proust, in which the latter was obviously victorious.

The electrical theory, first started by Sir H. Davy, has [7:6:357] enabled us at last to form some idea of the way in which one substance is capable of displacing another. Oxygen, chlorine, bromine, and iodine, are always in a negative state; while the other simple bodies are positive. Hence the reason why these four bodies have a tendency to combine with all the others. Potassium is strongly positive, while oxygen is strongly negative. Hence the strong affinity which exists between these two bodies, and the difficulty of decomposing them when united. If a current of chlorine gas be passed through hot potash (which is a compound of potassium and oxygen), the oxygen is disengaged in the state of gas, and the chlorine unites to the potassium in its place. This decomposition is brought about by the agency of two forces. Chlorine, like oxygen, is negative. It is therefore attracted by potassium and repelled by oxygen. The heat acts partly perhaps by diminishing the cohesion that exists between the particles of potash, but chiefly by exalting the negative energy of the chlorine. This energy, when increased by heat, is greater than that of oxygen. Hence its attraction for potassium must exceed that of.oxygen for the same base. It therefore takes the place of the oxygen; and the mutual repulsion between chlorine and oxygen, together with the elasticity of the oxygen, is sufficient to cause that principle to fly off and make its escape.

The reason why many bodies require a red heat before they combine, and why, when raised to that temperature, they unite with great energy, may be conceived from the data furnished by the electric theory of affinity. Let us take the case of oxygen and hydrogen gases.' The former of these bodies is negative, and the latter positive. They have therefore a strong attraction; but this attraction is not sufficient to overcome the mutual elasticity of the two gases, occasioned probably by an atmosphere of heat surrounding the atoms of each. But a red heat exalts the electric energies of both so much that they are enabled to overcome the resistance occasioned by the elasticity of the gases, and in consequence to combine together.

To what circumstance the negative state of oxygen, chlorine, bromine, and iodine, and the positive state of the other simple bodies, is owing, cannot be explained. Were we to admit, with electricians in general, that negative and positive electricity constitute two distinct fluids, it would follow that a coating of negative electricity must be deposited on the surface of the particles of the simple supporters, while a coating of positive electricity is deposited on the surface of the other simple bodies. These electricities arc attached to the respective bodies in a way which we cannot at present explain; but from the well-known phenomena of electricity, it can scarcely be doubted that the electricities are not inseparably attached, but capable of being increased or diminished according to the laws which bodies follow with regard to electricity. Hence it happens that a substance may be in one electrical state when compared with one body, and in another electrical state when compared with another. In oxygen there is a great preponderancy of negative electricity; it is negative with respect to every other body. Sulphur is negative with regard to most bodies, but it is obviously not so powerfully negative as oxygen. Let us suppose an atom of sulphur to be placed within a very small distance of an atom of oxygen. We know that the two electricities will act on each other. The negative electricity of the oxygen atom will repel the negative electricity of the sulphur; and as an atom of oxygen is almost twice the size of an atom of sulphur, and contains a much greater quantity of negative electricity, it is evident that it will act with greater energy. A portion of the negative electricity of the sulphur will be driven off, while the positive electricity will accumulate in it, in consequence of the attraction exercised on it by the negative* electricity of the oxygen. Positive electricity will accumulate in the sulphur, and negative electricity will diminish. This will of course render it positive, though, before the action of the oxygen on it, it had been negative. In consequence of these two different states, the two atoms combine, and the attraction subsisting between the two electricities will prevent any alteration in their state as long as they remain united. Thus we may conceive how an atom may be positive when it combines with one body, and negative when it combines with another. Hence the reason why oxygen is capable of combining with the other supporters, and why the different positive bodies are capable of uniting with each other. Thus sulphur and phosphorus unite with the metals, and the different metals with each other.

Salts are composed of an acid united to an alkali, usually atom to atom; and it is generally observed that they∣ are more difficult of decomposition than the acids and 1 bases of which they are constituted when in an insulated state. Thus sulphuric acid is decomposable at a red heat; but sulphate of potash may be exposed to a red heat without undergoing any alteration. The reason of this increase of permanence is probably owing to the way in which the constituents combine. The acid being composed of two constituents, one of which is positive and the other negative, may be represented thus, -∣ . The alkaline base being similarly composed, may be represented by the same symbol, 1-. Now there can be little doubt that the acid and base, when combined, will arrange themselves thus,

+ - l·

That is to say, the positive ingredient of the one will attach itself to the negative ingredient of the other. Thus every negative body will be placed between two positive, and every positive between two negative—a situation which ought to increase the firmness and steadiness of the compound.

The black or gray oxide of manganese employed for ob- taining oxygen and chlorine, is a compound of one atom? of manganese and two atoms of oxygen. When strong? sulphuric acid is poured over this compound, one half of j the oxygen of the oxide is disengaged, and makes its escape in the gaseous form, while the sulphuric acid unites with protoxide of manganese, and forms a sulphate of manganese. To account for this curious decomposition, it may be observed, in the first place, that manganese is the most positive of all the metals. Hence it is capable of uniting with and condensing into a solid no fewer than three atoms of oxygen, although the size of an atom of oxygen is more than four times as great as that of an atom of manganese. When manganese is united with only one atom of oxygen, it still retains its positive nature so strongly as to possess powerful alkaline qualities, and to be capable of uniting with and neutralizing the different acids. But when it has combined with three atoms of oxygen, it has become negative, and possesses the characters of an acid. Hence three atoms of oxygen are more than capable of neutralizing an atom of manganese. Even the gray oxide (containing two atoms of oxygen united to one atom of manganese), though nearly neutral, rather leans to an acid than a base, as it is capable of uniting indefinite proportions with barytes and lime. But the second atom of oxygen cannot be retained by the manganese with the same force as the first atom.

Sulphuric acid is a compound of one atom of sulphur and three atoms of oxygen. The oxygen is obviously not neutralized by the sulphur, for the compound possesses strong acid properties. Here then we have two bodies brought into contact, containing both oxygen in considerable[7:6:358] quantity, and not neutralized by the bases with which it is combined. The oxygen in both being highly negative, it is obvious that the atoms of it must repel each other. The volume of the sulphur atom, being much larger than that of the atom of manganese, acts with most energy in retaining the oxygen. The protoxide of manganese being positive, will be attracted by the sulphuric acid, while the second atom of oxygen united to the manganese will be repelled by the oxygen in the acid, and even by the other atom of oxygen united to the manganese. It will therefore be expelled, and sulphate of manganese formed.

It may be asked why the same decomposition of gray oxide of manganese does not take place when nitric acid is poured over it. The reason seems to be, that the azote, the atom of which is of the same size with that of oxygen, more completely neutralizes the oxygen in the nitric acid. It does not therefore act with so much energy in repelling the oxygen united to the manganese; but that it acts is evident, because when a little sugar is added to the mixture, the second atom of oxygen in the oxide combines with carbon, and the nitric acid immediately forms a nitrate of manganese.

Chlorine decomposes lime, or oxidc of calcium as it may be called, because, when assisted by heat, it becomes more negative than oxygen: it therefore repels the oxygen, and attracts the calcium; and these two forces acting together arc sufficiently strong to expel the oxygen from the calcium, and enable the chlorine to take its place. When a body is applied to a binary compound which is capable of combining with both its constituents, it seldom fails to produce decomposition, though it would not have been able to have effected it had it been capable of uniting only with one of the constituents. For example, when charcoal heated to redness is placed in contact with steam, it decomposes that fluid, though hydrogen, being more strongly positive than carbon, ought not to be disengaged from oxygen by that substance. The reason of the disengagement is, that the charcoal combines both with the oxygen and the hydrogen of the water, to the one being positive, and to the other negative. It is for the same reason that oxygen is capable of decomposing many sulphurets, while sulphur equally decomposes many oxides.

When two neutral saline solutions are mixed, we would naturally expect that the two salts should unite together and form a double salt. This frequently happens. But often also they show no tendency to unite; and when the mixed saline solution is evaporated, the two salts crystallize separately.

The tables which originated with Geoffroy, and which Bergman improved so much, instead of being called tables of affinity, should be considered as merely representing the order of decomposition. And if the order of decomposition were regular and unvaried, such tables would be of considerable utility. The order of decomposition seems to be intimately connected with the electric state of the respective bodies. The reason why it varies seems to be, that the electrical state of a body is susceptible of variation according to the temperature, being exalted by heat and depressed by cold. The following table exhibits the non-metallic bodies in the order of their electricity, beginning with the most positive, and ending with the most negative :
[table]

Hydrogen is positive with respect to every body, and oxygen is negative with respect to every body. Sulphuris positive with regard to all the substances below it in the table, but negative with regard toall the substances above it.

The following table exhibits the substances with which each of these bodies is capable of combining, arranged according to their greatest electro-negative energy,and therefore in the order in which they decompose each other:—
[table]

As we know of no substance more electro-negative than oxygen, of course no column under oxygen can be drawn up. These columns are, several of them, necessarily imperfect, from the combinations of the substances standing at the head of them being still imperfectly known; but so far as they go, they mark the order of decomposition. The order of separation is the position in which they stand in the column, every substance being capable of separating all the bodies below it from the substance standing at the head of the column, but none of the substances placed above it. The bromine is capable of separating iodine, sulphur, selenium, &c. from hydrogen, but not oxygen, fluorine, or chlorine.
PART II.

OF THE CHEMISTRY OF INORGANIC BODIES.

We shall arrange the facts belonging to this part of our subject, which are the most copious and important of all, into three divisions. In the first we shall treat of simple, substances, in the second of primary compounds, and in the third of secondary compounds. division I.—OF SIMPLE SUBSTANCES.

The simple substances at present known amount to fifty-four in number. Of these there are five which seem capable of combining with all the others. They are the [7:6:359] most electro-negative of all known bodies. Hence, when compounds containing them are decomposed by galvanism, they always attach themselves to the positive pole. When they combine with a certain portion of the other simple bodies, they form with them acids ; when with the rest, they constitute bases or alkaline bodies, capable of uniting with and neutralizing the acids. To these five bodies the name of supporters of combustion may be given. The eighteen bodies which, when combined with the supporters, become acids, may be distinguished by the name of acidifiable bases. The thirty-one bodies which, when united with the supporters, become alkalies, may be called alkalifiable bases. These three sets of simple bodies will occupy our attention in the three following chapters.

CHAP. I.—OF THE SIMPLE SUPPORTERS OF COMBUSTION.

The simple supporters of combustion at present known are the following five:
[table]

They act so important a part in chemistry, that the student requires to be made acquainted with them as early as possible. We shall treat of them successively in the five following sections.

Sect. I.— Of Oxygen.

Oxygen is a gaseous or aerial substance, and constitutes a portion of the atmosphere. It was discovered by Dr Priestley on the 1st of August 1774, and called by him deplilogisticated air ; Scheele discovered it before 1775, and called ∖ tempyreal air; Condorcet gave it the name of vital air; and Lavoisier (from a plausible but erroneous hypothesis) contrived the term oxygen, by which it is now generally known. By oxygen he meant the generator or producer of adds.

It may be obtained by exposing black oxide of manganese in fine powder to a red heat in an iron bottle, to which a metallic tube with a joint is fixed air-tight, in order to convey it to the proper gas-holders, which may be either copper vessels or glass jars filled with water, standing inverted on the shelf of the pneumatic trough. It may be obtained also by mixing strong sulphuric acid with black oxide of manganese in a glass retort, and applying the heat of a lamp to the mixture. The purest oxygen gas of all is obtained by putting about an ounce of chlorate of j)otash into a very small green glass retort with a long beak, and heating it to redness over a charcoal fire. The salt melts, and yields pure oxygen gas in great abundance.

i. Oxygen gas is colourless, destitute of taste and smell, and possessed of all the mechanical properties of atmospherical air. Its specific gravity is 1∙1111, that of common air being reckoned unity. Hence, at the temperature of sixty degrees, and when the barometer stands at thirty inches, a hundred cubic inches of oxygen gas weigh 34∙60 grains.

Combustible bodies burn in it with more splendour, and give out more heat and light, than when they burn in common air. Animals breathe it without inconvenience for a much longer time than they can do the same bulk of common air.

It has been demonstrated that common air, not reckoning some vapour of water and some carbonic acid which it always contains, is a mixture of oxygen gas and azotic gas in the proportion of 20 volumes of the former and 80 of the latter.

Oxygen refracts light rather badly. If the refracting power of air be unity, that of oxygen gas, according to Dulong, is 0∙324. * - λ ---

Oxygen has the property of combining with every other simple body. The compounds thus formed are frequently called oxides, sometimes acids, and sometimes bases or alhalies.

Oxygen gas is not sensibly absorbed by water. Water previously boiled has been shown by Dr Henry to be capable of absorbing 3∙55 percent, of its volume of oxygen gas.

In the subsequent part of this article the weight of an atom of oxygen will be considered as 1. A. volume of oxygen gas is equivalent to two atoms, provided we suppose water to be a compound of one atom of oxygen and one atom of hydrogen.

Sect. II.— Of Chlorine.

This substance, which is also a gas, was discovered by Scheele, and an account of it published in the Memoirs of the Stockholm Academy of Sciences for 1774. He gave it the name of dephlogisticated muriatic acid. The French chemists, in consequence of the experiments of Berthollet, gave it the name of oxygenized muriatic acid, which was afterwards contracted into oxymuriatic acid. The term cldorine, by which it is at present known, was applied to it by Davy in 1810, when he showed it to be a simple substance.

It may be obtained by putting a quantity of gray oxide of manganese in fine powder into a retort, and then pouring over it the muriatic acid of commerce. An effervescence takes place, and a yellowish green coloured gas is extricated, which may be received in glass phials previously filled with water, and having their heads sunk into a small water trough. When the gas ceases to come over, the extrication will be renewed by heating the mixture in the retort.

Chlorine has a yellowish-green colour, and a strong suffocating smell similar to that of aqua regia. It has also a pretty strong astringent taste.

Its specific gravity is 2∙5, if we reckon that of air unity. It refracts light very powerfully. If the refracting power of light be one, that of chlorine gas, according to Dulong, is 2 - 628∙

It has the property of destroying vegetable colours, and of rendering vegetable bodies exposed to its action white. This property has occasioned the introduction of chlorine into the process of bleaching. See the article Bleaching in this Encyclopaedia.

A lighted taper plunged into chlorine gas burns with a low red flame, giving but little light, but emitting a great deal of smoke. But several metals, as antimony and arsenic, take fire of their own accord when thrown into it. This is the case also with phosphorus, which first melts, and then burns with a low greenish-yellow flame. No animal can breathe this gas without suffocation.

When exposed to a pressure of about four atmospheres, and at the same time cooled, it is condensed into a liquid, as was first observed by Faraday. In this state it is a limpid yellow-coloured fluid, exceedingly volatile. Its specific gravity is very nearly 1∙33, its refracting power is less than that of water. It is a non-conductor of electricity.

Water, according to Dalton, absorbs twice its volume of this gas. It acquires a greenish-yellow colour, and the smell and properties of chlorine. When water thus impregnated is kept for some time in a temperature as low as 36°, crystals in plates, of a lively yellow colour, are formed. The specific gravity of these crystals at 32° is 1∙2. They have been shown by Faraday to be composed of
[table]

They constitute therefore a decihydrate of chlorine.
[7:6:360]

Chlorine combines with oxygen in four different proportions, and forms four compounds, which deserve to be described.

1. When a current of chlorine gas is passed, through a solution of carbonate of potash, an effervescence takes place, and small crystals in plates are deposited, to which the name of chlorate of potash has been given. This salt is a compound of chloric acid and potash. It possesses many properties similar to those of saltpetre, though it acts as a supporter of combustion with much greater vigour. If 15 , 5 parts of chlorate of potash be heated to incipient redness, the salt melts, and effervesces violently, giving out six parts by weight of pure oxygen gas, and leaving 9∙5 parts of the salt called chloride of potassium. Chloride of potassium is composed of
[table]

Hence it follows that chlorate of potash is composed of
[table]

But 5 potassium + 1 oxygen constitute 6 potash. We may therefore say that the constituents of the salt are,
[table]

The chlorine and the oxygen in the salt are united together, and constitute chloric acid. This acid may be obtained in a separate state, or at least in solution in water. The method is, to prepare chlorate of barytes, and to add to the solution of it in water dilute sulphuric acid as long as any precipitate continues to fall. Decant off the pure liquid. It is water holding chlorine acid in solution. It has no sensible smell nor colour, and reddens vegetable blues. When concentrated by evaporation, it has some» thing of an oily consistency. When heated, it is partly volatilized and partly decomposed. It is composed of
[table]

2. If chlorate of potash be put into a small flask or re- • tort with a sufficient quantity of dilute muriatic acid, and a very moderate heat be applied, a gas gradually escapes, which may be collected over mercury. This gas (the euchlorine of Davy) is the protoxide of chlorine. It has a much more intense greenish-yellow colour than chlorine. Its smell has some resemblance to that of burnt sugar. It does not act upon mercury, though chlorine rapidly combines with that metal. When moderately heated, it explodes very feebly, and five volumes of it become six, and these consist of four volumes of chlorine and two volumes of oxygen gas. We see from this that the constituents of this gas are,
[table]

Hence the gas is composed by weight of
[table]

3. When chlorate of potash is mixed with sulphuric acid, and made into small balls about the size of a pea, if we expose these balls to a heat somewhat lower than that of boiling water, a bright yellowish-green gas separates, which may be received over mercury. Its smell is peculiar and aromatic, and it has a colour still more intense than that of protoxide of chlorine. Water absorbs at least seven times its volume of it. The solution is deep yellow, and has an astringent and corrosive taste, leaving a disagreeable and lasting impression on the tongue. It does not act on mercury, but it destroys vegetable blues. When heated to 212° it explodes and increases in volume. It is now decomposed, and the gaseous mixture remaining is, according to the best experiments, a mixture of one volume chlorine and four volumes oxygen. Hence its constituents are,
[table]

Thus this compound consists in weight of
[table]

It has been called quateroxide of chlorine, but it is more probably a teroxide. It has been supposed by some to possess acid properties, and has therefore been called chlorous acid. But this is only as yet an hypothesis.

4. When quateroxide of chlorine is extricated from the mixtures of sulphuric acid and chlorate of potash, a peculiar salt is formed, which remains behind in the retort. We obtain this salt best when we use three or four grains of strong sulphuric acid for every grain of chlorate of potash. After the first violent action of the acid is at an end, heat is to be applied and continued till the yellow colour of the mass disappear. If we dissolve this residue in water, and crystallize, we obtain two salts, namel; 7 , bisulphate of potash, and a salt to which the name of perchlorate of potash has been given. It is quite neutral, is not altered by exposure to the air, and has a weak saline taste, lt is pretty soluble in boiling water, but very little soluble in cold water, and quite insoluble in'alcohol. Its crystals are elongated octahedrons. When heated to the temperature of 412° it gives out abundance of oxygen gas, while chloride of potassium remains. According to the experiments of Count Von Stadion, 17∙5 parts of it, when thus treated, give out 8 parts of oxygen, while 9∙5 of chloride of potassium remain. Hence the constituents of the salt are,
[table]

In the salt the 4 ’ 5 chlorine and 7 oxygen are united together, constituting perchloric acid; which is therefore a compound of 4*5 chlorine and 7 oxygen.

We may exhibit the constituents of these oxides of chlorine in the following table:
[table]

If 1 denotes-an atom of oxygen, it is evident that 4 ’ 5 must be the weight of an atom of chlorine; so that these bodies are compounds of an atom of chlorine with 1, 3, 5, 7 atoms of oxygen respectively.
[7:6:361]

Sect. III.— Of Bromine.

This substance was discovered by Balard of Montpellier, who investigated its properties, and made it known to the public on the 3d of July 1826. It was obtained by him from the mother water of the brine springs in the neighbourhood of Montpellier. It is a constituent of brine springs in general, and also of sea-water.

Balard’s process was as follows. A current of chlorine gas is passed through the liquid containing it, taking care not to add too much. A quantity of sulphuric ether is now poured on the liquid in a phial, taking care that the phial is completely filled. The two liquids being agitated together, are then left in a state of rest. The ether swims on the top, having acquired a fine hyacinth colour by dissolving the bromine. Agitate the ether with a strong solution of caustic potash. A salt is formed, which crystallizes in cubes. It is a bromide of potassium. Reduce these cubes to powder, mix them with gray oxide of manganese in powder, and dilute sulphuric acid, and distil. Red vapours rise, which condense in drops on the beak of the retort, and fall to the bottom of the receiver. This liquid is bromine.

Bromine has a brownish-red colour, so intense as to appear opaque. Its smell is very disagreeable, and has some resemblance to that of protoxide of chlorine, but is stronger and more suffocating.

Its taste is sharp and strong; and when taken internally, it acts as a violent poison. It acts with energy upon organic bodies, and particularly on the human epidermis, which it corrodes, giving it a yellow tinge.

Its specific gravity is 2∙96. It remains liquid at zero, but becomes solid and brittle at — 4 degrees. It is very volatile, and boils when heated to 116⅜ degrees. The specific gravity of its vapour is probably 5∙5555, that of air being unity. It is a non-conductor of electricity. A taper is extinguished when plunged into its vapour; but several of the metals burn brilliantly when they come in contact with it.

It destroys vegetable colours almost as powerfully as chlorine itself. It is slightly soluble in water, communicating a yellow colour to that liquid. It is more soluble in alcohol, and much more soluble in sulphuric ether; olive oil acts on it slowly. It is insoluble in sulphuric acid. When dropt into a solution of starch, it communicates a fine yellow colour.

Its atomic weight, from the experiments of Balard, Liebig, and Berzelius, appears to be ten.

It unites with oxygen, so far as is known, only in one proportion, forming a compound to which the name of bromic acid has been given. When bromine is agitated with a sufficiently concentrated solution of potash, two compounds are formed; namely, hydrobromate of potash, or bromide of potassium, which remains in solution; and bromate of potash, which being very little soluble in water, precipitates in a white crystalline powder. We may form bromate of barytes by agitating chloride of bromine in a concentrated solution of barytes. The bromate of barytes precipitates in the state of a whole powder. By solution in boiling water it may be obtained in acicular crystals. These crystals may be dissolved in hot water, and the barytes thrown down by dilute sulphuric acid. What remains is bromic acid held in solution by water.

By gentle evaporation, a part, but not the whole, of the water can be driven off. A syrupy liquid remains, which reddens litmus paper, and then discolours it. It has little smell; the taste is acid, but not caustic. When bromate of potash is heated it gives out oxygen gas, and is converted into bromide of potassium. From the experiments of

Balard, there is reason to conclude that bromic acid is a compound of
[table]

We are acquainted at present with only one compound ∣ of chlorine and bromine. It is a very volatile liquid, which 1 may be formed by passing a current of chlorine gas through bromine, and condensing the vapour formed, by passing them into a receiver, surrounded by a mixture of snow and salt. .It has a reddish yellow colour, a strong disagreeable smell, and a strong taste. It is very fluid, and very volatile. Metals plunged into it become incandescent, and are converted into chlorides and bromides. It dissolves in water. When potash is added to the aqueous solution, the chloride is decomposed, and an alkaline bromate and muriate is formed. No attempt has yet been made to analyse this chloride.

Sect. IV.— Of Iodine.

This substance was discovered in the year 1811, by M. Courtois, a saltpetre manufacturer near Paris. Its properties were first investigated by Gay-Lussac and Sir H. Davy.

It is obtained from help by the following process: The kelp is lixiviated with water till every thing soluble is taken up; the liquid is concentrated till all the crystals which it can be made to deposit are separated. The liquid is now mixed with sulphuric acid, and boiled for some time, till all the muriatic acid is expelled. Gray oxide of manganese being now added, the whole is put into a retort or stoneware still, with a glass capital, and heat is applied. Violetcoloured vapours pass into the receiver, and are condensed: these constitute iodine.

Iodine thus obtained is a solid substance of a grayish-blue colour, and something of the metallic lustre. It is usually in scales, but may be crystallized in octahedrons, similar to the primary form of sulphur. Its specific gravity is 3∙0844. It has a disagreeable smell, similar to that of chlorine, but not nearly so strong. Its taste is acrid and hot, and it continues for some time in the mouth. It possesses poisonous properties. It is strongly stimulating, and has of late been much employed as a medicine.

It destroys vegetable colours, but with less intensity than chlorine. It melts when heated to 2241 degrees, and is volatilized under the common pressure of the atmosphere when heated to 3511 degrees. Its vapour has a beautiful violet colour, and hence the name iodine (yωbrf). The specific gravity of this vapour is 8∙8.

It is very slightly soluble in water, but more soluble in alcohol and ether. It gives a blue colour when it comes in contact with the solution of starch in water, or indeed with starch in almost any state.

From the experiments of Dr Thomson and Professor Berzelius, the atomic weight of iodine appears to be 15∙75.

Iodine combines with oxygen, chlorine, and bromine, and forms compounds which deserve to be noticed.

1. Iodic acid, as the combination of iodine and oxygen is called, may be obtained in the following way: Put forty grains of iodine into a thin long-necked receiver; and into a bent tube shut at one end put 100 grains of chlorate of potash, and pour over it 400 grains of muriatic acid, of the specific gravity 1*105; then introduce the point of the bent tube into the receiver, and apply a gentle heat to it; protoxide of chlorine is generated. As soon as it comes in contact with the iodine, a combination takes place, and two new substances are formed; 1, a compound of iodine and chlorine; 2, a compound of iodine and oxygen. When heat is applied to the mixture, the first of these compounds is volatilized, and the last remains, [7:6:362] constituting iodic acid. It is a white semi-transparent solid, without smell, but having a strong astringent sour taste. When heated to a temperature somewhat higher than that at which olive oil boils, it is decomposed, being converted into iodine and oxygen. From the experiments of Davy, it appears to be composed of
[table]

It is very soluble in water, and when exposed to a moist atmosphere it gradually deliquesces.

Mr Connell of Edinburgh has lately discovered that this acid may be formed by digesting nitric acid on iodine till the whole is dissolved.

According to Sementini of Naples, there exists another compound of iodine and oxygen, containing less oxygen than iodic acid, and to which he has given .the name of iodous acid. It may be obtained by triturating together equal parts of iodine and chlorate of potash. When this mixture is exposed in a small retort to a spirit lamp, yellow fumes may be distilled over. They condense into a yellow fluid constituting iodous acid.

2. The compound of chlorine and iodine has received the name of chloriodic acid. It is easily formed by passing a current of chlorine gas into a vessel containing iodine. It is a yellow-coloured volatile body, which deliquesces when exposed to the air. Its solution in water possesses acid properties. It would appear probable, from the experiments of Davy, that it is a compound of
[table]

3. Bromine and iodine seem to be capable of uniting in two proportions. When the two bodies are placed in contact in certain proportions, we obtain a solid compound, which, when heated, gives out reddish-brown vapours, condensing into small crystals of the same colour, and resembling fern leaves in appearance. A newaddition ofbromine transforms these crystals into a liquid, resembling hydriodic acid, containing a great excess of iodine. This liquid bromide is soluble in water, to which it communicates the property of destroying the colour of litmus paper without reddening it.

Sect. V.— Of Fluorine.

[ The mineral called fluor spar, or Derbyshire spar, is common in lead mines. It is translucent, crystallized in cubes or octahedrons, and is either colourless or tinged yellow, green, red, or violet. If a quantity of this stone be reduced to powder and put into a retort of lead or silver, after being made into a magma with sulphuric acid, and, after applying a leaden or silver receiver, heat be applied, there gradually passes over a colourless and very volatile liquid, which has received the name of fluoric acid.

It continues fluid at — 4°, and is still liquid at the tempe-ratureof60°. Its boiling point islow,buthas not been determined. When exposed to the air it smokes, and has a smell similar to that of muriatic acid. When as concentrated as possible, its specific gravity is P0609; but when united with a certain portion of water, its specific gravity becomes 1∙25. Its attraction for water is very strong. Its fumes are very deleterious when drawn into the lungs. When a drop of it falls on the skin it acts as a corrosive, and produces a sore which does not soon heal. It corrodes glass with great rapidity, combining with and carrying off the silica of the glass.

It was long the opinion of chemists that this acid is a compound or oxygen and an unknown combustible basis. But all attempts to obtain this basis having failed, Ampere suggested, in 1810, that it was probably a compound of hydrogen with an unknown supporter, to which the name of fluorine may be given. This opinion was taken up by Davy in 1811, and his experiments, though they have not demonstrated the truth of Ampere’s hypothesis, have rendered it at least exceedingly likely to be true. We may state here some of the strongest proofs of the hypothesis which Davy was able to adduce.

1. When fluoric acid and potassium are brought into contact, a violent action takes place; a solid white substance is formed, and a quantity of hydrogen gas is disengaged. In this case the probability is that the fluorine of the fluoric acid unites to the potassium, and forms the white salt, while the hydrogen is disengaged.

2. When potassium is heated in contact with sal ammoniac, chloride of potassium is formed, and a quantity of gas disengaged. This gas is a mixture of ammonia and hydrogen, and consists of two volumes of ammoniacal, and one volume of hydrogen gas. Now when fluate of ammonia is treated with potassium, a similar effect is produced. A white salt is formed, and a gas evolved consisting of a mixture of two volumes of ammoniacal and one volume of hydrogen gas. It is probable that the salt formed in this case is fluoride of potassium.

3. When fluoric acid is exposed to the action of galvanism, hydrogen gas is given out at the negative wire; and the positive wire, supposing it platinum, is coated with a chocolate powder. When muriatic acid is treated in the same way it is decomposed, its hydrogen being given off at the negative wire, while its chlorine unites with the positive wire. Is it not probable that the chocolate powder is a compound of fluorine and platinum?

It has been shown that the atomic weight of fluorine (supposing it to exist) must be 2∙25.

Such are the properties of the supporters of combustion. They seem capable of uniting with every one of the other simple bodies. By uniting with one set they constitute acids ; by uniting with another they constitute alhalies or bases. Those acids and bases containing the same supporter are capable of uniting with each other, and of forming salts without decomposition. But when an acid containing one supporter is brought into contact with a base containing another supporter, it is more rarely that they combine. Much more frequently they mutually decompose each other. Thus there exist oxygen acids, chlorine acids, bromine acids, iodine acids, and fluorine acids; and the same number of sets of bases.

The atomic weights of the supporters are as follows:—
[table]

Chlorine is just double the weight of fluorine, and iodine just seven times the weight of the same atom.

It is probable that fluorine is still more negative than even oxygen, which excels all other supporters in this respect. But as fluorine has not yet been obtained in a separate state, our conclusions can only be supported by conjectures and analogy.

CHAP. II.—OF THE SIMPLE ACIDIFIABLE BASES.

The simple acidifiable bases at present known are the following :—
[table]
[7:6:363]

The first two of these bodies, hydrogen and azote, are gases which have never been reduced to a liquid or solid state. Carbon, boron, and silicon, are black powders, which have never been melted nor volatilized. Phosphorus, sulphur, and selenium, are solids easily fused and volatilized by heat. Arsenic, antimony, and tellurium, arc metals easily fused and voJatilized. The remaining seven bodies are difficultly fusible metals, which have been hitherto reduced to the metallic state only in minute quantities.

Sect. I.— Of Hydrogen.

Pure hydrogen can scarcely be said to exist in an isolated state; but it constitutes one of the ingredients of water, from which it may be disengaged by simple processes. Its properties were first investigated by Cavendish in 1766. It maybe obtained by dissolving zinc or iron filings in dilute sulphuric acid in a flask or small retort. An effervescence takes place, and hydrogen is evolved. It may be received in glass jars filled with water, and inverted on the shelf of the water-trough.

The gas, when pure, is colourless, and destitute of taste or smell. But it usually has a bituminous and disagreeable smell, which is very strong when we employ cast-iron turnings to procure it.

It is the lightest body with which we are acquainted, its specific gravity being only 0∙0694, that of air being 1. So that oxygen gas is sixteen times as heavy as hydrogen gas. In consequence of this lightness it is employed to elevate air-balloons.

It refracts light much more powerfully than any other gaseous body, if we take into account its small specific gravity; for if the refracting power of air be one, that of hydrogen gas is 0∙470, as determined by Dulong. It has a great effect in blunting the sound of sonorous bodies struck in an atmosphere of this gas. It is well known that sound moves at least thrice as fast in this gas as it does in common air.

Burning bodies plunged into it are immediately extinguished. Animals, when obliged to breathe it, soon die, precisely as if they were plunged into water. When a mixture of oxygen and hydrogen gases is made in the same proportion as in common air, hydrogen being substituted for azote, animals breathe it with impunity. But Messrs Allen and Pepys observed, that when animals are put into such an atmosphere, they are thrown into a profound sleep.

A hundred cubic inches of water previously deprived of air by boiling were found by Dr Henry to absorb 1 ∙53 cubic inches of this gas.

When mixed with oxygen gas in the proportion of one volume of oxygen to two volumes of hydrogen, it burns with a loud explosion by an electric spark, or the contact of a red-hot wire. Mr Cavendish first ascertained that the product of this combustion is water; so that water is a compound of one volume of oxygen and two volumes of hydrogen gas, or, by weight, of oxygen eight, and hydrogen one.

If we mix a hundred volumes of air with forty-two volumes of hydrogen gas, and pass an electric spark through the mixture, a detonation takes place, and sixty volumes disappear. Now one third of this loss is oxygen. If we examine the residuary gas, we shall find no trace of oxygen in it. Hence it is evident that a hundred volumes of air contain just twenty of oxygen.

Water, or oxide of hydrogen as it might be called, is a transparent and colourless liquid, destitute of smell, and having but little taste. It freezes at 32°, and boils at 212°. Its density is greatest at the temperature of 39°. A cubic inch of water at the temperature of 62°, and when the barometer stands at thirty inches, weighed in air with brass weights, weighs 252∙458 grains. Hence at the temperature of 60° the weight of a cubic inch of water is very nearly 252∙5 grains.

A hundred cubic inches of air at the temperature of 60°, and when the barometer stands at thirty inches, weigh 31T446 grains. Hence it follows that water at that temperature and pressure is 8l0∙734 times heavier than air.

Water, if we are to judge from the combinations into which it enters, is a neutral body. It shows little tendency to combine with simple bodies, whether supporters or acid or alkaline bases. But it combines, and apparently with equal ease, both with acids and bases, though without disguising their peculiar properties, or neutralizing their energies. To these combinations the term hydrate was applied by Proust, which, though somewhat exceptionable, has been generally adopted. It is not easy to form an accurate idea of the way in which water unites with other bodies. The electric theory of combination will scarcely apply to it; or at least we cannot determine, except from analogy, whether it be positive or negative with respect to those bodies with which it unites.

Hydrogen is capable of uniting with another dose of oxygen, and of forming a new liquid compound, which has been distinguished by the name of deutoxide of hydrogen. It was formed by Thenard by dissolving peroxide of barium in dilute muriatic acid, and then precipitating the barytes by means of sulphuric acid. This process is repeated a number of times, and then the muriatic acid is removed by treating the liquid with sulphate, of silver. The sulphuric acid left by this process is removed by means of barytes. Nothing now remains but a mixture of water and deutoxide of hydrogen, which is put into the exhausted receiver of an air-pump over sulphuric acid. The water gradually evaporates, and leaves the deutoxide of hydrogen in a state of purity.

It is a liquid which has a specific gravity of 1∙453. It attacks, the epidermis almost instantly, and produces a prickling pain, the duration of which varies according to the quantity of liquid applied. It whitens the tongue, and thickens the saliva.

When deutoxide of hydrogen is left to itself, it undergoes spontaneous decomposition, oxygen gas being given out. When heated to 80° it is decomposed with a violent explosion, oxygen gas being evolved in great abundance. By collecting the gas thus driven off from a given weight of deutoxide, it has been shown that it contains twice as much oxygen as water does. It is therefore a compound of
[table]

If water be a compound of one atom of oxygen and one atom of hydrogen, and if the atom of oxygen be represented by unity, it is evident that the weight of an atom of hydrogen will be 0∙125. Water is a compound of
[table]

and its atomic weight is 1∙125. Deutoxide of hydrogen is a compound of
[table]

and its atomic weight is 2∙125.

Many substances, when placed in contact with deutoxide of hydrogen in the state of powder, have the property of decomposing it, and evolving oxygen gas. This is the case with charcoal, silver, platinum, gold, osmium, palladium, rhodium, and iridium. Lead, bismuth, and mercury exercise an action, slow at first, but gradually increasing [7:6:364] in energy. The oxygen is driven off, and the metals are not oxydized. Several bodies, as selenium, arsenic, molybdenum, tungsten, and chromium, are oxydized when placed in contact with deutoxide of hydrogen. Several of the metallic oxides absorb an additional dose of oxygen, while others drive off the second portion of oxygen from the deutoxide without any of it combining with them.

Hydrogen has the property of combining with chlorine, and of forming the very important chemical substance known by the name of muriatic acid. If equal volumes of chlorine and hydrogen gas be put into a glass tube, and exposed to the direct rays of the sun, an explosion takes place. If this mixture be put into an exhausted glass vessel, it will be found that after the explosion the two gases have disappeared, and a quantity of muriatic acid gas has come in their place, exactly equal to the volume and weight of the two gases. It follows from this that muriatic acid gas is a compound of one volume of hydrogen and one volume of chlorine gas united together, without any alteration in bulk. Hence, the specific gravity of muriatic acid gas is the mean between that of hydrogen and chlorine gases, or 1∙2847.

Muriatic acid, or hydrochloric acid as it is also called, is a gaseous body, invisible, and elastic like common air, and having a peculiar smell and a very sour taste. No combustible body will burn in it, and it destroys life instantly when any attempt is made to breathe it. It is composed of
[table]

and its atomic weight is 4∙625.

The combination of hydrogen and bromine is called hydrobromic acid. It may be obtained by mixing with sulphuric acid the cubic crystals mentioned when describing the process for obtaining bromine, and heating the mixture in a small retort, the beak of which is plunged into mercury. A gas comes over, which is hydrobromic acid. But this gas may be obtained in a state of greater purity by moistening bromide of phosphorus, and exposing it in a small retort to the heat of a lamp.

It is a colourless gas, having an acid taste, and smoking when mixed with atmospheric air. Water absorbs it abundantly, but it is not altered by standing over mercury. Tin, when heated in it, absorbs the bromine and leaves the hydrogen; so does potassium. By this process the volume of the gas is reduced to one half. Hence hydrobromic acid gas is a compound of equal volumes of hydrogen gas and bromine vapour united together without any alteration of volume. Its specific gravity is 2∙8125, and it is a compound of
[table]

and its atomic weight is 10∙125.

When chlorine gas is mixed with hydrobromic acid, the bromine is immediately precipitated in drops, and muriatic acid is formed equal in bulk to the original gas. But it is not decomposed by oxygen or iodine, even at a red heat. Neither is bromine capable of decomposing water, when the mixed vapours of the two liquids are passed through an ignited porcelain tube.

Hydrogen and iodine, when united together, constitute a gaseous substance, distinguished by the name of hydriodic acid. It may be obtained by mixing together four parts of iodine and one part of phosphorus, moistening the compound with water, and heating it in a small retort. The gas which comes over must be received over mercury. This gas is hydriodic acid.

It is colourless and elastic like common air, has a smell similar to that of muriatic acid, and a very acid taste. When left in contact with mercury, that metal absorbs the iodine and leaves the hydrogen. By this process the volume of the gas is reduced to one half. It is evident from this, that hydriodic acid gas is a compound of one volume hydrogen gas and one volume iodine vapour united together without any alteration of bulk. Hence its specific gravity is the mean of that of its two constituents, or 4*40972. It is a compound of
[table]

and its atomic weight is 15∙875.

Water absorbs this gas with avidity. When the solution is heated rather below 262°, the greater part of the water is driven off, and a liquid obtained having the specific gravity 1-7. At 262° it boils, and may be distilled over.

It is at present generally admitted by chemists that fluoric acid is a compound of fluorine and hydrogen, though hitherto it has been impossible to decompose it or obtain the fluorine in a separate state. The characters of this acid bear a strong analogy to those of muriatic, hydrobromic, and hydriodic acids. Hence it is not unlikely that it will be found a compound of
[table]

Such are the compounds which hydrogen forms with the supporters, so far as the subject has been investigated. The order in which they are decomposed by the supporters may be represented as follows:

Hydrogen. Fluorine. Chlòrine. Oxygen. Bromine. Iodine.

That is to say, hydriodic acid is decomposed by all the supporters except iodine; hydrobromic acid is decomposed by chlorine and oxygen, but not by iodine; water is decomposed by chlorine, at least when assisted by heat, but not by bromine or iodine. As to fluoric acid, it is not decomposed by any of the supporters, even when assisted by heat.

Sect. II.— Of Azote.

This gas, which constitutes so great a portion of the at-; mosphere, was first recognised as a peculiar substance in 1772 by Dr Rutherford, afterwards professor of botany in the University of Edinburgh. Being one of the constituents of air, it may be obtained by various processes. l.If we leave a stick of phosphorus in a jar of air inverted over water till it ceases to smoke, the residual gas, after being washed with water, is azote. 2. If we mix in a wide jar standing over water a hundred cubic inches of common air with eighty cubic inches of deutoxide of azote, a great diminution of volume takes place, and about eighty cubic inches of a gas remains, which is azote nearly in a state of purity. 3. If a small tubulated retort be filled with bleaching powder (or chloride of lime) brought to the consistency of cream by water, and pieces of sal ammoniac be put into the retort through the tubular mouth, a pretty strong effervescence takes place, and azotic gas is disengaged abundantly.

Azotic gas possesses the mechanical properties of com-1 mon air, and, like it, is destitute of colour, taste, and smell. Its specific gravity is 0∙9722. It refracts light rather [7:6:365] more powerfully than air. If we reckon the refracting power of air one, that of azotic gas is 1∙020, as determined by Dulong. It cannot be breathed by animals without suffocation. Animals obliged to breathe it die precisely as if they were plunged under water; hence the name azote, by which it was distinguished by the French chemists (from α and ζωf). No combustible will burn in it. It is not sensibly absorbed by water; but 100 volumes of water recently boiled were found by Dr Henry to absorb 1∙47 volumes of this gas.

It has doubtless the property of combining with all the supporters of combustion, though hitherto the subject has not been investigated successfully.

With oxygen it unites in no fewer than five proportions, constituting the five following compounds:

1. Protoxide of azote.

2. Deutoxide of azote.

3. Hyponitrous acid.

4. Nitrous acid.

5. Nitric acid.

The last of these compounds, nitric acid, exists in saltpetre, which is a compound of nitric acid and potash. This salt forms spontaneously in the soil of different countries. The presence of animal matters and of lime has been found to promote its formation. It is obtained in different countries, particularly in India, by lixiviating the soil, and evaporating the lixivium to dryness, or till crystals are deposited. These crystals are afterwards purified by a second crystallization.

When 12∙75 parts of pure saltpetre are mixed in a retort with 6425 parts of sulphuric acid of the specific gravity 1∙837, and heat is applied, a fuming liquid passes over into the receiver, which is m7rze acid. When thus obtained it is a yellowish red liquid, which has a peculiar smell, and smokes when it comes in contact with atmospherical air. When heated, a gaseous matter is driven off, and it becomes colourless like water. Its specific gravity, when as strong as possible, is said to be 1∙55. Its taste is intensely sour. When applied to any part of the body, it acts as an escharotic, and speedily produces a sore, by destroying the texture of the part. It is one of the most powerful and useful of all the acids. Its atomic weight is 6∙75, that of oxygen being considered as unity. It is by means of nitric acid that all the other compounds of oxygen and azote are obtained.

1. Protoxide of azote was discovered by Dr Priestley, and called by him dephlogisticated nitrous gas. It is most easily obtained by saturating nitric acid with ammonia, and evaporating the liquid to dryness. A fibrous deliquescent salt is obtained, known by the name of nitrate of ammonia. When this salt is heated in a small retort to about the temperature of 400°, it melts and effervesces, ŭnà protoxide of azote is given out abundantly.

This gas is colourless, and destitute of smell. It has a sweetish taste, and its specific gravity is 1∙5277. Water absorbs about three fourths of its volume of this gas. Its refracting power, according to Dulong, is 1∙710, if we reckon that of air unity.

It is capable of supporting combustion, and bodies burn in it with as much brilliancy as in oxygen gas. But the combustion lasts only for a very short time, and it does not begin unless the body be in the first place heated to whiteness. Animals arc capable of breathing this gas for a few minutes without inconvenience, as was first discovered by Sir H. Davy. The breathing of it sometimes produces feelings of intoxication, but they are not follow ed by that languor and debility which is a constant attendant of intoxication by ardent spirits.

It is not altered by exposure to light, or by any heat below ignition. When passed through a red hot tube, or when electric sparks are passed through it, decomposition takes place, and nitric acid is formed. When exposed to a pressure of fifty atmospheres at the temperature of 45°, it becomes liquid. In that state it is transparent and colourless, exceedingly volatile, and it does not become solid though cooled down to —10°.

When mixed with hydrogen gas, and an electric spark passed through the mixture, a detonation takes place, and water is deposited, while a quantity of azotic gas remains, just equal (supposing it dry) to the original volume of protoxide of azote present. 100 volumes of protoxide of azote must be mixed, for complete combustion, with 100 volumes of hydrogen. After the combustion there remains nothing but 100 volumes of azotic gas,^[3. The volume is 101*77 (supposing the thermometer at 60° and the barometer at 30 inches) of moist azotic gas, which is equivalent to 100 of dry. ] while the inside of the tube is moistened with water. The hundred volumes of hydrogen gas having been converted into water, required for complete combustion 50 volumes of oxygen, which must have existed in the gas. Hence 100 volumes of protoxide of azote are composed of 100 volumes azotic gas, and 50 volumes oxygen gas, united together, and condensed into 100 volumes; or, which is the same thing, of one volume of azotic gas and half a volume of oxygen gas condensed into one volume. Or by weight, of
[table]

If we reckon the atomic weight of oxygen one, and consider this gas as a compound of one atom oxygen and one atom azote, then an atom of azote will weigh 1∙75.

Charcoal, phosphorus, sulphur, &c. may be burnt in this gas, and the phenomena are similar to what takes place when hydrogen is burnt in it.

Protoxide of azote is probably a neutral substance, atleast we have no evidence that it possesses either acid or alkaline qualities; for it will not combine either with acids or bases.

2. When dilute nitric acid is put into a small retort or] flask, with some copper or mercury, it dissolves either of< these metals, an effervescence takes place, and a gas is extricated, which may be received in glass jars standing over water. This gas is deutoxide of azote, or nitrous gas as it was called by Dr Priestley, the original discoverer of it.

It is colourless and invisible, like common air. Whether it has any taste or smell cannot easily be determined, because, whenever it comes in contact with air, nitrons acid is formed, which communicates its peculiar odour to the gas. Its specific gravity is 1∙0416. If we reckon the refracting power of air one, that of this gas is 1∙03, according to D along.

It is not sensibly absorbed by water. When that liquid is freed from air by boiling, 100 volumes of it absorb five volumes of this gas.

When deutoxide of azote is mixed with common air or oxygen gas, red fumes of nitrous acid are produced, heat is evolved, and the volume of gas is diminished. This is owing to the union of the gas with oxygen, and the formation of acid fumes, which are absorbed by water. The proportion of the two gases which unite varies according to circumstances. If we make the mixture in a glass tube 0∙9 inch in diameter, then one volume of oxygen gas unites with two volumes of deutoxide of azote. When we put deutoxide of azote into a globular vessel, and let up [7:6:366] common air to it bubble by bubble, agitating after the addition of each bubble, then one volume of oxygen gas will be found to unite with four volumes of deutoxide of azote. All intermediate proportions between these two extremes may be made to unite by varying the circumstances.

À solution of green vitriol, or of chloride of iron, has the property of absorbing this gas slowly, while at the same time it acquires a dark brown colour, and becomes opaque. By this absorption the purity of the gas may be determined.

When electric sparks are passed through this gas it undergoes decomposition, being· converted into nitrous acid and azotic gas. When passed through an ignited porcelain tube, it undergoes the same decomposition.

Charcoal and phosphorus may be burnt in this gas. When charcoal is burnt in it, the bulk of the gas is not altered, but it is converted into a mixture of equal volumes of carbonic acid and azotic gas. Now carbonic acid gas contains its own volume of oxygen gas. Hence it is obvious that deutoxide of azote is a compound of one volume of azote and one volume of oxygen gas united together, without any alteration of volume; consequently its specific gravity is the mean of that of oxygen and azotic gases. It is composed, by weight, of azote 0∙9722 or 1∙75, oxygen l∙1111 or 2. If we reckon the atomic weight of azote 1∙75, this gas is obviously a compound of one atom azote and two atoms oxygen.

3. When deutoxide of azote is mixed with oxygen gas, bubble by bubble, in a wide glass vessel, four volumes of deutoxide combine with one volume of oxygen gas, and form an acid which is absorbed by the water. Now four volumes of deutoxide of azote consist of two volumes azotic and two volumes oxygen gas united together. It is clear, therefore, that the acid formed must be a compound of two volumes azotic and three volumes oxygen gas, or of one volume azotic and one and a half volume oxygen gas. This, by weight, constitutes azote 0∙9722 or 1∙75, oxygen 1∙6666 or 3. If we reckon the atomic weight of azote 1∙75, we see that the acid formed in this case is a compound of one atom of azote and three atoms of oxygen.

This acid has received the name of hyponitrous. It can exist only in combination. All the salts formerly called nitrites are in fact combinations of this acid with a base. Hyponitrous acid readily combines with bases, and forms a genus of salts to which the name of hyponitrites has been given. When we attempt to separate the acid from any of these salts, it is immediately resolved into nitrous acid and deutoxide of azote. Hyponitrous acid is always formed whenever deutoxide of azote is left in contact with a powerful base.

4. If we take a quantity of pure crystallized nitrate of lead, and, after drying it for some timeat the temperature of 300°, reduce it to powder and put it into a small bottle-glass retort; when heated almost to redness an acid liquid comes over, which must be collected in a receiver surrounded by a mixture of snow and salt. This acid has received the name of nitrous.

It is a liquid of an orange-yellow colour, has a caustic taste, a very strong smell, and a specific gravity of 1 ’ 451. It boils at 82° ∙5, and assumes the form of an orange-red vapour. Water decomposes it instantly, and converts it into nitric acid and deutoxide of azote. It does not seem capable of combining with bases; hence no such genus of salts as nitrites exist. Dulong analysed it by passing it through red-hot copper turnings. Azotic gas was driven off, and the copper was oxydized. From this analysis it appears that it is a compound of one volume azotic and two volumes oxygen gas. Hence its constituents by weight are, azote 0∙9722 or 1∙75, oxygen 2∙2222 or 4. So that (supposing an atom of azote to weigh 1∙75) it is a compound of one atom azote and four atoms oxygen.

5. It has been ascertained by experiments that appear decisive, that nitric acid is a compound of one volumeazotic and two and a half volumes oxygen gas. Hence its constituents by weight are, azote 0∙9722 or 1∙75, oxygen 2∙7777 0 r 5. Hence it is a compound of one atom azote and five atoms oxygen.

Such are the poperties and constitution of the compounds of azote and oxygen. If we consider the constituents as in the gaseous state, their relative proportions will be as follows:
[table]

If we take the weights of the constituents only int view, the constituents of these compounds will be reprc sented as follows:
[table]

It is obvious that 1∙75, or some multiple or submultiple of that number, represents the atomic weight of azote.

Chemists are not quite agreed about the atom of azote. The difference of opinion depends upon the view taken of the constitution of water. Those who consider water as a compound of one atom hydrogen and one atom oxygen, draw, asa necessary consequence, that half a volume of oxygen is equivalent to an atom, while a whole volume of most other gases represents an atom. Those who have adopted this opinion represent the atom of azote by 1∙75. But those chemists who consider water as a compound of two atoms hydrogen and orie atom oxygen, naturally deduce the number of atoms in each compound from the number of volumes of each constituent. Deutoxide of azote being a compound of one volume of each constituent, they consider it as a compound of one atom of azote and one atom of oxygen. Hence the atomic weight of azote will be O∙875, and the composition of the various compounds will be as follows:
[table]

It would be premature to say that the truth of either of these views can be demonstrated; but the first of the two is the simplest, and has been generally adopted by British chemists.

Azote has the property of combining with chlorine, and of forming a very singular compound, first noticed by Dulong, to which the name of chloride of azote has been given.

To procure it, dissolve a quantity of nitrate of ammonia in water of the temperature 110°, put the solution into a flat dish, and invert over it a phial or cylindrical glass jar, previously filled with chlorine gas. The chlorine is slowly absorbed. A yellowish oily looking matter collects on the surface of the liquid within the jar, and gradually falls to the bottom. This is the chloride of azote. It is so formidable a compound, that experiments on it should be made upon a very small scale.

Its colour is similar to that of olive oil. Its smell is peculiar and strong. It is very volatile, and is soon dissipated when left in the open air. It may be distilled over at [7:6:367] 160°, but when heated to 212° it explodes with prodigious violence. In a vacuum it is converted into vapour, which is again condensed into a liquid when the pressure of the atmosphere is restored. If this vapour be heated sufficiently, it explodes with as much violence as the liquid itself. The specific gravity of this liquid is 1∙653. It does not become solid though exposed to the cold produced by a mixture of ice and chloride of calcium. When it comes in contact with phosphorus or oils, a violent detonation takes place. The effect is so instantaneous and so great that it has been impossible to collect the products.

When chloride of azote is brought in contact with copper, azotic gas is disengaged, and there is formed a solution of chloride of copper. This shows that the substance is a compound of azote and chlorine. Davy, from decomposing it by mercury, concluded that it is composed of one volume azotic and four and a fourth volumes chlorine gas. Probably it is in reality a compound of one volume azotic and five volumes chlorine gas. This would be equivalent to
[table]

The bromide of azote is still unknown; but Μ. Courtois discovered an iodide of azote, which may be prepared in the following manner: Put a quantity of iodine, in powder, into a solution of ammonia in water. It is converted into a brownish black matter, which is iodide of azote. While still moist, the whole may be thrown on a filter, to allow the ammoniacal liquid to pass through. While the iodide is still moist, the filter should be stretched on a board, and fixed firm to it by means of a little paste or mucilage; for the powder, when dry, detonates violently upon the smallest agitation. If potash solution or hydriodate of ammonia be poured upon it, azotic gas is evolved, and the iodide is decomposed. Even water occasions a slow evolution of azotic gas. The iodide detonates with great violence when slightly touched or when heated. The only products are azotic gas and iodine. These are of course its constituents, but it has not been possible to determine the proportions in which they are united.

Azote is capable likewise of combining with hydrogen, and of forming an important compound called ammonia. Ammonia may be obtained in the state of gas by means of the salt called sal ammoniac, which is a compound of muriatic acid and ammonia. Introduce into a small retort about half an ounce of sal ammoniac, previously reduced to powder; reduce about half an ounce of unslaked quicklime to powder, and introduce it into the same retort. Shake, them well so as to mix them together; then fill the whole belly of the retort with unslaked lime in powder. Plunge the beak of the retort under mercury, and apply the heat of a lamp. Ammoniacal gas is disengaged abundantly, and must be received in glass jars standing over mercury.

Ammoniacal gas is colourless, and possesses the mechanical properties of air. Its smell is strong, pungent, and quite peculiar. Its taste is acrid and caustic, and when drawn into the mouth it destroys the cuticle. It cannot be breathed, nor even drawn into the lungs. Its specific gravity is 0∙59027. If we reckon the refracting power of air 1, that of ammoniacal gas is 1∙309, according to Dulong. It converts vegetable blues into green.

When this gas is subjected to a pressure of six and a half atmospheres at the temperature of 50°, it is condensed into a colourless fluid, having a greater refracting power than water, and a specific gravity of 0∙76.

Water absorbs 780 times its volume of this gas, and acquires the smell and properties of ammonia. In this state it is employed for chemical purposes. It is specifically lighter than water, and it is lighter in proportion to the quantity of gas which it contains. The following table by Dalton exhibits the specific gravity, the boiling point, and the quantity of ammoniacal gas, in liquid ammonia, from the strongest to the weakest.
[table]

When electrical sparks are passed through ammoniacal gas, it is slowly decomposed, its volume is doubled, and the gaseous matter into which it is converted is found to be a mixture of one volume of azotic and three volumes of hydrogen gas. It is clear from this that ammonia is a compound of one volume azote and three volumes hydrogen united together and condensed into two volumes; or, which is the same thine, it is composed of
[table]

So that its atomic weight is 2∙125. Its specific gravity must be obtained by adding together the specific gravity of three volumes of hydrogen and one volume of azotic gas, and dividing the same by two, because these volumes in the gas are reduced to half their natural bulk.
[table]

of ammoniacal gas.

Ammoniacal gas, when mixed with oxygen gas, may be detonated by electricity. When chlorine and ammonia are mixed in the gaseous state, a sudden combustion and detonation takes place. The chlorine unites with the hydrogen of the ammonia, and forms muriatic acid, while the azote is disengaged in the state of gas. The muriatic acid formed combines with a portion of ammonia, and forms sal ammoniac.

Ammonia possesses the characters of an alkali very decidedly. It neutralizes acids and forms salts, many of which are known, and of considerable importance.

The union of the different bodies with azote cannot be considered as very intimate; for they can all be destroyed by the application of a sufficiently strong heat. In this respect they differ exceedingly from the compounds of hydrogen.

Sect. III.— Of Carbon.

Carbon exists in immense quantity in the vegetable kingdom[7:6:368], and is easily obtained by heating to redness woods in close vessels, in a state of greater or less purity. It exists likewise in the earth in two distinct states, which are distinguished by the names of anthracite and plumbago. It occurs crystallized and transparent, when it is distinguished by the name of diamond.

There are two varieties of wood charcoal. If the wood be not heated to ignition, but only till all vapours cease to be emitted, we obtain a black shining mass, having the shape of the pieces of wood employed, but much lighter. Charcoal made in this way burns with some smoke and flame. It is a non-conductor of electricity, and cannot be employed as one of the elements of the galvanic pile. It is a very bad conductor of heat.

If the heat be raised to redness, and kept at that point till all smoke and vapour cease to be emitted, the charcoal obtained is black, and, like the former, retains the shape of the pieces of wood employed. It is an excellent conductor of electricity, and may be substituted for one of the metals in the galvanic pile. It is also a good conductor of heat, and not nearly so combustible as the first species of charcoal.

Charcoal is insoluble in water; it is destitute of taste and smell, and may be exposed to the most violent heat that we can raise in close vessels without alteration. It does not putrefy, like wood. It has the curious property of absorbing bad smells from cloth when wrapt up in them. New-made charcoal absorbs moisture with avidity. It also absorbs gases, and many of them become much more condensed in the pores of the charcoal than in their natural state. This will be obvious from the following table by De Saussure, exhibiting the number of volumes of various gases absorbed by one volume of boxwood charcoal.
[table]

Charcoal appears light, and sometimes even swims on water; but when allowance is made for the cells which it contains, the real specific gravity is very nearly 3 ’ 5.

Well-burnt charcoal consists almost wholly of carbon. There is present also a minute quantity of hydrogen, and a small quantity of earthy matter, which existed in the wood from winch the charcoal was made.

Anthracite, though it is most frequently found in the transition formation, sometimes likewise is met with in the common coal-beds. It is black, has a splendent lustre, and a specific gravity approaching to 1*5. It burns without flame, and consists chiefly of carbon. The same remark applies to plumbago, which is a soft mineral, having a greasy feel, the metallic lustre, and a colour approaching that of lead. Its specific gravity varies from 1∙9 to 2∙32. It is a conductor of electricity, and, when strongly heated, burns slowly, and without emitting any flame.

The diamond has been hitherto found only in the torrid zone, and the two known localities are India and Brazil. It is said to have been lately discovered in Siberia; but no accurate information on the subject has yet reached this country. It is usually white and transparent, has a splendent lustre, is crystallized in octahedrons, and has a specific gravity of 3∙52. It refracts light powerfully, and is a non-conductor of electricity. When heated to red ness in the open air, it consumes slowly without flame; but in a close vessel it withstands the most violent heat that can be applied, without undergoing any alteration.

Carbon combines with all the supporters of combustion, and likewise with hydrogen and azote. Let us take a view of these combinations.

I. There are three combinations of carbon and oxygen, ∣ namely, carbonic acid, carbonic oxide, oxalic acid. The first and third of these compounds possess acid properties;' but the second is neutral, or at least has not hitherto been observed to have any tendency to combine either with bases or acids.

1. When charcoal is burnt in a given volume of air,∣ though no smell is evolved, yet the nature of the air is soi much altered that animals can no longer breathe it without death. It was ascertained by Lavoisier, that in such cases of combustion the oxygen of the air is converted into carbonic acid, which is the substance that gives the air its suffocating properties. When charcoal is ignited in oxygen gas, the volume of the gas is not altered; but it is gradually converted into carbonic acid gas.

The easiest method of procuring carbonic acid is to put pure calcareous spar or chalk into a small retort or flask, and to pour over it muriatic acid previously diluted with water. The chalk dissolves, an effervescence takes place, and carbonic acid gas is disengaged abundantly. It may be received over water.

It is a colourless gas, possessing the mechanical properties of common air. When applied to the nose it excites a pungent sensation, similar to that produced by brisk beer. Its taste is that of a weak but distinct acid. Its specific gravity is 1∙5277. If the refracting power of air be 1, that of this gas is 1∙526, according to Dulong. It acts feebly upon vegetable blues. It gives a purple colour to litmus infusion, but has no sensible effect on water rendered blue by the juice of red cabbage. It cannot be breathed, nor even drawn into the lungs; the attempt is speedily followed by asphyxia and death, unless the animal be immediately removed into pure air.

No combustible will burn in it. A mixture of nine volumes air and one volume carbonic acid gas extinguishes a candle. Water absorbs about its own volume of this gas, and acquires a sour taste and the properties of a weak acid. When water thus impregnated is exposed to the open air, the carbonic acid speedily makes its escape.

When exposed at 32° to a pressure of thirty-six atmospheres, it is condensed into a liquid, which is colourless, very fluid and light, and which has a less refractive power than water. It may be passed through an ignited porcelain tube without alteration; but when electric sparks are passed through it for some time, it is probably decomposed into carbonic oxide and oxygen gas. When a mixture of equal volumes of this gas and hydrogen is passed through an ignited porcelain tube, the carbonic acid is converted into carbonic oxide and water. If we pass the gas through ignited charcoal, it will be converted into carbonic oxide, and its bulk will be doubled.

As oxygen gas is converted into carbonic acid without any alteration of bulk by burning in it charcoal or diamond, while these bodies disappear, it is obvious that this gas is a compound of oxygen and carbon. The proportion of the carbon may be learned by subtracting the specific gravity of oxygen gas from that of carbonic acid gas.
[table]

Hence carbonic acid is composed of oxygen 1∙1111 or 2, carbon 0 , 4166 or 0∙75. If we consider 0∙75 as denoting the atomic weight of carbon, then carbonic acid will be a [7:6:369] compound of one atom carbon and two atoms oxygen; and its atomic weight will be 2∙75.

As carbonic acid gas is formed by the breathing of animals and the combustion of wood and coal, it is not surprising that a portion of it should always exist in the atmosphere. The proportion varies somewhat, being diminished by rain and increased by dry weather. The mean bulk of this gas in 10,000 volumes of air is, according to Saussure, 4∙15 volumes. The greatest quantity observed by him was 5∙74 volumes, and the smallest 3∙15 volumes.

This gas combines with bases, and forms a genus of salts called carbonates. Like all weak acids, it unites in various proportions with most of the bases.

2. Carbonic oxide may be obtained by mixing equal weights of carbonate of lime or carbonate of barytes with iron filings, and exposing the mixture to a strong red heat in an iron bottle. A mixture of carbonic acid and carbonic oxide is extricated, the former of which may be removed by washing the gaseous product in milk of lime.

Carbonic oxide gas is colourless, and destitute of taste and smell. Its specific gravity is 0∙9722. Its refractive power is 1*157, that of air being 1. Water freed from air absorbs about yθth of its volume of this gas. No animal can breathe it, one or two inhalations producing asphyxia. It burns with a blue flame, and gives but little light. It explodes by electricity when mixed with oxygen gas. One volume of the gas requires for complete combustion half a volume of oxygen gas. The product is a volume of carbonic acid gas. It is clear from this that one volume of carbonic oxide gas contains just as much carbon as carbonic acid gas, but only one half the volume of oxygen gas. It is therefore composed of
[table]

and its atomic weight is 1∙75. We may consider carbonic acid gas as composed of
[table]

while carbonic oxide is composed of
[table]

Carbonic oxide gas combines with its own volume of chlorine, and forms a gas distinguished by the name of phosgene gas or chloro-carbonic acid. To form the compound, it is only necessary to expose the mixture to sunshine for a quarter of an hour.

3. Oxalic acid was discovered by Scheele. It may be formed by digesting sugar in nitric acid till all effervescence is at an end. On cooling, the liquid deposits crystals of oxalic acid in small prisms. When shavings of wood are mixed with caustic potash, and exposed to a heat considerably higher than that of boiling water, the wood suffers decomposition, and is partly converted into oxalic acid. This is probably the mode taken by the manufacturers of oxalic acid in this country.

Oxalic acid crystallizes in small prisms. Its taste is intensely acid, and when taken internally, even in small quantities, it destroys life. When taken to the extent of about half an ounce it proves almost instantly fatal. It combines with bases, and forms a genus of salts called oxalates. Oxalate of ammonia is very much employed in chemical analysis to throw down lime, and to separate it from the other constituents of minerals which contain it. When oxalic acid is heated with concentrated sulphuric acid, it is converted into a mixture of equal volumes of carbonic acid and carbonic oxide. We see from this that the acid is a compound of
[table]

Hence its atomic weight is 4'5; and it is a compound of
[table]

II. Carbon and chlorine are capable of uniting in three different proportions, as was first ascertained by Mr. Faraday.

1. Sesquichloride of carbon. This compound was obtained by mixing together olefiant gas and chlorine gas, and exposing the mixture to sunshine. Muriatic acid gas was formed, which was absorbed by water; and more chlorine being introduced, the vessel was again exposed to sunshine. These processes were repeated till white crystals were deposited on the inside of the vessel containing the gases. These crystals constitute sesquichloride of carbon.

When pure it is a transparent colourless substance, with scarcely any taste, but having an aromatic odour bearing some analogy to that of camphor. Its specific gravity is 2. Its refractive power is nearly equal to that of flint-glass (1 ’ 5767). It is very friable, and is a non-conductor of electricity. Its crystals are usually six-sided prisms. It is not readily combustible. It is insoluble in water, but dissolves readily in alcohol, and still more easily in ether. It is scarcely acted on by acids or alkalies. It is not acted on by oxygen at temperatures below a red heat. It detonates by electricity when its vapour is mixed at once with oxygen and hydrogen gases. Mr Faraday has shown, from the quantity of chlorine and olefiant gas necessary to form it, that this substance is a compound of
[table]

so that its atomic weight is 7∙5, or ten times that of carbon.

2. Chloride of carbon. When sesquichloride of carbon is exposed to a red heat, it loses some chlorine, and is converted into a liquid to which the name of chloride of carbon has been given.

It is colourless and very fluid. Its specific gravity is 1∙5526. Its refracting power is 1∙4875, or very nearly that of camphor. It does not congeal at zero. Between 160° and 170° it is converted into vapour. It is insoluble in water, but dissolves in alcohol and ether. Oxygen decomposes it at high temperatures. From the analysis of Faraday, it appears to be a compound of
[table]

so that its atomic weight is 5∙25.

3. Dichloride of carbon. This is a solid white substance in feathery crystals, accidentally obtained by Μ. Ĵulin of Abo while distilling a mixture of nitre and sulphate of iron. From the analysis of Faraday and Philips, it appears to be a compound of
[table]

so that its atomic weight is 6.
[7:6:370]

III. Bromide of carbon may be formed by throwing sesquiodide of carbon upon bromine in a glass tube. The action is instantaneous, and two bromides are formed at once. Water dissolves the bromide of iodine, while the bromide of carbon remains in the state of a liquid at the bottom of the tube. It contains an excess of bromine, which may be removed by potash.

Bromide of carbon is a colourless liquid. It has an ethereal smell apd very sweet taste. By exposure to air it becomes red coloured. When heated at the flame of a candle it gives out red vapours of bromine, but does not burn with flame.

Bromine readily combines with olefiant gas when placed in contact with it. The compound is an aromatic liquid, volatile, and decomposed by a red heat. This compound has been called hydro-carburet of bromine.

IV. Carbon and iodine unite in two proportions, forming a sesquiodide and an iodide of carbon.

1. Sesquiodide of carbon. This substance is easily formed in the following manner. To an alcohol solution of io-dine add caustic potash till the colour is destroyed. Ą whitepowder consisting of iodate of potash falls. Distil with a very gentle heat the alcohol from the clear liquor. The sesquiodide of carbon is deposited during the process.

It is in small plates, opaque, and of a sulphur-yellow colour. It has a strong aromatic odour, like that of saffron. Its.taste has been compared to that of nitric ether. Its specific gravity is 2. When heated it melts, and if the heat be increased, iodine vapours rise, and carbon remains. It is insoluble in water, but dissolves readily in alcohol and ether. From the analysis of Serullas, it appears to be a compound of
[table]

so that its atomic weight is 24*375.

2. Iodide of carbon. This compound was obtaiped by Serullas by the following process. Equal weights of perchloride of phosphorus and sesquiodide of carbon are triturated together in a mortar. This mixture is put into a phial, into the mouth of which a bent tube is luted. Heat is applied to the-bottom of the phial, while the open end of the tube is plunged into a vessel filled with water. The heat must just be sufficient to melt the iodide of carbon. Some vapours of iodine first make their appearance, then a red liquid passes over and falls to the bottom of the water, where it speedily loses its colour. Iodine, chloride of iodine, and iodide, of phosphorus, remain in the phial. The liquid is separated from the water by means of a funnel, with a capillary tube. It is purified .by washing it in caustic potash. It is freed from hydrocarburet of chlorine by pouring on it about, five times its þulk of concentrated sulphuric acid, and stirring the mixture from time to time with a,glass rod. The hydrocarburet is destroyed, and the pure iodide of carbon collects at the bottom, being heavier than sulphuric acid.

It is a transparent light yellow liquid, having a peculiar and strong, ethereal smell. Its taste is very sweet, with a sensation of coolness analogous to that produced by mint. It does not become solid when cooled down to 32°. It is slightly soluble in water. It does not burn. When exposed to air it assumes a red colour. From the analysis of Serullas, it appears to be a compound of
[table]

so that its atomic weight is 16.5.

Faraday found that iodine and olefiant-gas combine, atom to atom, and form a white crystalline body, having an aromatic odour and a sweet taste.

V. Carbon and hydrogen have the property of combining with each other in a great variety of proportions, and of forming many compounds, all of which are remarkably combustible, and many of them are of great importance. We shall notice a few of the simplest of these compounds here.

1. Carburetted hydrogen. This gas may be collected pure, or nearly so, from a blower in a coal mine. It is formed also abundantly at the bottom of stagnant pools containing decayed vegetable matter during the summer season. When the bottom of the pool is stirred, abundance of gas is extricated, consisting of carburetted hydrogen, mixed with a little carbonic acid gas, and usually also with some atmospherical air.

It is a colourless gas, destitute of taste and smell. Its specific gravity is 0∙5555. Its refracting power is l∙504, that of air being unity. It cannot be breathed, the attempt bringing on instant asphyxia. It burns with a yellow flame, and gives a good deal of light. When mixed with aiŗ or oxygen gas in the requisite proportions, it detonates by the electric spark. For complete combustion, it requires twice its volume of oxygen gas, and produces exactly its own volume of carbonic acid gas. The only other product is water. Now, one of the volumes of oxygen gas went to the formation of carbonic acid gas, and it must have united with a volume of carbon vapour. The other volume of oxygen gas, in order to be converted into water, must have combined with two volumes of hydrogen gas. It is clear from this that a volume of carburetted hydrogen must contain
[table]

These three volumes, when condensed into one, make up exactly the specific gravity of carburetted hydrogen.

The atomic constitution of this compound must be
[table]

so that the atomic weight is unity.

When this gas is mixed with chlorine, no action takes place in the dark; but when exposed to the light, if the mixture be in contact with water, it is gradually converted into carbonic acid. That the decomposition may be complete, we must mix four volumes of chlorine with one volume of carburetted hydrogen. One volume of carbonic acid is formed, two volumes of water are decomposed, and four volumes of chlorine are converted into muriatic acid.

2. Olefiant, gas. This gas is evolved when a mixture of one part by weight of alcohol, and four parts of strong sulphuric acid, are heated in a retort. The gas evolved is invisible, and possesses the mechanical properties of air. It is destitute both of smell and taste. Its specific gravity is 0∙9722. Its refracting power is 2∙302, that of air being unity. It is unfit for inspiration, producing immediate asphyxia, as is the case with all gases containing carbon as a constituent.

When electrical sparks are passed throuth it, the volume of the gas increases, and carbon is thrown down. It is said that in this way the whole carbon bay be thrown down, and the gas converted into pure hydrogen. Were this done, the volume of the gas would be just doubled. Olefiant gas burns with great splendour, and detonates very loudly when electrical sparks are passed through a mixture of it with oxygen gas in the requisite proportions. For complete combustion, one volume of the gas must be [7:6:371] mixed with three volumes of oxygen gas. The products are two volumes of carbonic, acid gas, and a quantity of water. Two volumes of the oxygen gas went to the formation of carbonic acid gas; the other volume formed water by uniting with two volumes of hydrogen gas. From this it is .clear that a .volume of olefiant gas is a compound of ,
[table]

These four volumes, added together, just make up the specific gravity of olefiant gas.

The atomic constitution of the gas is obviouslv
[table]

so that its atomic weight is 1∙.75, or the same as that of azote. It differs from carburetted hydrogen by containing an additional dose of carbon.

Olefiant gas and chlorine gas, when placed in contact, unite in equal volumes, and form a colourless transparent fluid, having an agreeable smell, and a sweetish, sharp, agreeable taste. It has a specific gravity of 1∙22, and boils at. 152°. At 49° its vapour is capable of supporting a column of mercury of 24∙66 inches in length. The specific gravity of this vapour is 3∙4722, showing that it is a compound of one volume of olefiant gas and one volume of chlorine gas united together and condensed into one volume. Hence its atomic weight is 6∙25. This liquid has received the name of liydrocarburet of chlorine. It burns with a green flame, giving out copious fumes of muriatic acid and much soot.

3. Carbo-hydrogen. When one part of pyroxylic spirit, The nature and history of this spirit will be given in a subsequent part of this article. three parts of muriatic acid, and one part of nitric acid, arc heated in a flask, an effervescence takes place, and a gas is extricated which must be received over mercury. This gas is transparent and colourless, has a pungent and disagreeable smell, and burns with a lively bluish-white flame. Water absorbs five times its volume of this gas, and oil of turpentine absorbs thirty times its volume of it; but it is neither absorbed by acids nor alkalies. It consists of a mixture of about eight volumes of azotic gas, sixty-three volumes of deutoxide of azote, and twenty-nine volumes of an inflammable gas, to which the name of sesquichloride of carbo-hydrogen may be given, as, according to the analysis of Dr Thomson, it is a compound of
[table]

so that its specific gravity is 4∙2361. Its basis is a gas composed of one volume of carbon vapour and one volume of hydrogen gas condensed into one volume; so that its specific gravity is 0∙4861, and its atomic weight 0∙875, or just one half of that of olefiant gas·^[5. The paraffine of Reichenbach, which is a solid crystalline substance has been shown by Jules Gay-Lussac to be a compound of one atom hydrogen and one atom carbon. It is therefore connected with carbo-hydrogen. ]

4. Superolefiant gas. When whale oil is exposed to an incipient red heat, it is converted into a gas which burns with a beautiful and very strong light, and which has been proposed as a substitute for coal gas for illuminating the streets, &c. .Mr Dalton, in examining this gas, found that it contained a portion of gaseous matter, one volume of which required for complete, combustion 4∙5 volumes of oxygen gas, and formed three volumes of carbonic acid gas. Hence it. follows 'that it is a compound of tljree volumes carbon vapour and three volumes hydrogen gas condensed into one volume. Iīenċe its specific gravity must be 1∙4583, and it must be composed of 1 < κ n>ibo) .ρ
[table]

Hence its atomic weight is 2∙625. This body was called superolefiant gas by Mr Dalton. But äs a ’ ‘Considerable number öfgaseS and vapours'áeėm to ekiśt, distinguished from each other merely by the number of atomè of carbon and hydrogen (both equal in number) contained in a volume, it becomes necessary to contrive a modé’of nstn-ing which may be extended’to any"number of these compounds.' The simple'compound of one volume ’ Carbon vapour and one volume hydrogen gas may be called carbohydrogen, and the others may be distinguished bŷ prefixing an abbreviation of the Greek numeral indićaíinġ the number of atoms conjoined in each volume. Thus a volume of 1 X J ʹ.i
[table]

At least three more of these compounds are at préàent known.

This view of the subject is not yet familiar to chemists; but it may ultimately throw much light' upon the nature of many vegetable substances which at present seem so mysterious. The ôĩls, for example,'though i they are all peculiar bodies, are cotnposed of carbon f and' hydrogen in nearly the same proportions. May not these diversities be partly accounted for by this groupingŉf the atoms to constitute an integrant particle of a mote or less complicated nature?

5. Tetarto-carbo-hydrogm. When oil gas is compressed, it is partially condensed into a transparent liquid of a light yellow tinge. Mr Faraday, by repeated distillations, separated this oily body into a variety of volatile oils, differing from each other in their volatility. One of these, at 6°, is a transparent colourless liquid; but when slightly heated, it begins to boil, and before it has reached the temperature of 32° it is all resolved into a vapour or gas, which burns with a brilliant white flame. Its specific gravity is 1∙9444. At zero it is again condensed into aliquid, whose specific gravity is only 0∙627 at the temperature of 54°. When this liquid is converted into a vapour, it increases in volume 261^∙ times. It is slightly soluble in water, and abundantly in alcohol and olive oil. One volume of the vapour of this oil requires for complete combustion six volumes of oxygen gas; water, is formed, and four volumes of carbonic acid gas. It is obvious from this, that a volume of the vapour contains '
[table]

Hence the specific gravity is'1∙9444. It is comooSed of
[table]

so that its atomic weight is 3∙5.

6. Bicarburet of hydrogm. A portion of the oil from condensed Oil gas, which boiled at 176°, was exposed to the cold of zero. It became partly* solid. Being subjected to pressure between folds of blotting paper, to separate [7:6:372] the liquid part as completely as possible, it was allowed to liquefy. It constituted a colourless transparent liquid, whose specific gravity at 60° was 0∙85. It crystallized when cooled down to 32°. The crystals melted at 42°. It contracted very much in the act of freezing, nine parts becoming eight. The specific gravity of its vapour at 60° is 2-7083. It is a non-conductor of electricity. It is slightly soluble in water, but very soluble in fixed and volatile oils, ether, alcohol, &c. The vapour, when mixed with oxygen gas, detonates by electricity. For complete combustion, one volume of the vapour requires 7-5 volumes of oxygen gas, and there are formed six volumes of carbonic acid gas: six of the volumes of oxygen gas went to the formation of carbonic acid. The remaining 1∙5 volumes of oxygen united with three volumes of hydrogen gas, and formed water. It is evident from this, that one volume of the vapour is composed of six volumes carbon vapour and threevolumes hydrogen gas condensed into one volume; so that its specific gravity is 2∙7083, and it is a compound of
[table]

and its atomic weight is 4∙875. This compound differs from all the species of carbo-hydrogen, containing twice as many atoms of carbon as of hydrogen. It might be distinguished by the name of bicarbo-hydrogen ; and the peculiar species just described might be called trito-bicarbo-hydrogen.

7. The portion of the oil which boiled at 186°, but remained liquid at zero, differed obviously from the portion which congealed at zero. Its specific gravity at 60° was 0 ’ 86. Its vapour at 60° had a specific gravity of 2∙9166. A volume of this vapour is composed of six volumes carbon vapour and six volumes hydrogen gas condensed into one volume. Hence its specific gravity is 2∙9166, and it is a compound of
[table]

so that its atomic weight is 5 ’ 25. It constitutes a new species of carbo-hydrogen, and must be denominated hexa-carbo-hydrogen .

8. Naphthaline. This is a substance which is obtained during the distillation of coal tar, a semifluid substance, which distils over during the formation of coal gas. It is a white substance in scales, having a pearly lustre. It has an aromatic smell, and a pungent and disagreeable taste. It is very little heavier than water. It melts at 174°, and boils at 410°. It is easily sublimed, and is always deposited in crystalline plates. It does not burn easily, but when suddenly heated it may be made to burn with a strong yellow flame, emitting much smoke. It is very slightly soluble in water, but dissolves readily in alcohol and ether, and in volatile and fixed oils. It dissolves in sulphuric acid, and forms an acid to which the name of theio-naphthalic acid may be given. It is composed of carbon and hydrogen, in the ratio of one and a half atom carbon to one atom hydrogen; but the number of atoms of each constituent that go to the formation of an integrant particle of naphthaline is still unknown. From the analysis of theio-naphthalic acid by Faraday, it is probable that naphthaline is a compound of
[table]

This would make its atomic weight 12∙5, and it might be called deha-sesqui-carbo∙hydrogen, if a name indicating the number and ratio of its atomic constituents were to be considered as proper.

Coal gas, now so extensively used in this country for lighting the streets of our towns, and even in private houses, is obtained by distilling cannel coal in iron or clay retorts, and purifying the gas which is evolved. Its goodness depends not only on the nature of the coal employed in its production, but also upon the heat to which these coals are exposed, the gas being always the better the lower the temperature at which it is evolved. It consists of a mixture of different gases, which have been described in this section. The higher the specific gravity of the gas, the better is it fitted for the purposes of illumination. The specific gravity is sometimes as high as 0∙650, and sometimes as low as 0 , 345. It is usually a mixture of olefiant gas, carburetted hydrogen, carbonic oxide, and hydrogen gases. The following table exhibits the constitution of a portion of coal gas of the specific gravity of 0 ’ 620, analysed by Dr Henry:
[table]

The constituents of an oil gas of the specific gravity 0∙909 were determined by Dr Henry as follows:
[table]

The illuminating power of the best oil gas is to that of the best coal gas as 2∙25 to 1.

VI. Carbon, so far as we know at present, combines with azote in only one proportion, and forms a very important compound, discovered by Gay-Lussac in 1815, and called by him cyanogen.

It may be obtained by exposing prussiate or cyanodide ∖ of mercury^[6. A salt obtained by boiling in water a mixture of prussian blue and red oxide of mercury, and crystallizing the colourless liquid thus obtained. ] to a heat rather under redness. The salt blackens, and a gas is extricated, which must be received over mercury.

It is colourless, has a strong and disagreeable smell. Its specific gravity is 1 ’ 8055. It cannot be breathed without destroying life. It burns with a purple flame. Water absorbs 4ģ-, and alcohol 40 times its volume of this gas. For complete combustion it requires twice its volume of oxygen. The products from the combustion of one volume of cyanogen are two volumes of carbonic acid and one volume of azotic gas. Hence a volume of it is composed of two volumes carbon vapour and one volume azotic gas condensed into one volume. We have from this the specific gravity of the gas,
[table]

and its atomic weight
[table]

Cyanogen has the property of combining with a great variety of bodies, and forming many important compounds, which will occupy our attention in a subsequent part of [7:6:373] this article. It bears a striking analogy to the supporters of combustion, and resembles them in the nature of the compounds into which it enters.

Sect. IV.— Of Boron.

Borax is a salt usually imported from Thibet and China, where it is found on the borders of certain lakes. It exists also (at least one of its constituents) in certain lakes in Tuscany and Sicily, seemingly in large quantities. When this salt is dissolved in hot water, and the solution mixed with sulphuric or nitric acid till it becomes sensibly sour, if we set it aside till it cools, a quantity of fine white sealycrystals are deposited. These constitute boracic acid, one of the constituents of boron, the other constituent being soda. When one part of dry powdered boracic acid is mixed with two parts of potassium in a platinum crucible, and heated to incipient ignition, a detonation takes place, the boracic acid is decomposed, giving out its oxygen to the potassium, while its base, boron, is set at liberty. Mix the matter in the crucible with water, and throw it on a filter. Potash is dissolved in the water, while the boron remains on the filter.

When washed and dried, it is a powder of a deep-brown colour, almost black, and without either taste or smell. In close vessels it may be exposed to the most violent heat that can be raised, without any alteration. It is insoluble in water, alcohol, ether, and oils, whether hot or cold. It does not decompose water. It is a non-conductor of electricity. When heated in air or oxygen it burns with splendour, and is converted into boracic acid. The atomic weight of boracic acid, determined from the composition of borax, is three. There is reason to believe that when boron is converted into boracic acid, it combines with twice its weight of oxygen. Hence the atomic weight of boron must be 1, and boracic acid is a compound of
[table]

Boron combines readily with chlorine, and forms an acid compound which is in the state of a gas. It may be called borοchloric add. It may be obtained by putting a mixture of very dry boracic acid and charcoal into a porcelain tube, heating the mixture to redness, and passing a current of chlorine gas through it. The boracic acid is decomposed by the joint action of the chlorine and charcoal. The gas which is extricated is a mixture of two volumes borochloric acid and three volumes oxide of carbon. Borochloric acid is a colourless gas, possessing the mechanical properties of common air. It has a very strong and peculiar smell. When it comes in contact with common air it gives out thick vapours. Its specific gravity, according to Dumas, is 3∙942. Water absorbs it with avidity, and the gas is changed into muriatic and boracic acids by the decomposition of water. It is absorbed also by water. This gas has not yet been subjected to a satisfactory analysis.

We are not acquainted with any compound of boron with bromine or iodine; but it has the property of combining with fluorine, and of forming a powerful acid, to which the name of fluoboric acid has been given. It was discovered by Gay-Lussac and Thenard, and may be obtained by heating a mixture of one part anhydrous boracic acid, two parts fluor spar, and twelve parts of sulphuric acid. A gas comes over, which must be collected over mercury. A still easier method is to dissolve boracic acid in fluoric acid, and apply a slight heat.

Fluoboric acid is a colourless gas, having a smell similar to that of muriatic acid, and an exceedingly acid taste. Its specific gravity is 2∙3611. Water absorbs 700 times its volume of it, and a liquid is obtained of the specific gravity 1∙77. It has a certain degree of viscosity, and requires a high temperature to cause it to boil. This acid seems to be a compound of
[table]

and its atomic weight is 4∙25.

The combinations of boron with hydrogen, azote, and carbon, are still unknown.

Sect. V.— Of Silicon. Quartz or rock-crystal, which constitutes so large a portion of the crust of the earth, consists essentially of a peculiar acid substance, to which the name of silica or silicic acid has been given. It is a white tasteless powder, insoluble in water, but capable of combining with the different bases in definite proportions, and forming compounds analogous to the salts.

Silica constitutes one of the constituents of fluosilicic acid, a gas which is extricated when a mixture of fluor spar and sulphuric acid is heated in a glass retort. If we mix fluosilicate of potash in powder with five fourths of its weight of potassium, and apply heat, a violent combustion takes place, and a coherent mass of a liver-brown colour is the result. Digest this substance in cold water. A brown matter remains, which must be well washed in cold water, and then dried; it is silicon, or the basis of silica.

Silicon is a powder of a deep-brown colour, and so similar in its appearance to boron, that it would be difficult to distinguish them. It is a non-conductor of electricity. It stains the fingers, and adheres to every thing that comes in contact with it. It may be exposed to a very high temperature in close vessels without fusion, but it becomes harder, and its properties are materially altered.

Before having been strongly heated, it is readily combustible in the air, and burns with a lively flame. By this combustion about one third of it is converted into silica, which forming a crust, prevents the other two thirds from coming in contact with the atmosphere, and consequently from burning. There is always a quantity of water formed at the same time, showing that the silicon before ignition is not pure, but is combined with a certain quantity of hydrogen. It is not acted on by sulphuric or nitric acid, or aqua regia, but liquid muriatic acid dissolves it even without the application of heat. So also does a concentrated solution of caustic potash when assisted by heat.

After silicon has been ignited, its specific gravity is higher than 1∙837. It neither burns in air nor in oxygen gas. It is not altered by the action of the blowpipe, even when mixed with chlorate of potash; nor does it burn though heated to redness with saltpetre. Neither fluoric acid nor solution of caustic potash has any action on it; but a mixture of fluoric and nitric acid dissolves it with great facility, while at the same time deutoxide of azote is given out.

When mixed with dry carbonate of potash or soda, and heated far below redness, it burns vividly at the expense of the carbonic acid; carbonic oxide is disengaged, and the residue is tinged black by carbon deposited. By this process the silicon is converted into silica, which combines with the alkali. The atomic weight of silica is 2. From the phenomena of the combustion of silicon, it follows that silica is composed of equal weights of silicon and oxygen. Hence it follows that the atomic weight of silicon is 1, and that silica is a compound of
[7:6:374]
[table]

When silicon is heated in chlorine gas, it burns vividly, and is rapidly volatilized. The compound thus formed condenses into a colourless liquid, which is a chloride of silicon. It is limpid, and very volatile. It boils below 212°, and the specific gravity of its vapour, as determined by Dumas, is 5∙939. It has a suffocating smell, not unlike that of cyanogen. It seems to possess acid properties. When dropt into water, it swims on the surface of that liquid, and is gradually dissolved, depositing at the same time a little gelatinous silica. By the action of water it is converted into muriatic acid and silica. It follows from this that chloride of silicon is composed of
[table]

Its atomic weight is 5∙5. Now 5∙5 × 1∙1111 ≡≡6∙1111. This must be the true specific gravity of the gas. It is a little higher than the statement of Dumas.

The bromide and iodide of silicon still remain unknown.

Silicon unites with fluorine, and forms an acid gas, first noticed by Scheele, and now known by the name of fiuosi-licicacid. It is formed when a mixture of fluor spar and sulphuric acid is heated in a glass retort. The gas is transparent and colourless, smokes when mixed with moist air, has a smell similar to that of muriatic acid, is rapidly absorbed by water, while at the same time gelatinous silica is deposited in such abundance as speedily to deprive the water of its liquidity. The specific gravity of this gas is 3 , 6. By means of ammonia it may be resolved into fluoric acid and silica; and from the proportions of these obtained, there can be little doubt that the gas is a compound of
[table]

so that the atomic weight of this acid is 3∙25.

The brown matter described at the beginning of this section is obviously a silicet of hydrogen, or a compound of silicon and hydrogen. It has not been analysed, but is probably a compound of
[table]

No compound of silicon and azote has hitherto been obtained; but silicon and carbon combine when they come in contact in a nascent state. This carburet, which is a dark-brown powder, burns when heated, silicic and carbonic acid gas being formed, but without any sensible augmentation of weight.

No compound of silicon and boron has been hitherto obtained.

Sect. VI.— Of Sulphur. Sulplmr, or brimstone as it is also called, has been known from the earliest ages, as it occurs abundantly in the earth, either in a state of purity, or combined with different metals, particularly iron, copper, lead, and antimony.

It is a brittle substance, having a greenish-yellow colour, without any smell, and having a weak though sensible taste. It is a non-conductor of electricity, and has a specific gravity of 2 ’ 0332. It is not altered by exposure to the air, and is insoluble in water, but slightly soluble in alcohol, ether, and oils both fixed and volatile, ∏ ∙∙< <

When heated to 170°, it is volatilized in the state of a fine powder called flowers of sulphur. It melts at 218°, and is very liquid and amber coloured till the temperature reaches 252°. About 340° it begins to get thick, and assumes a reddish colour; and between ,428° and 482° it is so thick that the vessel containing it may. be inverted without spilling a drop. From 482° to,its boiling point, which is not far from 750°, it becomes thinner, but never so thin as when below 248°, and its reddish-brown colour does not alter. When suddenly cooled when in the most liquid state, as by throwing it into water, it becomes hard and brittle; but if it be suddenly cooled when viscid, it remains quite soft,so that it maybe drawn out into threads. In the first case it crystallizes, in the second case it does not.

It crystallizes in two different and incompatible forms. 1. An octahedron with scalene triangular faces. It consists of two four-sided pyramids applied base to base, the common base of which is a rhomboid, the larger diagonal of which is to the shorter as five to four. It is found crystallized in this state native. 2. An oblique prism with a rhombic base. The. larger angle of the base is 90° 32', and the base makes an angle of 85° 54' with the lateral faces of the prism. This is the form which sulphur assumes when it is fused and left to cool slowly.

I. Sulphur combines with five different proportions of oxygen, and forms five compounds, all of which are possessed of acid properties. These are sulphuric acid, sulphurous acid, hyposulphurous acid, subsulphurous acid, and hyposulphuric acid.

1. Sulphurous acid. When sulphur is heated to the temperature of about 300° in the open air, it takes fire and burns with a pale blue flame, and at the same time emits abundance of fumes, having a very suffocating odour. By this combustion it is converted into an invisible gas, to which the name of sulphurous acid has been given. The easiest method of obtaining this gas in a state of purity is to heat a mixture of sulphuric acid and mercury in a small glass retort by means of a spirit-lamp. An effervescence takes place, and a gas is extricated which must be received over mercury.

It is colourless, and possesses the mechanical properties of common air. It has a strong suffocating odour, precisely the same as that of burning sulphur. It converts vegetable blues into red, and gradually destroys them. Its specific gravity is 2∙2222. Water absorbs about thirty times its volume of this gas, and acquires the taste, smell, and properties of sulphurous acid. When sulphur is burnt in oxygen gas, the volume of the gas is not altered; but it is converted into sulphurous acid, while at the same time the sulphur disappears. It is evident from this that sulphurous acid is a compound of oxygen and sulphur, and that it contains its own volume of oxygen gas. But the specific gravity of sulphurous acid is just double that of oxygen gas. It must therefore be composed of equal weights of oxygen and sulphur. Its constituents must be
[table]

Now, by analyzing the sulphites (as the salts consisting of sulphurous acid combined with a base are called), it can be shown that the atomic weight of sulphurous acid is 4, if we represent the atomic weight of oxygen by unity. If we suppose this acid to be a compound of one atom of sulphur and two atoms of oxygep, then the atomic weight of sulphur will be 2.

2. Sulphuric acid. This, acid is made in great quantities< for the use of bleachers and other manufacturers, by burn- ĩ ing sulphur in leaden chambers. At the same time a quantity of nitric acid from thedeċomposition of saltpetre [7:6:375] is let into the chamber. The sulphur is converted into sulphurous acid. Five atoms of this acid unite with one atom of nitric acid and two atoms of water, and form a white solid salt, which falls to the bottom of the chamber into a quantity of water placed to receive it. As soon as it comes in contact with the water a strong effervescence takes place, the nitric acid is decomposed and converts the sulphurous into sulphuric' acid, while at the same time a quantity of deutoxide of azote is disengaged. This gas coming in contact with the oxygen of the air, is converted into nitric acid, which combines with an additional dose of sulphurous acid, and is decomposed as before. Thus the process goes on as long as sulphurous acid and oxygen gas exist in the leaden chamber.

Sulphuric acid thus obtained is a colourless liquid, having some viscidity; and when as much concentrated as possible it has a Specific gravity of 1∙837. A stronger acid may be made by exposing sulphate of iron, previously deprived of its water, to a strong heat. When this acid is heated in a retort, a portion of it is Volatilized in the form of a white, fibrous, tough matter, which smokes violently when in contact with the air, and unites with water with great violence. In this state it constitutes sulphuric acid totally destitute of water.

Sulphuric acid is a very powerful and corrosive acid. It is easy, by the analysis ef the sulphates (as the salts containing sulphuric acid are called), to show that the atomic weight of sulphuric acid is five. If we digest two grains of pure sulphur in dilute nitric acid in a retort, we gradually convert them into sulphuric acid. The weight of the acid thus formed is exactly five. Hence it is a compound of
[table]

This constitution of sulphuric acid is further confirmed by the fact, that when four sulphurous acid is combined with a base, and exposed in solution in water to the air, it is gradually converted into five sulphuric acid. Thus we see that four sulphurous acid and five sulphuric acid contain each the same quantity of sulphur, namely two. Consequently the oxygen in them must be, respectively, two and three.

3. Subsulphurous acid. A solution of pure sulphurous acid in water has the property of dissolving zinc without effervescence. The zinc, when thus dissolved, is converted into an oxide by uniting with an atom of oxygen. It must get this atom from the sulphurous acid, which contains two atoms of oxygen. It is obvióusly 'deprived of half its oxygen, and converted into a hew acid composed of
[table]

Its atomic weight is three, and it may be distinguished by the name of subsulphurous acid. It does not źeem capable of existing in a separate state,‘but it unités readily with bases, and forms a genus of salts, to which the name of sub-sιιlpliites may be given. , τ

4. Hypbsulphnroust acid. ' ,y This acid, or at least the salts containing it,’Was discovered fiy ’ Mr. HerschelU If śulphu-ret of calci urn be dissolved in Water,and the solution left for sb⅜ne time, itbecómes colourless; and when ’ th⅛ l solution is evaĮŴrâted, it yields large crystals having tĥè form of sixsided prismSΛ These ,i cry⅛taR Constitute the hypösiilpldte of lime; the acid may easily be transferred from the lime to Other base’s, ãtìd tliüš other hÿpóśbíphftes may be formed . .A∙if t .·< ' ' . ∙t Uł í i t*∙k .' ∙ ř·.! ∙ . ., fl * ⅛ í i í i ∙ Γ.. ŕ í; √ ì I ì.: . <1 *t ».··.».

at pleasure. But the acid does not seem capable of existing in a separate state. Dr Thomson has shown, by the analysis of hyposulphite of soda, that hyposulphurous acid is a compound of
[table]

Its atomic weight is the same as that of sulphuric acid, though its constitution be quite different.

5. Hyposulphuric acid. This acid was discovered by Gay-Lussac and Welter. It may be obtained by the following process: Pass a current of sulphurous acid gas through gray oxide of manganese suspended in water. A neutral salt is formed, which dissolves in the water. To the filtered solution add barytes water till the whole manganese and sulphuric acid be thrown down. There remains in solution hyposulphate of barytes. Crystallize the salt, redissolve it in water, and throw down the barytes by means of sulphuric acid, taking care not to add the acid in excess. Filter the liquid. It now consists of water holding hyposulphuric acid in solution.

This acid is colourless, and destitute of smell. It may be concentrated till the specific gravity amounts to 1∙347. If we carry the process further, sulphurous acid flies off, and sulphuric acid remains behind. It may in this way be completely resolved into sulphurous and sulphuric acid, in the proportion of four parts of the former to five of the latter. It is therefore composed of an integrant particle of sulphuric acid united to an integrant particle of sulphurous acid. Its constituents therefore are,
[table]

and its atomic weight is 9.

Such are the five compounds of sulphur and oxygen. The following little table exhibits the constitution and atomic weight of these compounds:
[table]

II. Chlorine and sulphur are capable of combining, probably in various proportions, though the different compounds have not yet been accurately distinguished from each other.^[7. Hλ Rose has lately examined the chlorides of sulphur, and was unable to form any other than the dichloride. ] When a current of chlorine gas is passed over flowers of sulphur, the sulphur becomes orange coloured, then moist, and is at last resolved into a brownish-red liquid, which is a cldoride of sulphur. A similar compound may be formed by heating sulphur in a dry glass vessel filled with chlorine gas.

The smell of this chloride is strong and peculiar. Its taste is acid, hot, and bitter. It does not change the colour of dry litmus paper, but if the paper be moist it is rendered red. Its specific gravity is about 1∙7. It dissolves sulphur and phosphorus readily. It is very volatile. When dropt into water it is decomposed, sulphur being evolved. When dropt into nitric acid a violent effervescence is produced, and sulphuric acid formed. A specimen of this chloride, analysed by Davy, was found composed of
[table]
[7:6:376]

Another specimen, analysed by Dr Thomson, was composed of
[table]

The first was a chlorides the second a dichloride. When the dichloride is left to spontaneous evaporation, it deposits octahedral crystals of sulphur.

III. Bromide of sulphur is easily formed by pouring bromine on flowers of sulphur. An oily fluid is formed, having a much deeper red colour than chloride of sulphur. It is very volatile, and its smell is analogous to that of chloride of sulphur. Cold water has but little action on it; but with boiling water it slightly detonates; hydrobromic acid is formed together with sulphuric acid and sulphuretted hydrogen. Chlorine decomposes this bromide; bromine is driven off and chloride of sulphur formed. Hence this bromide seems to be a compound of
[table]

and its atomic weight is 12.

IV. Iodide of sulphur is easily formed by mixing the two ingredients in a glass tube, and heating the mixture till it undergoes fusion. A grayish-black mass is obtained, having a radiated structure like that of sulphuret of antimony. It has not been hitherto formed in definite proportions. The usual compound obtained seems to be a compound of
[table]

It is therefore a diodide of sulphur. No doubt an iodide might likewise be obtained.

V. From an experiment of Davy, it seems probable that fluoride of sulphur may be formed, and that it is a liquid. He mixed sulphur and fluoride of lead, and distilled in a platinum vessel. Sulphuret of lead was formed, and a liquid volatilized. But the properties of this liquid have not been determined.

VI. Sulphur forms with hydrogen an important gaseous compound, distinguished by the names of sulphuretted hydrogen and of hydrosulphuric acid. It may be obtained by melting iron filings and sulphur in a Hessian crucible. Leaving the sulphuret thus formed in contact with water for twenty-four hours, and then pouring over it dilute sulphuric acid, a copious effervescence takes place, and sulphuretted hydrogen is evolved abundantly. We may obtain it also very pure by pouring concentrated muriatic acid on sulphuret of antimony in the state of powder.

This gas is colourless, and possesses the mechanical properties of common air. It has a strong foetid and peculiar smell, approaching somewhat that of rotten eggs. Its taste is sweetish, it does not support combustion, nor can animals breathe it without suffocation. Its specific gravity is 1 , 1805. Its refracting power is 2∙187, that of air being unity. When subjected to a pressure of seventeen atmospheres, it is condensed into a transparent and colourless fluid, having a specific gravity of about 0∙9.

Water absorbs 3∙66 times its volume of this gas. Alcohol absorbs it in still greater quantity. It is soluble also in ether. Water thus impregnated has the smell and taste of the gas, and reddens vegetable blues.

This gas is combustible; it burns with a bluish-red flame, and at the same time deposits a quantity of sulphur. For complete combustion we must mix one volume of this gas with one and a half volume of oxygen gas.

When an electric spark is passed through this mixture it is converted into water and sulphurous acid. From this combustion we see that the constituents are hydrogen and sulphur. The sulphurous acid formed amounts to the same volume as that of the sulphuretted hydrogen gas consumed. It is obvious from this that this gas contains one volume of sulphur vapour and one volume of hydrogen gas united together and condensed into one volume; hence its specific gravity is equal to that of these two bodies added together.
[table]

Its atomic constituents are obviously
[table]

and its atomic weight is 2∙125.

When electric sparks are passed for a long time through this gas, the whole sulphur is deposited and pure hydrogen gas remains, but the gaseous volume is not altered. When sulphur is heated in hydrogen gas it is partially converted into sulphuretted hydrogen, but the volume of gas is not altered.

2. Hydrosulphurous acid. When three volumes of sulphuretted hydrogen gas and two volumes of sulphurous acid gas are mixed together over mercury, they unite together, and are condensed into a solid body, which adheres firmly to the sides of the jar. This compound has received the name of hydrosulphicrous acid.

It has an orange colour, an acid and hot taste, and it leaves a disagreeable impression in the mouth. It does not alter litmus paper when dry, but if it be moist the paper becomes red. Water, alcohol, nitric acid, sulphuric acid, decompose it and disengage sulphur. When agitated in barytes water, no immediate precipitate appears. For fusion, a higher temperature is requisite than the fusing point of sulphur. When it is kept in fusion an effervescence takes place, and pure sulphur remains behind. From the proportions employed in forming it, it is obviously a compound of one volume sulphurous acid and one and a half volume sulphuretted hydrogen, or, substituting atoms for volumes, we have
[table]

so that its atomic weight is 7∙1875, or some multiple of that number.

3. There is another compound of sulphur and hydrogen, which was first observed by Scheele, and to which the name of bisulphuret of hydrogen has been given. To form it, we may fuse carbonate of potash in a covered crucible, with a considerable excess of sulphur. By this process we obtain persulphuret of potassium, composed of five atoms of sulphur and one atom of potassium. A concentrated solution of this sulphuret is to be poured into dilute muriatic acid by little and little, taking care to mix the two liquids well after every addition. A yellow oily looking liquid collects at the bottom of the vessel. It is transparent if the process has been successfully conducted. This liquid cannot be preserved, undergoing spontaneous decomposition even in well-closed vessels. It is a compound of
[table]

No compound of sulphur and azote is at present known.
[7:6:377]

VII. Pisulphuret of carbon. Sulphur combines with carbon, and forms a very remarkable compound, first discovered by Lampadius in 1796, while distilling a mixture of pyrites and charcoal. It maybe obtained by filling an inclined poreclain tube with fragments of charcoal, heating it to redness, and making a current of melted sulphur pass slowly through the ignited charcoal. A liquid passes through the tube, which is condensed at the bottom of a glass jar filled with water. Bisulphuret of carbon,'when first formed, is yellow, but when rectified by distillation at the temperature of 110° it is transparent and colourless like water.

Its taste is acid, pungent, and somewhat aromatic. Its smell is nauseous and fetid, though quite peculiar. Its specific gravity is 1∙272. It boils briskly between 105° and 110°. It does not congeal, though cooled down to — 60°. It is very volatile, and produces much cold during its evaporation. A thermometer, the bulb of which is covered with lint moistened with this liquid, sinks in the exhausted receiver of an air-pump to — 82° in less than two minutes. It takes fire when heated to the temperature at which mercury boils, and burns with a blue flame, giving out the smell of sulphurous acid. When its vapour is mixed with oxygen gas it detonates by electricity. If the oxygen gas amount to six or seven times the bulk of the vapour, the whole is converted into sulphurous acid and carbonic acid.

It is scarcely soluble in water, but dissolves readily in alcohol and ether. When passed through redrhot copper filings, it combines with that metal, forming a carbo-sulphuret. When passed slowly through red-hot peroxide of iron it is completely decomposed, and converted partly into sulphuret of iron, and partly into sulphurous acid and carbonic acid gases. By these processes the proportions of its constituents have been determined, and it has been found a compound of
[table]

consequently its atomie weight is 4∙75.

2. There seems likewise to be a solid compound of sulphur and carbon, but its properties have not been accurately investigated. When gunpowder (which is made by triturating together saltpetre, sulphur, and charcoaD is digested in water, the saltpetre is dissolved out. A black matter remains, consisting of sulphur and charcoal, united so intimately that the sulphur cannot be separated by sublimation. But the properties of this substance, which seems to be a compound of five atoms charcoal and one atom sulphur, have not been examined.

3. From an experiment of Scheele, not attended to by modern chemists, it would seem that a gaseous compound of sulphur and carbon also exists. He mixed per-sulphuret of potassium and well-burnt charcoal, and heated the mixture. A gas was obtained having the smell of sulphuretted hydrogen, but not absorbable by water. It was inflammable, and when burnt, the products were carbonic acid gas and sulphurous acid. Chlorine decomposes it instantly, and a portion of sulphur is deposited.

VIII. Sulphurei of boron. When boron is heated to whiteness in the vapour of sulphur, it burns with a red flame. The sulphuret formed is white and opaque. If it be kept red-hot till the vapour of sulphur with which it is surrounded be condensed on the colder parts of the apparatus, it dissolves in water with a violent evolution of sulphuretted hydrogen gas, while the water holds boracic acid in solution. Hence it is probably a bisulphuret, composed of
[table]

When the sulphuret of boron is withdrawn from the fire, as soon as the combustion is at an end it dissolves in water with the evolution of sulphuretted hydrogen gas and the formation of boracic acid; but at the same time a portion of sulphur is deposited. It must, therefore, contain more than two atoms of sulphur combined with an atom of boron.

IX. Sulphuret of silicon. When silicon is heated in the vapour of sulphur, it burns with a red-coloured flame. The product is a w hite-coloured earthy looking matter, which may be preserved unaltered in a dry atmosphere. In a red heat it is slowly decomposed, sulphurous acid being given out and silica remaining. The same decomposition takes place in a moist atmosphere. When thrown into water it is completely resolved into sulphuretted hydrogen and silica, showing that it is a compound of
[table]

Sect. VII.— Of Selenium.

This substance was discovered by Berzelius in a reddish-brown matter, which remained after the combustion of an impure sulphur extracted from the iron pyrites at Fahlun, to supply a small sulphuric acid work in that place. From this matter it may be extracted in the following manner: Put a pound of it into a tubulated retort, and pour over it, by small quantities at a time, a mixture of 8 lbs. muriatic acid of the specific gravity 1∙2, and 4 lbs. nitric acid of the specific gravity 1∙5. To the retort is to be luted a large globular receiver, from which proceeds a glass tube plunging into a flask filled with water. After every addition of acid a violent efferveseence takes place, and abundance of red vapours pass, which give a reddish-yellow colour to the water in the flask. After adding the whole acid, distil it over into the receiver by a gentle heat. Pour the liquid of the receiver back into the retort, and distil again. Add 1⅜ lb. of strong nitric acid to the matter in the retort, and distil it off. Finally, boil the residue in the retort with a sufficient quantity of distilled water, and throw the whole on a filter. To the liquid thus obtained add fresh sulphite of ammonia. The selenium precipitates in large red flakes, which is to be washed and dried. When the liquid is concentrated, the addition of sulphite of ammonia throws down a new dose of selenium. The acid liquor distilled over contains also some selenium, which may be precipitated by putting into it bars of zinc.

Selenium thus obtained, when exposed to a heat rather higher than 212°, melts, and on cooling becomes solid. In this state it has the metallic lustre, and a deep brown colour. Its powder is deep red. It crystallizes with difficulty in cubes, or four-sided prisms. Its specific gravity is 4∙3. It is soft, and easily reduced to powder. Ar 212° it becomes semiliquid, and it melts when raised a few degrees higher. After cooling, it remains long in a soft and semifluid state. It is a bad conductor of heat, and a nonconductor of electricity.

I. It combines with three different portions of oxygen, and forms three compounds, which have been distinguished by the name of oxide of selenium, selenious acid, and selenic acid.

1. Oxide of selenium has not yet been obtained in a separate state. It is formed whenever selenium is strongly heated in the open air, and is distinguished by a very strong smell of horse-radish. Berzelius considers it as a [7:6:378] gas. It does not appear to possess acid or alkaline properties.

2. Selenious acid may be formed by burning selenium in oxygen gas, or by heating it in contact with nitric acid or aqua regia. When the solution cools, the selenious acid is deposited in large prismatic crystals, longitudinally striated, and similar to nitrate of potash. It distils over at a heat inferior to what is necessary to draw over sulphuric acid. It condenses in the receiver in long foursided needles. Its vapour resembles chlorine gas in colour. Its taste is acid, and it leaves a slightly burning impression upon the tongue. It is very soluble in water and alcohol.

The atomic weight of this acid is seven, and it is a compound of
[table]

Hence it is probable that the atom of selenium weighs five, and that selenious acid is a compound of one atom selenium and two atoms oxygen.

3. Selenic acid may be obtained by detonating an intimate mixture of one part of selenium and three parts of nitre, in small quantities at a time, in a red-hot crucible. The residue, which contains seleniate of potash, is to be dissolved in water, and nitrate of lead added to the neutralized solution, till all the selenic acid is thrown down in the state of seleniate of lead. This powder being washed and diffused in water, a current of sulphuretted hydrogen is passed through the liquid, till the whole lead is converted into sulphurct. The filtered liquid, after being heated to drive off' any excess of sulphuretted hydrogen, is an aqueous solution of selenic acid.

It may be concentrated by evaporation, till the temperature reaches 536°. But if we raise the heat higher, oxygen gas is given out, and the acid is changed into selenious. It resembles sulphuric acid in its consistence, and in the heat evolved, when it is mixed with water. In its most concentrated state it consists of
[table]

From the analysis of Mitcherhch, the discoverer of this acid, it is a compound of
[table]

We perceive that concentrated selenic acid is a compound of
[table]

The compounds of selenium and oxygen bear a striking analogy to three of the compounds of sulphur and oxygen; namely, subsulphurous acid, sulphurous acid, and sulphuric acid. This will be evident from the following table.
[table]

Whether substances analogous to the other two compounds of sulphur and oxygen may be also formed with selenium and oxygen, remains still to be ascertained.

II. Chlorine and selenium appear to combine in two proportions, forming a chloride and bichloride, the former of which is liquid and the latter solid.

When selenium is put into a glass tube, and a current of chlorine gas passed over it, the selenium absorbs the chlorine, and fuses into a brown liquid. By degrees this liquid, by a further absorption of chlorine, is converted into a solid matter having a white colour. When this matter is heated, it sublimes without melting, and condenses into small crystals in the upper part of the vessel. If any confidence can be put in an imperfect analysis of this substance by Berzelius, it is a compound of
[table]

When selenium is added to this bichloride, a combination may be produced by the assistance of heat, and a deep yellow translucid liquid is obtained, which may be distilled over, though it is much less volatile than the bichloride. It falls to the bottom of water, and is gradually decomposed into muriatic and selenious acids, leaving a quantity of undissolved selenium. According to Berzelius, this liquid is composed of one volume chlorine gas and one volume vapour of selenium, condensed into a liquid. If so, it is composed of
[table]

III. Bromide of selenium may be obtained by simply pouring bromine upon selenium in powder. The two bodies combine rapidly, much heat is evolved, and the bromide formed is solid. It has a reddish-brown colour, gives out vapours, and has the smell of chloride of sulphur. Water dissolves it, converting it into selenious acid and hydrobromic acid. Hence its constituents must be
[table]

Nothing is yet known respecting the combinations of selenium with iodine or fluorine.

IV. But it combines with hydrogen, and forms a gaseous substance, which has been distinguished by the name of selenietted hydrogen gas. When selenium and potassium are fused together, a compound is formed which dissolves in water without the evolution of any gas. The liquid has the colour of beer, and contains in solution hydrosele-niet of potash. When dilute muriatic acid is poured upon seleniet of potassium in a small retort, an effervescence takes place, and selenietted hydrogen gas is driven off.

This gas is colourless, and possesses the mechanical properties of common air. Its smell has some resemblance to that of sulphuretted hydrogen, but it acts much more powerfully, destroying the sense of smell, and occasioning a copious expectoration. It is more soluble in water than sulphuretted hydrogen. The solution precipitates all the metals from their solutions. The gas reddens vegetable blues, and possesses other acid characters. It is a compound of
[table]

so that its atomic weight is 5T25.

The specific gravity of selenietted hydrogen gas has not yet been determined; but there can hardly exist a [7:6:379] doubt that it is 2*8472, for it is undoubtedly composed of one volume selenium vapour and one volume hydrogen gas united together and condensed into one volume. From the analogy of sulphur, there can be little doubt that the specific gravity of selenium vapour is equal to its atomic weight multiplied by 0*5555. But 5 × 0∙5555 = 2∙7777, which, added to 0*0694 (the specific gravity of hydrogen gas), makes 2*8472 for the specific gravity of selenietted hydrogen gas.

Nothing is known respecting the compounds which selenium may be capable of forming with azote, carbon, boron, and silicon.

V. When sulphuretted hydrogen gas is passed through a solution of selenic acid in water, a sulphuret of seleniuŉi is formed, which renders the liquid muddy and lemonyellow, but does not easily separate. The precipitation is facilitated by the addition of some muriatic acid to the liquid. Sulphuret of selenium has a deep orange colour; it softens at 212°, and becomes liquid at a few degrees higher. At a still higher temperature it boils, and may be distilled over. The portion distilled over is transparent, has a reddish-orange colour, and resembles melted orpiment. It dissolves in the caustic fixed alkalies, and in the sulphohydrates: the solution has a very dark orange colour. This sulphuret is not easily acidified by nitric acid *. nitro-muriatic acid acts more powerfully. From the analysis of Berzelius, it appears to be a compound of
[table]

It is therefore a sesquisulphuret, and its atomic weight is 8.

Sect. VIII.— Of Telluriums

This scarce metal was detected in the mine of Maria-holf, in Transylvania, long since abandoned. ' Its peculiar nature was first determined by Klaproth.

. Tellurium has a silver-white colour, and considerable brilliancy. Its texture is laminated. Its specific gravity is 6*1379. It is very brittle, and may easily be reduced to powder. For fusion it requires a temperature rather -higher than what is necessary to melt lead. It easily boils, and it maybe distilled over in a glass retort.

I. So far as we know, it combines with only one proportion of oxygen, and forms a compound possessing at once acid and alkaline properties. It has been called oxide of tellurium. When tellurium is heated before the blowpipe it burns with a blue flame, emitting a white smoke, which is the oxide. It may be obtained most easily by dissolving tellurium in nitro-muriatic acid, and diluting the solution with a large quantity of water. A white powder falls, which is the oxide of tellurium. It is a white, tasteless powder, insoluble in water, but soluble in acids. When heated it melts into a straw-coloured matter, which when congealed assumes a radiated texture. When made into a paste with oil, and heated in charcoal, it is reduced to the metallic state with great facility. It may be volatilized by heat. From the experiments of Klaproth and Berzelius, it would appear that the atomic weight of tellurium is four, and that the oxide is a compound of
[table]

so that its atomic weight is 5.

II. Tellurium burns spontaneously when introduced into chlorine gas. The chloride of tellurium formed is white and transparent. When heated it rises in vapours, and crystallizes. Water decomposes it into oxide of tellurium and muriatic acid. Hence it is probably a compound of
[table]

The combination of bromine and tellurium has not been examined.

III. Iodine combines readily with tellurium when the two substances are brought into contact. The solution in water has a dark purple colour. It combines readily with potash, and forms a colourless solution, which yields, by evaporation, crystals in small white prisms.

Nothing is known respecting the compounds of tellurium with fluorine and azote.

IV. It combines with hydrogen, and forms a gas to which the name of telluretted hydrogen has been given. It may be formed by mixing together oxide of tellurium, potash, and charcoal, and exposing the mixture to a red heat. It is then put into a retort, diluted sulphuric acid is poured on it, and the beak of the retort is plunged under mercury; the gas comes over. It is transparent and colourless, and has a strong smell, somewhat analogous to that of sulphuretted hydrogen. It burns with a bluish flame, and oxide of tellurium is deposited. It possesses the characters of an acid, and is quite analogous to sulphuretted and selenietted hydrogen. No doubt it is a compound of
[table]

If it be a compound of one volume vapour of tellurium and one volume of hydrogen gas condensed into one volume, its specific gravity will be 2*2916.

Tellurium combines with carbon, and the compound is a black powder which has not been examined.

The other combinations of tellurium are still unknown.

Sect. IX.— Of Phosphorus.

Phosphorus is usually prepared from the earth of bones, which consists chiefly of phosphate of lime. This salt is decomposed by means of sulphuric acid. The liquid, freed from sulphate of lime, is evaporated to dryness. A salt is obtained consistingof phosphoric acid combined with a little lime. This salt is mixed with about one sixth of its weight of charcoal powder, and heated strongly in a stoneware retort, the beak of which is plunged into a receiver containing water. The charcoal decomposes the phosphoric acid, and the phosphorus passes over into the receiver in melted drops.

Phosphorus is an amber-coloured and semitransparent solid. Its specific gravity is 1*748. When heated to 108° it melts; it evaporates at 219°, and boils at 554°. It crystallizes in dodecahedrons. It is slightly soluble in alcohol, ether, and oils. When taken internally it acts as a poison. When exposed to the open air (unless the temperature be very low) it emits a white smoke having the smell of garlic, and appears luminous in the dark, undergoing in fact a slow combustion. At the temperature of 148° it burns with a very large bright flame, giving out much white smoke, being converted into phosphoric acid. An orange coloured residue^[8. This is an oxide of phosphorus, composed of three atoms phosphorus and one atom oxygen." ] is left, which, however, may be gradually dissipated by keeping it in a red heat.

I. Phosphorus combines with oxygen in various proportions, two of which have been long known, and distinguished by the names of phosphorous and phosphoric acid.
[7:6:380]

1. The easiest method of obtaining phosphoric acid is to saturate the impure phosphoric acid (separated from earth of bones by means of sulphuric acid) with ammonia, which throws down a little phosphate of lime. When the filtered liquid is concentrated it deposits large crystals of phosphate of ammonia. These crystals are to be cautiously heated in a platinum crucible. They melt and swell up, giving out water and ammonia. The heat is to be continued till the matter in the crucible is reduced to a state of tranquillity. Let it be now kept for a little in a red heat, in a state of fusion. On cooling, it will be pure phosphoric acid.

Phosphoric acid thus prepared is a transparent solid body like glass; its taste is acid. It dissolves very slowly in water; but when sufficiently digested in it, that liquid dissolves a great deal of the acid, without showing any disposition to deposit it again. Liquid phosphoric acid thus obtained is glutinous. It has no smell, but an exceedingly sour taste; it is not corrosive. When heated to redness it parts with most of its water, but not the whole. At a red heat it smokes, and might be wholly volatilized by continuing the heat in an open crucible.

The atomic weight of phosphoric acid is 4∙5, and it is a compound of
[table]

so that if we reckon the atomic weight of phosphorus 2, the acid will contain two and a half atoms of oxygen,— certainly an unexpected proportion; but it seems to be established by incontrovertible experiments.

Mr Clarke observed, that when phosphate of soda is ex- . posed to a red heat, the nature of the acid is changed. He called the newly modified acid pyrophosphoric acid. Common phosphoric acid throws down oxide of silver of a yellow colour, and the salt is not neutral; but pyrophosphoric acid throws down oxide of silver white, and the salt is neutral. The atomic weight of pyrophosphoric acid is precisely the same as that of phosphoric. Hence its constituents must be the same. But phosphoric acid is a stronger acid than the pyrophosphoric, and decomposes the pyrophosphates.

2. Phosphorous acid was first obtained pure by Davy, by dissolving chloride of phosphorus in water, and evaporating the solution. The phosphorous acid was obtained in crystals. This acid has an acid taste, and reddens vegetable blues. It is obviously a very feeble acid. When exposed to the air it absorbs oxygen, and is converted into phosphoric acid; but the change goes on very slowly if the acid be concentrated. When mixed with oxide of mercury it is instantly converted into phosphoric acid, while the oxide assumes the metallic state. If we attempt to dissolve iron or zinc in this acid, sesquihydret of phosphorus is given out, and phosphoric acid remains to unite with the oxides of the metals employed. This acid is a compound of
[table]

so that its atomic weight is 3∙5, and it contains an atom of oxygen less than phosphoric acid.

3. There is another acid of phosphorus which was discovered by Dulong, and to which he gave the name of hypophosphorous acid. It may be obtained thus: Mix together a quantity of barytes and phosphorus, and boil the mixture in a flask with water. Phosphuretted hydrogen gas is given out, and hypophosphite of barytes formed in the liquid. When the process is terminated, the liquid is filtered and mixed with an excess of sulphuric acid, to throw down the barytes. The filtered liquid is left in contact with carbonate of lead. The sulphate of lead remains insoluble, but the hyposulphite of lead dissolves. Filter the liquor and pass a current of sulphuretted hydrogen through it. The lead is thrown down, and hypophosphorous acid remains in solution in the water. This acid has a sharp and very sour taste. It is distinguished by the great solubility of all the salts which it forms in water, every one of them hitherto examined being soluble. According to the analysis of Rose, it is a compound of
[table]

so that it is similar in its constitution to the hyposulphurous acid of Herschel!.

4. When phosphorus is exposed to the air, arranged in the inside of a funnel with a capillary beak, it gradually: absorbs oxygen from the atmosphere, and a liquid drops from the beak of the funnel, which may be received in a proper vessel. This acid was first accurately examined by Dulong, who gave it the name of phosphatic acid By determining the quantity of oxygen absorbed during the formation of this acid, it has been ascertained that it is composed of phosphorus 2, and oxygen 2∙166.

Now we obtain the same ratios if we consider phosphatic acid not to be a peculiar acid, but a compound of
[table]

Now, 2 atoms phosphorus = 6, and 6 ’ 5 atoms oxygen = 6∙5. Dividing by 3, we get phosphorus 2, oxygen 2*166, which is the very constitution found .by experiment.

There is no reason, therefore, to consider phosphatic acid as any thing else than a combination of
[table]

This would make its atomic weight 8. It does not combine with bases and form salts.

II. Phosphorus unites in two proportions with chlorine, and forms two compounds, which have received the name of sesquichloride and perchloride of phosphorus.

1. Sesquichloride of phosphorus may be prepared in this way: Into a tube shut at one end put a quantity of phosphorus, and fill a considerable portion of the tube with corrosive sublimate, and let the extremity of the tube pass into a proper receiver. Heat the portion of the tube containing the corrosive sublimate, then sublime the phosphorus through it. A liquid collects in the receiver, which is sesquichloride of phosphorus.

It is colourless like water, smokes strongly when it comes into the atmosphere, and has an acid and very caustic taste. Its specific gravity is 1∙45. It readily dissolves phosphorus, and usually contains a little of it in solution. When dropt into water it is decomposed and converted into muriatic acid and phosphorous acid. From this decomposition it follows that the chloride is a compound of
[table]

Three atoms of water must be decomposed by every two atoms of the chloride. The three atoms of hydrogen go to the formation of muriatic acid, while the three atoms of oxygen go to the formation of phosphorous acid.
[7:6:381]

2. The perchloride of phosphorus may be formed by burning phosphorus in dry chlorine gas in the proportion of one grain of the former to twelve cubic inches of the latter. It is a snow-white substance, exceedingly volatile, rising at a temperature below that of boiling water. Under pressure it may be fused, and then crystallizes in transparent prisms. When thrown into water it acts with great violence, the water is decomposed, and muriatic acid and phosphoric acid are formed. It is obvious from this decomposition that the perchloride is a compound of
[table]

Two atoms of it decompose five atoms of water, the hydrogen of which unites with the chlorine, and the oxygen with the phosphorus. It is therefore analogous to phosphoric acid in its composition.

III. Bromine and phosphorus likewise combine in two proportions, forming a sesquibromide, which is liquid, and a perbromide, which is solid.

When dry phosphorus is dropt into bromine in a glass tube, the action is violent, both heat and light being evolved. Indeed an explosion usually takes place, and the whole is thrown out of the tube. It is best, therefore, to mix the two bodies in minute quantities at a time. Two compounds are formed; a solid body, which sublimes and crystallizes in the upper part of the tube; and a liquid, which remains at the bottom. The solid contains most bromine; for the liquid may by the addition of bromine be converted into the solid.

1. The liquid or sesquibromide does not lose its fluidity when cooled down to 10∙ o 5. It is very volatile, and emits pungent vapours. It is capable of dissolving an excess of phosphorus. When put into water that liquid is decomposed, and hydrobromic acid formed. When the liquid is evaporated to dryness, a slight combustion takes place, and phosphoric acid remains. We see from this that it was phosphorous acid that was formed at first. Hence it is evident that the sesquihromide must be a compound of
[table]

2. The solid bromide has a yellow colour. When slightly heated it melts into a red liquor, which gives out vapours having the same colour. When these vapours are condensed they crystallize in long needles; but when the fused bromide is allowed to cool, it forms rhomboidal crystals. In the open air it gives out dense and pungent vapours. When mixed with water a double decomposition takes place, hydrobromic acid and phosphoric acid being formed, showing that the constituents of this bromide are
[table]

IV. Iodine and phosphorus combine also in two proportions similar to the chlorides and bromides of the same base.

1. When two parts by weight of phosphorus arc mixed with twenty-four parts of iodine in a glass tube, they unite with great rapidity, and the product is a reddish brown solid body, which melts when heated to the temperature of about 84°. Water decomposes this compound, and converts it into hydriodic and phosphorous acids. Hence it is obviously a sesquiodide composed of
[table]

2. When two parts by weight of phosphorus are mixed with forty parts of iodine, the combination takes place, with equal violence, but the iodide is black, and does not melt till heated to 115°. When dissolved in water it is decomposed and converted into hydriodic and phosphoric acids. Hence its constituents must be
[table]

3. We may also combine
[table]

It has an orange colour, and does not melt till heated to 212°. It may be sublimed unaltered. Water decomposes it into hydriodic acid and phosphorous acid, a little red-coloured phosphorus remaining behind.

V. When phosphorus is mixed with fluoride of mercury or fluoride of lead, and the mixture distilled in a platinum vessel, a liquid passes over, which is probably a fluoride of phosphorus. It is a fuming liquid, which may be burnt in oxygen gas. When mixed with water it is decomposed into hydrofluoric acid and phosphorous acid, showing that it must be a compound of
[table]

It is therefore a sesquifluoride.

The compounds of phosphorus with oxygen, chlorine, bromine, iodine, and fluorine, are quite analogous; and, doubtless, when the investigation of them is farther advanced, they will be all equally numerous.

VΓL Phosphorus combines with hydrogen in various proportions, two of which have been particularly examined.

1. Phosphuretted hydrogens the first of these, may be obtained by the following process: Fill a small retort with water acidulated by muriatic acid, and then throw into it phosphuret of lime in lumps. Plunge the beak of the receiver into water recently well boiled to deprive it of air. An effervescence takes place, and phosphuretted hydrogen is disengaged. Half an ounce of phosphuret of lime yields seventy cubic inches of a gas composed of
[table]

When the gas is obtained by boiling phosphorus in contact with caustic potash, it is composed of
[table]

This gas is colourless, and possesses the mechanical properties of common air. Its smell resembles that of garlic, and it has a very bitter taste. Its specific gravity is 1∙7708. When heated with corrosive sublimate it is completely decomposed, and a quantity of muriatic acid gas is formed, equal to three times the volume of the phosphuretted hydrogen gas. But muriatic acid gas contains half its volume of hydrogen gas. Hence, a volume of phosphuretted hydrogen gas contains one and a half volume of hydrogen gas; the rest is phosphorus. To discover the weight of phosphorus contained in a volume of this gas, we have only to subtract 010416 (the specific gravity of one and a half volume of hydrogen gas) from 1∙7708, the specific gravity of phosphuretted hydrogen. The remainder is 1 ’ 6666. Hence the gas is composed of
[7:6:382]
[table]

Thus it appears that the cas is a compound of
[table]

and its atomic weight is 2425.

When this gas comes in contact with air or oxygen gas, it burns spontaneously with considerable splendour. For complete combustion one volume of the gas requires 1*875 volumes of oxygen gas; but a volume of it contains lį volume of hydrogen gas, which will require 0∙75 volume of the oxygen to convert it into water. There remains 1 ’ 125 volume of oxygen to combine with the phosphorus; but 1 ’ 125 is equivalent to 2 1 1 atoms of oxygen. But phosphorous acid being a compound of 1 atom phosphorus + 1 *, atom oxygen, it is clear that 2į atoms of oxygen will convert 1⅛ atom of phosphorus into phosphorous acid.

A volume of vapour of phosphorus is equivalent to an atom, and its specific gravity is 14111. But the weight of phosphorus in a volume of the gas is l∙6666, which is equal to a volume and a half. Thus it appears that a volume of phosphuretted hydrogen gas is composed of 1⅛ volume of hydrogen gas and l-ļ-volume of phosphorous vapour united together and condensed into one volume.

The gas, then, is a compound of
[table]

and its atomic weight, instead of 2425, is 34 875.

A volume of phosphuretted hydrogen gas will burn also with 2 , 625 volumes of oxygen gas, and be converted into water and phosphoric acid. 0 ’ 75 of the oxygen will go to the formation of water. The remaining 1 - 875 of oxygen will convert the lį volume of phosphorus into phosphoric acid.

This gas may be detonated also with protoxide and deutoxide of azote. When mixed with chlorine gas it burns with a greenish-yellow flame. When the two gases are mixed in the proportion of one volume phosphuretted hydrogen and three volumes chlorine, the whole disappears, being converted into muriatic acid and a brown matter which speedily dissolves in water.

Water absorbs about two per cent, of this gas, and acquires an intensely bitter taste, and a smell similar to that of the gas. It precipitates silver, mercury, and copper, from their solutions of a dark colour. It unites readily to hydriodic acid, and forms a white substance, which crystallizes in cubes. It is composed of one volume of hydriodic acid and half a volume of phosphuretted hydrogen gas.

2. Hydro-phosphoric gas, or sesquihydret of phosphorus, : was first particularly examined by Davy in 1812. He obtained it by heating crystallized phosphorous acid. It may be obtained also by exposing phosphuretted hydrogen gas to the direct rays of the sun. A quantity of phosphorus is deposited, and the gas is changed into sesquihydret.

This gas is colourless, and possesses the mechanical properties of common air. Its smell is similar to that of phosphuretted hydrogen, but not so strong. When mixed with oxygen gas, it does not burn spontaneously unless it be rarefied. When so rarefied as to support a column of mercury twenty inches in height, it detonates spontaneously at 68°; but if the temperature be lower the rarefaction must be carried farther.

Its specific gravity is 1*21527. For complete combustion a volume of it requires one and a half or two volumes of oxygen gas. The products are water and phosphorous or phosphoric acid, according to the quantity of oxygen consumed. When a volume of this gas is heated with corrosive sublimate, it is decomposed, and leaves three volumes of muriatic acid. Hence a volume of it contains one and a half volume of hydrogen gas. The rest is phosphorus.
[table]

Hence the constituents of the aas by weight are,
[table]

But 04875 is l∣- atom of hydrogen, and 2 is 1 atom of phosphorus. Hence the gas is composed of
[table]

and its atomic weight is 24875. It differs from phospĥu-retted hydrogen merely by containing half an atom of phosphorus less.

When mixed with chlorine gas it burns spontaneously with a white flame. Water absorbs the eighth part of its volume of this gas, so that its absorbability is the same as that of olefiant gas.

No combination of phosphorus and azote has yet been discovered.

VIII. Phosphorus and carbon are capable of combining. The compound frequently remains, when phosphuret of lime, after being allowed to remain in water till phosphuretted hydrogen has ceased to be disengaged, is treated with muriatic acid. It is a powder having a dirty lemonyellow colour, and destitute both of taste and smell. It slowly absorbs moisture from the atmosphere. When heated to redness in a close vessel, phosphorus is driven off, and charcoal remains.

IX. Sulphur and phosphorus combine. Put five parts of sulphur, and seven of phosphorus into a glass tube, and melt them together. Agitate this compound in liquid ammonia, and then set the whole aside for some hours. It becomes light yellow, transparent, and of greater fluidity. When left for some weeks in water, it deposits crystals of sulphur, becomes less fluid, and at 40° congeals into a crystalline mass. In this stato it is sometimes a disulphuret of phosphorus, or a compound of
[table]

sometimes a sesquiphosphuret of sulphur, or a compound of
[table]

And probably the two substances combine in other proportions.

X. Selenium and phosphorus may be melted together in almost any proportion. When phosphorus is saturated with selenium, we obtain a very fusible compound, having a dark brown colour, a good deal of lustre, and a vitreous fracture. When the phosphorus is in excess, the compound is red, and destitute of the metallic lustre.

Sect. X.— Of Arsenic.

Arsenic occurs in commerce in the state of a white heavy body, resembling enamel in appearance, and usually known by the name of white arsenic. It is in fact a combination of arsenic and oxygen. When this matter is [7:6:383] mixed with black flux, ^[9. Black flux is cream of tartar exposed to a red heat in a covered crucible till it ceases to smoke. ] and heated in a glass tube or a crucible, over the top of which another crucible is luted, it is reduced to the metallic state, and sublimes into the upper crucible, where it forms a crust.

• Arsenic in this state has a bluish-white colour, and the metallic lustre. It is soft, and so brittle that it is easily reduced to a fine powder by trituration in a mortar. Its specific gravity is 5 ’ 672. When kept for some time at a red heat in a close vessel, it acquires much greater brilliancy, and its specific gravity becomes as high as 5∙959. Its melting point has not been determined, but it is volatilized when heated to the temperature of 365°. When sublimed slowly it crystallizes in tetrahedrons. When exposed to the air, it soon loses its lustre, and becomes a dirty black on the surface.

I. It combines with oxygen in two proportions, and forms two compounds, both of which possess acid properties; they are distinguished by the names of arsenious and arsenic acids.

1. When arsenic is exposed to a moderate heat in contact with the air, it sublimes in the form of a white powder, and at the same time emits a smell resembling garlic. If the heat be increased, it burns with a pale blue flame. The white matter thus formed is arsenious acid, seldom made artificially by chemists, because it is in this state that arsenic occurs in commerce, being sublimed chiefly from certain ores of cobalt.

Arsenious acid is a white, brittle, compact substance. It has a weak but acrid taste, which at last leaves an impression of sweetness. It is one of the most virulent poisons known. A thousand parts of cold water dissolve only two and a half parts of this acid, but 1000 parts of boiling water dissolve 77^ parts of it. The solution has very little taste, but reddens vegetable blues. When slowly evaporated, the acid crystallizes in regular octahedrons. It has been ascertained by accurate experiments that this acid is composed of
[table]

so that its atomic weight is 6∙25, and the atom of arsenic weighs 4∙75. Thus arsenious acid and phosphorous acid are precisely similar in their constitution.

2. Arsenic acid, the other compound of arsenic and oxygen, was discovered by Scheele. It may be obtained by dissolving metallic arsenic in nitric acid, and evaporating the solution to dryness; or by mixing in a retort two parts of muriatic acid of the specific gravity 1∙2, eight parts of arsenious acid, and twenty-four parts of nitric acid of the specific gravity l∙25. The arsenious acid, by the assistance of heat, dissolves with effervescence. Evaporate the solution to dryness; what remains is arsenic acid.

Arsenic acid thus prepared is a white matter, having a weak but acid taste. After exposure to a red heat, it dissolves very slowly in water. However, by long digestion, a very concentrated solution may be obtained, which has an intensely acid taste, and which remains liquid even when evaporated to the consistence of a jelly. The constituents of this acid are,
[table]

so that its atomic weight is 7∙25. It is quite similar in its constitution to phosphoric acid.

II. Arsenic combines with chlorine, and forms a com pound, to which the name of chloride of arsenic has been given. It was formerly called butter of arsenic. It is formed when arsenic is introduced into dry chlorine gas. The metal takes fire spontaneously, and is converted into chloride. But the easiest mode of obtaining it is to mix together six parts of corrosive sublimate and one part of arsenic, and distil, with a gentle heat, in a retort. A liquid passes over into the rcceiver, which is chloride of arsenic. The following is also a very easy process for forming this chloride. Put into a tubulated retort a quantity of arsenious acid, with ten times its weight of concentrated sulphuric acid. Then throw in by the tubular mouth fragments of common salt which have been recently fused to expel all moisture. Chloride of arsenic passes slowly into the receiver. The heat must be kept up, and additional portions of common salt gradually added. Little or no muriatic acid is disengaged; but some hydrous chloride of arsenic at last passes over, and swims on the surface of the anhydrous chloride.

Chloride of arsenic is a transparent liquid, of the consistence of oil. It is very volatile. It boils at 270°. Its specific gravity is greater than that of water. When hot, it dissolves phosphorus or sulphur, but lets them fall again on cooling. It likewise dissolves rosin, and combines with olive oil and oil of turpentine. When mixed with water it is decomposed, arsenious acid precipitating. It is a compound of
[table]

It is therefore asesquichloride, and its atomic weight is 11∙5. The specific gravity of the vapour of this chloride is 6 ’ 4888.

No doubt a perchloride of arsenic exists, containing two and a half atoms chlorine, analogous to arsenic acid; but it has not yet been subjected to examination. It is solid and white.

HI. Bromide of arsenic may be formed by putting a quantity of bromine into a tubulated retort, and throwing into it pulverized arsenic till the metal ceases to burn, gently agitating the retort after every addition. When the compound is formed, it may be distilled over into the receiver to get rid of any excess of arsenic that may have been added.

This bromide becomes solid at 68°, and is liquefied when raised a few degrees higher. It boils, and may be distilled over, at 428°. It has a very light yellow colour. On solidifying it crystallizes in prisms. When mixed with water it is immediately decomposed into hydrobromic acid and arsenious acid. Hence its constituents are obviously
[table]

It is therefore a sesquibromide, analogous to arsenious acid; and its atomic weight is 19∙75.

IV. The best way of forming iodide of arsenic is to mix three parts of arsenic in fine powder, ten parts of iodine, and a hundred parts of water, and to digest the mixture till all smell of iodine disappears. The clear liquid is to be poured off, and subjected to evaporation. At a certain degree of concentration, red crystals of iodide of arsenic are deposited. To obtain the iodide pure, we must evaporate the liquid to dryness, and heat the dry residue till it melts. On cooling it has a brick-red colour, and a crystalline texture. It has no smell. Jt may be sublimed. It dissolves in a large quantity of water; but when mixed with a small [7:6:384] quantity it undergoes decomposition, being converted into hydriodic acid and arsenious acid.

Hence it is a compound of
[table]

It is therefore a sesquiodide.

V. When a mixture of fluor spar, arsenious acid, and sulphuric acid, is heated in a platinum or leaden retort, a fuming colourless liquid passes over, which is a fluoride of arsenic. It smokes, and has a specific gravity of 2∙73. When it comes in contact with water it is converted into fluoric acid and arsenious acid. Hence it must be a compound of
[table]

It is therefore a sesquifluoride, analogous to the other compounds of arsenic, with the simple supporters.

VI. Arsenic combines with hydrogen, and forms a compound which has been called arsenietted hydrogen gas. It maybe obtained by dissolving in muriatic acid an alloy of arsenic and tin, or an alloy of arsenic and zinc, or by heating arsenic in an alkaline ley. By whatever process it is obtained it is always impure, .being mixed with a large proportion of hydrogen gas. Its purity may be determined by exposing it to the action of a saturated solution of sulphate of copper. The arsenietted hydrogen is absorbed, while the pure hydrogen gas remains. Dumas found that a hundred volumes of the purest gas which he could procure was a mixture of from thirty to twenty-eight arsenietted hydrogen, and from seventy to seventy-two hydrogen gas. Arsenietted hydrogen gas is colourless, has a nauseous smell, is not sensibly absorbed by water, extinguishes flame, and destroys life. It burns with a blue flame, and if the neck of the vessel containing it be narrow, the arsenic is deposited. It explodes with oxygen gas, water and arsenious acid being formed. Sulphuretted hydrogen occasions no change in it; but if chlorine gas be added to the mixture, the bulk diminishes, and yellow-coloured flakes are deposited. Thus these two gases furnish a delicate test of the presence of arsenietted hydrogen gas. Concentrated nitric acid, when suddenly mixed with this gas, causes an evolution of red fumes, and an explosion accompanied with flame.

When tin is melted in this gas the arsenic is absorbed and the hydrogen set at liberty. A volume of the gas, after this treatment, leaves one and a half volume of hydrogen gas. For complete combustion, one volume of the gas requires one and a half volume of oxygen gas. Of this 0∙75 volume went to the formation of water. There remains 0∙75 (equivalent to one and a half atom) to combine with the arsenic, indicating a volume of arsenic vapour, equivalent to one atom of arsenic. Hence the gas is a compound of
[table]

Hence the atomic weight must be 4∙9375. The weight of a volume of arsenic vapour deduced from the atomic weight of arsenic is 2∙6888. Consequently the specific gravity of the gas must be 2∙79305.

Nothing is known respecting the combinations of arsenic with azote, carbon, boron, or silicon.

VII. Sulphur and arsenic combine in various proportions. Four of these compounds are known, and have been subjected to analysis.

1. Sulphuret, or realgar. When a mixture of sulphur and arsenic is melted in a covered crucible, a red vitreous mass is obtained, which is sulphuret of arsenic. It may be obtained also by heating arsenious acid and sulphur. It is found native, and is then usually distinguished by the name of realgar. It has a scarlet colour, and is frequently crystallized in prisms. Its specific gravity is 3∙3384. It is tasteless, and slightly poisonous. It is sometimes used as a paint. It is composed of
[table]

and its atomic weight is 6∙7u.

2. Sesquisulphuret, or orpiment. If arsenious acid be dissolved in muriatic acid, and a solution of sulphuretted hydrogen in water be poured into the liquid, a fine yellowcoloured powder falls to the bottom. This powder is usually called orpiment. It may be formed by subliming arsenic and sulphur by a heat not sufficient to melt them. This substance is found native. It is composed of thin plates, which have a considerable degree of flexibility. Its specific gravity is 3∙4522. It is composed of
[table]

Its atomic weight is 7∙75.

3. Sulphide. WTιen a current of sulphuretted hydrogen gas is passed through a moderately concentrated solution of arsenic acid in water, a yellow-coloured precipitate falls, very much resembling orpiment in its appearance. It is much less fusible than sulphur, and when fused its colour becomes reddish. It sublimes unaltered, and forms a reddish-brown mass, not the least crystalline. When it is boiled in alcohol, a little sulphur dissolves and crystallizes as the alcohol cools. The alkaline hydrates and concentrated ammonia dissolve it. It decomposes the sulphohydrates and the carbonates. Its constituents are
[table]

It is therefore analogous to arsenic acid in its constitution.

4. Persulphuret of arsenic. It may be obtained by precipitating a neutral solution of sulpharseniate of potash, or soda, by means of alcohol, filtering the solution, and distilling off the half or two thirds of the alcohol. When the residual liquid is allowed to cool, it deposits groups of yellow brilliant crystals, very bulky and light. These crystals are composed of
[table]

VIII. Arsenic combines readily with phosphorus. The phosphuret may be formed by distilling equal parts of arsenic and phosphorus over a moderate fire. It is black and brilliant, and should be kept under water.

IX. Selenium, when in fusion, dissolves arsenic by degrees. The excess of either body sublimes if the heat be continued, and we obtain a seleniet in the form of a black and very fusible mass. It has a vitreous fracture.

Sect. XI.— Of Antimony.

Antimony exists in the earth most commonly in the state of sulphuret. The metal, as it occurs in commerce, is never quite pure; but it may be purified thus: Reduce it to a fine powder, and mix it with its own weight of antimonic acid, and fuse it in a crucible. The impurities[7:6:385] are all oxydized by the oxygen of the acid, and the metal remains pure.

Pure antimony has a silver-white colour. Its texture is fibrous, but it does not present the broad plates of the antimony of commerce. It crystallizes in octahedrons. It is easily reduced to a fine powder by pounding in a mortar. Its specific gravity is 6 ’ 4366. It melts at 810°, or just at incipient redness. When heated to whiteness before the blowpipe, and thrown on the table, it burns with great splendour, giving out a white smoke, and rolling on the table. It undergoes no change by exposure to the air, except a diminution of its lustre. At a red heat it decomposes water, and is oxydized.

I. Antimony combines with oxygen in three proportions, and forms three compounds, two of which possess acid properties. The other is an oxide, which constitutes the base of all the active medicinal preparations of this metal.

1. Oxide of antimony may be obtained thus :—Dissolve antimony in muriatic acid, and dilute the solution with water. A white curdy precipitate falls. Wash it with water, and boil it for some time in a solution of carbonate of potash. Then wash it well, and dry it on a filter.

It has usually a dirty-white colour. When obtained by sublimation, when it is known by the name of argentine flowers of antimony, it has a white colour and a silky lustre. When heated it assumes a yellow colour. When heated to redness in the open air it glows like tinder, and is converted into arsenious acid. In a retort it may be fused and distilled over at a red heat, if air be excluded.

Glass of antimony is this oxide combined with some sulphuret of antimony. Liver of antimony is the same compound with a greater proportion of sulphuret, which renders it opaque, and of a liver colour.

This oxide is a compound of
[table]

on the supposition that the atomic weight of antimony is eight. So that oxide of antimony is analogous in its composition to phosphorous and arsenious acids.

2. Antimonious acid is easily obtained by oxydizing antimony by means of nitric acid, evaporating to dryness, and exposing the residual matter to a red heat. It has a snow-white colour, but becomes yellow when heated. It cannot be fused nor sublimed at a red heat; nor is it so easily reduced to the metallic state when heated with charcoal, as protoxide of antimony. When heated with a mixture of charcoal and potash, it may be obtained in the metallic state. It combines with bases, and forms sajts, to which the name of antimonites has been given. Antimonious acid is a compound of
[table]

so that its atomic weight is 10.

: 3. Antimonic acid may be obtained by dissolving anti mony in aqua regia, evaporating the solution to dryness, adding nitric acid to the residue, and heating it till that acid is expelled. - We must beware of raising the temperature to redness, otherwise the antimonic acid will lose oxygen, and be converted into antimonious acid.

It is a straw-coloured powder, tasteless, and insoluble in water. When heated with alkaline carbonates in a crucible, the carbonic acid is driven off, and antimoniates formed. It dissolves in boiling caustic potash. The acids precipitate from this solution hydrated antimonic acid in the state of a white powder. Antimonic acid is composed of
[table]

so that it is analogous to phosphoric and arsenic acids.

II. So far as we know at present, chlorine and antimony combine only in two proportions, and form two chlorides analogous to oxide of antimony and antimonic acid.

1. When two parts of corrosive sublimate and one part of antimony are mixed together and distilled, a fatty mass of a grayish-white colour comes over, often crystallized in four-sided prisms. It was formerly called butter of antimony. It melts at a moderate heat, is very volatile, and is decomposed when mixed with water into muriatic acid and protoxide of antimony, without any trace of antimonious or antimonic acid. It is therefore a sesquichloride composed of
[table]

2. Perchloride of antimony may be formed by passing a current of chlorine gas over heated metallic antimony. The metal burns vividly, emitting sparks, while at the same time a volatile liquid is formed, which is the perchloride. It is white, or has only a light-yellowish tinge. It has a strong and disagreeable smell, and fumes in the atmosphere. Exposed to the air it attracts moisture, and is converted into a white mass, in which crystals form; these crystals afterwards dissolve without rendering the solution milky. When mixed with water it is decomposed and converted into antimonic acid and muriatic acid. Hence it must be a compound of
[table]

Thus it is analogous in its composition to antimonic acid.

III. Sesquibromide of antimony may be obtained by putting some bromine into a tubulated retort, and throwing on it antimony in powder as long as that metal continues to take fire. It is then to be distilled over into the receiver. It is much less fusible and volatile than the sesquibromide of arsenic. It melts at about the temperature of 200°, and boils at 518°. It is colourless, and crystallizes in needles. It attracts moisture from the atmosphere. When mixed with water it is decomposed into oxide of antimony and hydrobromic acid. Hence its constituents must be
[table]

IV. Sesquiodide of antimony is easily formed by heating the two constituents together. Any excess of iodine is easily driven off by heat. It is a dark-red solid, which melts readily when heated, and which, when put into water, is converted into oxide of antimony and hydriodic acid. Hence its constituents must be
[table]

V. Fluoride of antimony is a snow-white solid, more volatile than sulphuric acid, but less so than water. It is composed of
[7:6:386]
[table]

It is therefore a sesquifluoride.

No compound of antimony with hydrogen, azote, carbon, boron, or silicon, is known.

VI. Sulphur and antimony combine in three proportions, and form three sulphurets, analogous in constitution to the oxides of antimony.

1. Sesqnisulphuret of antimony is found native, and is met with in commerce in the shape of cones, under the name of crude antimony. It has a bluish-gray colour, and the metallic lustre; a foliated texture, and a specific gravity of 4 ’ 62. It is more fusible than antimony, boils in a high temperature, and may be distilled over without decomposition if air be excluded. It dissolves in muriatic acid when assisted by heat, and is converted into oxide of antimony and sulphuretted hydrogen gas. Hence it is obviously a compound of
[table]

Its powder, when pure, has a reddish-brown colour. It possesses acid properties, and is therefore a sulphide. What is called hermes mineral is merely this sesquisulphide in a hydrous state, and mixed with a very small quantity of antimonite of potash.

2. Bisulphide of antimony is formed when a current of sulphuretted hydrogen gas is passed through a solution of antimonious acid or antimonite of potash. Its colour is orange red. When heated, it gives off sulphur, and is converted into sesquisulphide. It is composed of
[table]

3. Persulphide of antimony may be obtained by passing a current of sulphuretted hydrogen gas through perchloride of antimony, to which tartaric acid has been added to prevent the antimony from precipitating when the liquid is diluted with water, as it must be before the sulphuretted hydrogen gas can be passed through it. It may be easily obtained by fusing together four parts of carbonate of potash, five parts of crude antimony, and one part of sulphur. The fused mass is to be dissolved in boiling water, and precipitated by dilute sulphuric acid. It has a paler colour than bisulphide of antimony, and the colour does not change on drying. It is composed of
[table]

4. Sesqnisulphide of antimony has the property of combining with oxide of antimony, and of forming a compound which occurs native, and is usually called red antimony by mineralogists. Its colour is cherry red. It crystallizes in right square prisms, and has a specific gravity of 4∙5. It is feebly translucent, and sometimes has an adamantine lustre. Its constituents are,
[table]

The sesquisulphide of antimony combines also with iodine.

VII. Selenium and antimony combine readily with the production of heat and light. The compound melts and forms a metallic button, which has a crystalline texture.

VIII. When equal parts of antimony and phosphoric glass are mixed together with a little charcoal powder, and melted in a crucible, phosphuret of antimony is formed. It is white, brittle, and laminated in its texture. When melted, it emits a green flame, and oxide of antimony sublimes.

IX. Antimony forms with arsenic an alloy, which is brittle, hard, and very fusible. The affinity between these two metals is very weak.

Sect. XII.— Of Chromium.

The most common mineral from which this metal is obtained is chromiron ore, imported abundantly into this country from the bare hills near Baltimore, and employed in the manufacture of bichromate of potash, which is employed by the calico-printers as a yellow dye. When oxalic acid is mixed with a solution of this salt in water, and the mixture is digested on the sand bath, an effervescence takes place, and the whole assumes a green colour, the chromic acid being converted into oxide of chromium. The addition of ammonia throws down the green oxide, which being washed and dried, and exposed to a violent heat in a charcoal crucible, is converted into metallic chromium.

It is white, intermediate between the colour of tin and I steel. Its specific gravity, as determined by Richter, is 5∙9. It is very brittle, and easily reduced to powder. It is not acted on by the magnet. It requires a heat to melt it, so high that we can obtain it only in small grains. It conducts electricity. No acid dissolves it readily except the fluoric. When heated with potash, soda, or their carbonates or nitrates, it is easily converted into chromic acid.

I. Chromium combines with two proportions of oxygen, and forms two compounds, which have received the names of green oxide and chromic acid.

1. Green oxide is easily obtained by digesting a mix∙< ture of chromate of potash and oxalic acid till it becomes’ green, and then throwing down the oxide by means of ammonia. If it be dried without the application of heat, it is a light-coloured greenish-blue powder, tasteless, very light, and easily soluble in acids. When dried on a filter at a temperature not so high as 212°, it is much darker, but still retains nearly half its weight of water. A moderate heat expels the water, and leaves the oxide in the state of a beautiful green powder. When heated nearly to redness, it suddenly glows, or becomes red hot like burning tinder. After this it is no longer soluble in acids; yet we may obtain a solution by digesting it for a long time in sulphuric acid. The atomic weight of this oxide is 5. It is a compound of
[table]

It combines with acids, and forms salts, which have a sweet taste, and a green or blue colour, and none of them seems capable of crystallizing.

2. It is only lately that a method of obtaining pure chromic acid has been discovered. It is at follows: Mix together four parts of chromate of lead, three parts of pure fluor spar (previously ignited and pounded), and five parts of sulphuric acid as concentrated as possible. Put this mixture into a leaden or platinum retort, and apply a gentle heat by means of a lamp. A red gas is formed, which appears in the air under the form of red or yellow vapours. When this gas comes in contact with water, it is absorbed and converted into fluoric and chromic acids. By evaporating the solution in a platinum basin, the fluoric acid is driven off, and pure chromic acid remains. It may be obtained in regular four-sided prisms by a very cautious evaporation of its solution in water.
[7:6:387]

Chromic acid, when dry, is almost black while hot, and of a deep red while cold. It has no smell. Its taste is intensely sour, leaving a styptic impression behind. It stains the skin yellow. It is soluble in alcohol, and the solution is partially decomposed by heat, ether being evolved, and green oxide precipitated. The atomic weight of this acid is 6∙5, and it is composed of
[table]

It is therefore analogous to phosphoric, arsenic, and antimonic acids in its composition.

II. Chlorine and chromium probably unite in various proportions, few of which, however, have been accurately examined.

1. Muriatic acid readily dissolves green oxide. The solution has a deep-green colour, a sweet taste, and always contains an excess of acid. When evaporated to dryness it assumes the form of red-coloured scales, which constitute a chloride of chromium. They readily dissolve in water, with a deep-green colour and a sweet taste. When the heat is raised sufficiently high to drive off all excess of acid, the chloride becomes tasteless, and refuses to dissolve in water or acids.

2. There is another compound of chlorine and chromic acid, discovered by Dr Thomson in 1824, and called by him chlorochromic acid. It may be thus obtained. Triturate together in a mortar 190 grains of dry bichromate of potash and 225 grains of. decrepitated common salt, and pour upon the mixture 500 grains of concentrated sulphuric acid, and take care to mix it with the powder into a magma. Apply the heat of a lamp to this mixture, previously put into a small retort. An effervescence takes place, and beautiful red fumes make their appearance. These condense in the beak of the retort, and drop into the receiver in the form of a red-coloured liquid, which has a sweetish, astringent, and acid taste. It has an exceedingly intense smell of chlorine. It reddens vegetable blues. Its specific gravity is 1*9134. When dropt into water it falls to the bottom, and exhibits the appearance of a drop of oil; globules of chlorine gas are given out copiously till the globule disappears, while at the same time the liquid becomes yellow. When the red liquid is dropt .into oil of turpentine or alcohol, it sets these combustible bodies on fire; and they burn quietly, with a flame having a good deal of blue mixed with white. Sulphur is also set on fire by the liquid. It burns with a fine red flame. It acts very feebly on the metals. This liquid would appear, from the analysis of Dr Thomson, to be a compound of
[table]

The bromides and iodides of chromium are still unknown.

III. The red-coloured gas mentioned in this section is probably a fluoride of chromium. It is permanent at the usual temperature of the atmosphere. When mixed with ammoniacal gas it burns with explosion. It gradually corrodes and dissolves resin.

Nothing is known respecting the compounds which chromium may be capable of forming with hydrogen, azote, carbon, boron, and silicon.

IV. Sulphuret of chromium maybe obtained by various processes; as by passing a current of sulphuretted hydrogen gas over green oxide of chromium, heated to redness in a porcelain tube, or by heating a mixture of equal weights of chloride of chromium and sulphur in a glass tube to as high a degree as the glass will bear. It is a blackish-gray solid body, unctuous to the touch, and fri able. When heated in the open air it burns like pyropho-rus, leaving green oxide of chromium. By digestion in nitric acid, it may be converted into sulphate of chromium. It is clear from this that its constituents are,
[table]

V. When phosphorus is made to pass through green oxide of chromium, heated to redness in a glass tube, a brilliant combustion takes place, and phosphuret of chromium is formed. It is brown, tasteless, and insoluble in water, and still retains a pulverulent form. Its constituents are,
[table]

The compounds of chromium with selenium, tellurium, arsenic, and antimony, are unknown.

Sect. XIII.— Of Vanadium.

Vanadium was discovered during the year 1830, by Μ. Sefström, in a Swedish iron remarkable for its ductility. It is the produce of the iron mine of Taberg, not far from Jönköping. It exists also in an ore of lead, which occurs at Zimapan, in Mexico which was analysed in 1801 by Del Rio, who stated that it contained a new metal, to which he gave the name of erythronium. But Descotils repeated the analysis, and announced that the supposed new metal was chromium. The same ore of lead (vanadiate of lead) occurs in an abandoned lead mine in the county of Wicklow. It has a dirty orange-yellow colour, and is crystallized in tubes.

Sefström extracted vanadium from the scoriae of the iron of Taberg, which he found richer in that metal than the iron itself. His method was as follows: The scoriae are reduced to a fine powder, and mixed with their own weight of nitre, and twice their weight of carbonate of soda. This mixture is strongly heated for an hour. When cold, the mass is pounded and digested in water till every thing soluble is taken up; the solution is neutralized with nitric acid, and mixed with acetate of lead. A yellow precipitate falls, which is vanadiate of lead, but not quite pure. While this precipitate is still moist, it is decomposed by concentrated sulphuric acid. The liquid assumes a dark-red colour. After half an hour’s digestion alcohol is added, and the digestion continued. Ether is formed, and the vanadic acid being reduced to the state of oxide, becomes blue. The blue solution is concentrated to a syrup, and then mixed in a platinum crucible with a little fluoric acid, and heated to get rid of a quantity of silica, which could not be otherwise separated. Then evaporate to dryness, and ignite to drive off the excess of sulphuric acid. What remains is an impure vanadic acid. Fuse it with nitre, added in small quantities at a time, till a small quantity of the mass taken out, and allowed to cool, ceases to become red. Then dissolve the mass in water, and filter. Into the filtered liquor put a piece of sal ammoniac, so large that the whole will not dissolve. A white powder falls, which is vanadiate of ammonia. Let it be washed first in a solution of sal ammoniac, and then in alcohol of the specific gravity 0∙86. Then dissolve it in boiling water, and allow it to crystallize. From this salt, by heating it in an open vessel, we obtain vanadic acid, and by heating it in a close vessel, oxide of vanadium.

To obtain metallic vanadium from vanadic acid, pass a current of chlorine gas through an intimate mixture of vanadic acid and dry charcoal. A liquid and volatile chloride of vanadium is obtained. Put this chloride into [7:6:388] a hollow ball blown in a barometer tube, and pass a current of ammoniacal gas through it till the chloride be completely saturated, which takes place speedily, and with the disengagement of heat. Then apply a spirit-lamp to the hollow ball, while the current of ammoniacal gas still continues to flow. Sal ammoniac is disengaged, and the reduced vanadium remains in the ball.

It is white, and resembles silver, or rather molybdenum, to the appearance of which last metal it comes very near. It is not malleable, and is easily reduced to powder in a mortar. It is a good conductor of electricity, and strongly negative when compared to zinc. Its specific gravity is still unknown. It dissolves easily in nitric acid and aqua regia. The solution has a fine blue colour. Sulphuric, muriatic, and fluoric acids, do not act upon it even at a boiling heat; nor is it oxydized when heated with the alkaline carbonates. When heated rather under redness it takes fire, and burns with a dull flame, and is converted into a black-coloured oxide.

I. Vanadium combines with three different proportions of oxygen, and forms three compounds.

1. Bloch oxide, or protoxide. This oxide may be obtained by passing a current of hydrogen gas through vanadic acid in a state of ignition, or by fusing vanadic acid in a charcoal crucible. This oxide is coherent, has a black colour, and is a conductor of electricity. It does not seem capable of combining either with acids or bases. When heated in the open air it takes fire and burns, leaving a black matter, which has not been fused. Chlorine gas converts it into chloride and vanadic acid. Its constituents, according to the analysis of Berzelius, are,
[table]

2. Binoxide, or blue oxide. To obtain this oxide, the easiest process is to mix 9į-parts of protoxide and 11⅜ of vanadic acid together, and to heat the mixture to whiteness in an atmosphere of carbonic acid gas. This oxide is infusible at the temperature at which glass softens. It is insoluble in water. When in the state of a hydrate it absorbs oxygen rapidly from the air, becoming first brown, and then green. It dissolves slowly but completely in acids. The solution is blue, and the oxide acts the part of a base; but it combines also with bases, and forms a genus of salts, to which the name of vanadites may be given. This oxide is composed of
[table]

3. I "anodic acid may be obtained by exposing vanadiate of ammonia in an open platinum crucible to a temperature approaching to redness, stirring the mass from time to time. The vanadiate is decomposed, and the residue is at first black, but in proportion as it absorbs oxygen from the atmosphere it assumes a reddish-brown colour, which, when the matter is cold, becomes similar to rust of iron. It is destitute of taste and smell. It strongly reddens moist litmus paper. It melts at a red heat, and may be heated tô whiteness without losing oxygen. When fused it crystallizes on cooling; and though the temperature, before congealing, was below redness, it becomes incandescent, and continues so during the whole time that the crystallization is going on. The acid contracts much in becoming solid, and is easily detached from the crucible. The acid, after fusion, is translucent at the edge, and has a yellowish colour. It is very little soluble in water, but remains long suspended. It is easily reduced to the state of binoxide by the action of tartaric, oxalic acids, &c. assisted by a moderate heat. Muriatic acid dissolves it, assuming an orange colour. This acid is a compound of
[table]

II. Chloride of vanadium is easily formed by the process mentioned at the beginning of this section. It is a volatile liquid, which has not been subjected to analysis.

Nothing is known respecting the bromides, iodides, and fluorides of vanadium. Neither have any attempts been made to combine it with hydrogen, azote, carbon, boron, or silicon.

III. T wo combinations of vanadium and sulphur have been ascertained to exist analogous to binoxide and vanadic acid in their constitution.

1. Bisulphide of vanadium. This compound may be formed by passing a current of sulphuretted hydrogen gas over protoxide of vanadium at the temperature of ignition. It is black, becomes compact by pressure, and when burnished does not assume the metallic’ lustre. Heated on platinum foil it burns with a blue flame, leaving a pellicle, which is blue at the circumference and purple internally. It is insoluble both in acids and alkalies. Nitric acid converts it into sulphate of vanadium. It is composed of
[table]

2. Tersulphide of vanadium. This compound may he obtained by dissolving vanadic acid in an alkaline sulphohydrate. Its colour is brown, not nearly so deep as that of the preceding sulphide. It may be dried and preserved without alteration. When heated it gives out sulphur, and is converted into bisulphide. Sulphuric and muriatic acids do not decompose it. Its constituents are,
[table]

IV. When phosphate of vanadium is exposed to a white heat in a charcoal crucible, a porous mass is obtained, having a gray colour, somewhat like plumbago. It has not undergone fusion.

The other combinations of vanadium are still unknown.

Sect. XIV.— Of Uranium.

This metal is obtained chiefly from pitchblende, a black heavy mineral, which occurs at Johan Georganstadt, in Saxony, and in some other places. From this ore it may be procured in the following manner; Reduces the mineral to powder, and digest it in nitric acid till every thing soluble be taken up. Render the liquid as neutral as possible by evaporation, and pass a current of sulphuretted hydrogen gas through it till all precipitation ceases. Heat the liquid after filtration, to drive off all traces of sulphuretted hydrogen. Precipitate by caustic ammonia. Wash the precipitate, and digest it in carbonate of ammonia. A yellow liquid is obtained, which gradually deposits fine crystals of ammonia-carbonate of uranium. When this salt is ignited, the ammonia and carbonic acid are driven off, and the uranium reduced to the state of protoxide. When a current of hydrogen gas is passed Over this oxide, heated by a spirit-lamp in a glass tube, it is gradually reduced to the metallic state; but it cannot be fused. It may, however, by exposure to a white heat, be obtained in the state of grains.

It has an iron-gray colour of considerable lustre, and is 1 soft enough to yield to the file. Its specific gravity is [7:6:389] nine. When heated to redness it takes fire, swells, and is converted into green oxide. It is insoluble in sulphuric and muriatic acids, but dissolves readily in nitric acid· The solution has a lemon-yellow colour.

I. Uranium combines with two proportions of oxygen, and forms two oxides, the green and the yellow.

1. The green or protoxide is obtained by the process described at the beginning of this section, or by exposing metallic uranium to a red heat. While in grains the colour is black, but in powder it is green. It dissolves slowly in sulphuric and muriatic acids. The solution is green. In nitric acid it dissolves, but is converted into peroxide, so that the solution has a yellow colour. The protoxide is a compound of
[table]

2. The peroxide is formed when uranium or its oxide is dissolved in nitric acid. When ammonia is dropt into the solution, a beautiful yellow powder falls, which is a uraniate of ammonia. The peroxide has never yet been obtained in a separate state; but as all the compounds into which it enters are yellow, we may presume from analogy that it has the same colour. It possesses at once the characters of an acid and a base. It is composed of
[table]

The chlorides, bromides, and iodides of uranium are still unknown; nor has any thing been ascertained respecting the compounds which it may be capable of forming with hydrogen, azote, carbon, boron, silicon, phosphorus, selenium, tellurium, arsenic, antimony, or chromium.

II. Sulphuret of uranium may be obtained by passing a current of bisulphide of carbon vapour very slowly over protoxide of uranium, heated to redness in a porcelain tube. The sulphuret thus formed is black, and when rubbed assumes the metallic lustre. When heated the sulphur burns, and protoxide of uranium remains. Muriatic acid scarcely acts upon it, but nitric acid readily dissolves out the uranium, leaving the sulphur.

Sect. XV.— Of Molybdenum.

Molybdenum is procured from molybdena, a soft foliated mineral, having the metallic lustre, and similar in appearance to black leaf which occurs in isolated pieces in the primary rocks. It may be obtained from this.mineral by the following process: Roast the molybdena in a moderate heat till it is reduced to a fine powder. Dissolve this powder in ammonia, filter the solution, and evaporate to dryness. Heat the dry salt to drive off the ammonia. A white powder remains, which is oxidc of molybdenum. Mix this powder with a little oil, and expose it to a violent heat in a charcoal crucible. The metal is reduced, but not fused. It may be obtained still more readily by passing a current of dry hydrogen gas over molybdic acid while in a state of incandescence in a porcelain tube.

. Molybdenum has a silvery white colour. Its specific gravity is 8∙636. It is brittle. It is not altered though kept under water, nor is it liable to alteration from exposure to tire air. Neither dilute sulphuric, nor muriatic, nor fluoric acid dissolve it; but concentrated sulphuric acid attacks it. Nitric acid dissolves it, forming either a nitrate of molybdenum or molybdic acid, according to the proportion of acid employed. It dissolves readily in aqua regia.

I. Molybdenum combines with three different propor tions of oxygen, and forms three compounds, two of which are bases, and the third an acid.

1. The protoxide may be obtained in the following way: Dissolve a molybdate in water, and add muriatic acid to the solution till the molybdic acid at first thrown down is again dissolved. Then digest the solution with distilled zinc. It becomes first blue, then reddish brown, and at last black. After the digestion has been continued for some time, add a portion of ammonia (taking care not to add enough to throw down the zinc), and a black precipitate falls, which is the hydrated protoxide of molybdenum. It dissolves with difficulty in acids. The solution is black and opaque, but when very dilute it has a grayish-brown colour. The taste of these solutions is astringent. When heated in vacuo it parts with its water slowly. After becoming anhydrous, if we raise the temperature to incipient redness, it glows and scintillates. It is now insoluble in acids. In the open air it burns faintly at a red heat, and is converted into molybdic acid. This oxide is probably a compound of
[table]

2. Deutoxide of molybdenum may be obtained thus: Put dry molybdate of ammonia into a charcoal crucible, and expose it to a white heat. The deutoxide will be found at the bottom of the crucible. It has a crystallized appearance, a deep copper colour, and a specific gravity of 5∙666. If we mix dry molybdate of soda with sal ammoniac, and heat it rapidly in a covered platinum crucible till it ceases to exhale fumes of sal ammoniac, and after the crucible cools we wash what it contains with water, the deutoxide of molybdenum will remain in the state of a very dark-brown powder. Thus prepared, it is insoluble in acids; but it dissolves in them readily while in the state of a hydrate. In this state it is obtained by precipitating chloride of molybdenum by ammonia. It has exactly the appearance of peroxide of iron. It dissolves with a yellow colour in water. It is a compound of
[table]

3. Molybdic acid is easily obtained by exposing molybdate of ammonia to a gentle heat in an open crucible. It is a white, light, porous matter. At a red heat it melts into a deep-yellow liquid, which becomes straw-yellow on cooling. Its specific gravity is 3∙46. In close vessels it is fixed in a red heat, but in an open vessel it begins to smoke, and to be volatilized, as soon as it enters into fusion. It dissolves very sparingly in water. This acid is a compound of
[table]

II. Chlorine and molybdenum unite in three proportions analogous to the oxides.

1. When metallic molybdenum is heated in the vapour of bichloride of molybdenum, it absorbs that vapour, and is converted into a conglutinated dark-red matter, which is the protochloride· When heated to redness in vacuo, it sublimes into a dark-green matter, soluble in water and muriatic acid. The chloride is a compound of
[table]

2. When molybdenum is heated in chlorine gas, it takes [7:6:390] fire and burns, forming a dark-red vapour, which condenses in the cold part of the apparatus in dark-gray crystals, quite similar to iodine in appearance. These crystals melt when slightly heated; they sublime readily, and on cooling crystallize. In the air the matter soon deliquesces. The aqueous solution is black, but when diluted it becomes deep red, and at last yellow. This chloride is composed of
[table]

3. When anhydrous deutoxide of molybdenum is heated in dry chlorine gas, a yellowish-white sublimate rises, which is a perchloride composed of
[table]

The bromides of molybdenum are still unknown.

III. Two iodides are known analogous to the two oxides.

1. Hydrated protoxide of molybdenum dissolves in hydriodic acid, and forms a salt quite similar to the chloride.

2. In like manner hydrated deutoxide of molybdenum dissolves in hydriodic acid, and by evaporation red crystals are obtained, constituting deutoxide of molybdenum.

IV. There are three sulphides of molybdenum, all of which possess acid properties.

1. Bisulphide of molybdenum occurs native, and is well known to mineralogists under the name of molybdena. It is soft, has a leaden colour, the metallic lustre, leaves a dark-green streak on porcelain, and has a specific gravity of 4*591. It is composed of
[table]

2. Tersulphide of molybdenum maybe obtained by passing a current of sulphuretted hydrogen gas through a concentrated aqueous solution of a molybdate. On adding an acid, the tersulphide precipitates. It has a dark-brown colour while moist, but becomes black when dry. It is composed of
[table]

3. Quatersulphide of molybdenum may be obtained in the following way: Mix sulpho-molybdate of potassium with an excess of bisulphide of molybdenum, and boil the mixture for a long time in a sufficient quantity of water. At a certain period the liquid becomes muddy, and a black powder falls. This powder is to be collected on a filter, and washed with cold water. It is then washed with boiling water as long as any thing dissolves. Muriatic acid being poured into the liquid, a dark-red, translucent, bulky precipitate falls, which is to be washed on a filter. When dry it is gray, and has the metallic lustre. Its constituents arc,
[table]

The salts of molybdenum have slightly poisonous qualities.

Sect. XVI.— Of Tungsten.

This metal is usually obtained from wo∕∕ram,ablack heavy mineral, which occurs occasionally in tin mines. The following process is the easiest. Fuse together a mixture of wolfram and carbonate of potash in a crucible. Then digest the fused mass in water, which will dissolve the tungstate of potash formed. To the solution add sal ammoniac, and evaporate the whole to dryness. Heat the saline mass in a Hessian crucible till the sal ammoniac is entirely dissipated. The residual matter being now digested in water, a heavy black powder remains, which is oxide of tungsten. Boil it first in weak potash, and then in water. When this powder is heated in an open crucible it takes fire, and is converted into tungstic acid. Heat the tungstic acid to redness in a glass tube, and pass a current of dry hydrogen gas over it. The acid is reduced to metallic tungsten.

Its colour is grayish-white, and it is very hard and heavy, its specific gravity being 17∙4. The heat for melting it is so great that it can be obtained only in grains.

I. It combines with two different proportions of oxygen, and forms an oxide and an acid.

1. The oxide has a brown colour, and may be obtained by passing a current of hydrogen gas over tungstic acid, heated in a glass tube to insipient ignition. The oxide formed has a flea-brown colour. When heated in the open air it takes fire, and burns like tinder, being converted into tungstic acid. This oxide is composed of
[table]

2. Tungstic acid is obtained when the preceding oxide is exposed to a red heat. It has a pale-yellow colour. When strongly heated it becomes green, as it does also when exposed to the direct rays of the sun. Its specific gravity is 6∙12. It is tasteless, insoluble in water, but very soluble in caustic alkalies. It has the property of combining with other acids. When partially reduced it becomes blue like molybdic acid. The component parts of tungstic acid are,
[table]

II. The chlorides of tungsten, as determined by Wohler, are two in number.

1. Bichloride of tungsten is obtained when metallic tungsten is heated in a current of chlorine gas. It takes fire, and forms a chloride of a deep-red colour, which sublimes, and is deposited in the form of fine needles interlaced together. This chloride melts at a low heat, and is converted into a red vapour of a much deeper colour than the fumes of nitrous acid. Its constituents are,
[table]

2. Terchloride of tungsten may be obtained by heating oxide of tungsten in a current of chlorine gas. The oxide takes fire, leaves a residue of tungstic acid, and the chloride sublimes in yellowish-white plates, resembling native boracic acid. It has a suffocating smell, is volatile, and when exposed to the air absorbs moisture, and is converted into muriatic and tungstic acids. Hence it is composed of
[table]

III. Tungsten combines with two proportions of sulphur, forming compounds analogous to the oxide and acid of tungsten.

1. When tungstic acid is mixed with four times its [7:6:391] weight of sulphuret of mercury, and exposed to a violent heat in a crucible covered with charcoal powder, bisulphuret of tungsten is formed. It is a grayish-black powder, composed of
[table]

2. To obtain tersulphuret of tungsten, dissolve tungstic acid in a hydrosulphuret, and precipitate the liquid by adding an acid in excess. The precipitate, when washed and dried, is tersulphuret of tungsten. It is liver-brown while moist, but becomes black on drying. It is soluble in water. By heat it is converted into bisulphuret. It dissolves slowly in ammonia and the caustic fixed alkalies. Its constituents are,
[table]

Sect. XVII.— Of Columbium.

This metal, called tantalum by the Swedes, was discovered by Mr Hatchett in a black mineral from America, now distinguished by the names of tantalite and columbite. It maybe obtained from this mineral, which is very scarce, in the following way: Mix together one part of tantalite in powder, five parts of carbonate of potash, and two parts of borax, and fuse the mixture in a platinum crucible. Soften the fused mass with water, and then digest it in muriatic acid. The columbic acid only remains undissolved in the state of a white powder. Dissolve columbic acid in fluoric acid, and saturate the compound acid thus formed with potash, and evaporate the solution to dryness. When this dry salt is treated with potassium, the columbium is reduced to the metallic state.

Thus obtained, it is a black powder, which cannot be fused by the highest heat that can be raised in a wind furnace. Under the burnisher it assumes the metallic lustre, and has a yellowish-white colour. It is not altered by exposure to the air. It catches fire considerably under a red heat, glows vividly, and is converted into columbic acid. When fused with caustic potash, the metal is oxydized.

I. It combines with two proportions of oxygen, forming an oxide and an acid.

1. Columbic acid, when heated for an hour in a forge in a charcoal crucible, is converted into oxide. It is now a brownish matter, having considerable lustre, and a specific gravity of 5∙61. It is not aeted on by any acid; but when fused with caustic potash it is converted into columbic acid. Its constituents are,
[table]

2. Columbic acid may be obtained by the process given in the beginning of this section. It is a white, tasteless powder, which reddens litmus paper. When heated it gives out water, and when anhydrous it no longer acts on litmus paper. Its specific gravity is 6∙5. Its constituents are,
[table]

II. When columbium is heated in chlorine gas, it takes fire and burns brilliantly, and is converted into a vapour resembling chlorine. It condenses into a yellowish-white matter, resembling meal in appearance. When moistened with water, a hissing noise is produced, and the chloride is converted into muriatic and columbic acids. Hence it is a compound of
[table]

III. Sulphuret of columbium may be obtained by passing a current of bisulphide of carbon over columbic acid heated to whiteness. It is gray, and in powder has the metallic lustre, and some resemblance to plumbago. It feels soft, and is a conductor of electricity. When heated to incipient redness it takes fire, the sulphur burns with a blue flame, and columbic acid remains behind. It is not acted on by nitric, sulphuric, muriatic, or fluoric acid. Aqua regia decomposes it at a boiling heat. When fused with caustic potash, an orange-coloured mass is obtained, which dissolves in water, leaving sulphuret of columbium in the state of a black powder.

Sect. XVIII.— Of Titanium.

This metal, which was first discovered by Gregor, exists in the state of titanic acid in titanite or red schorl, a mineral which occurs occasionally in quartz rock. It has been found crystallized in small cubes in the slag of the hearth of various iron-works, particularly Merthyr-Tydvil in Wales.

It has a copper-red colour, and a great deal of brilliancy. It is crystallized in cubes, is hard enough to scratch rock-crystal, and has a specific gravity of 5∙3. These cubes are not acted on by acids. When heated with nitre they are rapidly oxydized. They are oxydized also rapidly when heated in caustic potash.

I. Titanium combines with two doses of oxygen, and forms an oxide which appears neutral, and an acid which unites with bases.

1. Oxide of titanium may be obtained by inclosing titanic acid in a charcoal crucible, and exposing it to a very high temperature. The external coating is metallic titanium; within is the oxide in the state of a black powder. It is insoluble in acids. When heated along with nitre it is with great difficulty converted into titanic acid. Probably the mineral called anatase is oxide of titanium.

This oxide has not been analysed. Probably it is a compound of
[table]

2. Titanic acid occurs native crystallized in right four- 1 sided prisms, and is known by the names of titanite andi rutile. It contains a little iron and manganese, from which it may be freed in the following manner: Reduce it to powder, and pass a current of sulphuretted hydrogen gas over it while heated to redness in a porcelain tube. Digest the matter thus treated in muriatic acid, and expose the residue to a red heat. It is now titanic acid~ nearly pure. Should it become red when calcined, the process must be again repeated.

It is a white, tasteless powder. When heated it becomes yellow, but resumes its white colour again when cold. It reddens litmus paper, and cannot be fused even in a white heat; but by this exposure it is rendered insoluble in acids. Its solubility may be restored by fusing it with thrice its weight of carbonate of soda, or by digesting it in concentrated sulphuric acid, in a temperature sufficiently high to drive off by degrees the excess of sulphuric acid; or we may mix it with charcoal powder, and pass a current of chlorine gas through it while heated to redness. Chloride of titanium is formed, which may be dissolved in water, and titanic acid thrown down by means [7:6:392] of ammonia. This acid is isomorphous with peroxide of tin. When in the state of hydrate it is soluble in acids, but quite insoluble in the anhydrous state. Its constitution is probably
[table]

II. Chloride of titanium may be formed by mixing titanic acid and charcoal, heating the mixture to redness, and passing a current of dry chlorine gas over it. In the receiver attached to the glass tube a liquid gradually condenses, which is chloride of titanium. When freed from all excess of chlorine by distilling it off mercury, it is transparent and colourless, does not act on mercury, and when dissolved in water is converted into muriatic acid and titanic acid. It boils at 275°. The specific gravity of its vapour, as determined by Dumas, is 6∙8055. This vapour seems to be a compound of
[table]

condensed into one volume. It is obviously a compound of
[table]

III. Sulphuret of titanium may be formed by passing vapours of bisulphide of carbon over titanic acid heated to whiteness in a porcelain tube. It has a yellow colour and the metallic lustre. It is soft and in grains, which easily spread on the skin like talc. It dissolves with difficulty in acids. When it is digested in muriatic acid, sulphuretted hydrogen gas is evolved. It is composed of
[table]

IV. When phosphate of titanium, mixed with charcoal and a little borax, is strongly heated in a well-luted crucible, it is converted into phosphuret. It is a pale-white button, brittle and granular, and does not melt before the blow-pipe.

CHAP. III.

OF SIMPLE ALKALIFIABLE BASES.

The simple alkalifiable bases at present known arc thirty-one in number. They may be arranged under the five following families.

First Family. — Alhaline Eases.

This family comprehends the seven following bodies:
[table]

The oxides of these bodies are soluble in water, and constitute the substances usually called alhalies. Second Family. — Earthy Bases.

This family comprehends the six following substances:
[table]

The oxides of these bodies are white, tasteless powders, formerly distinguished by the name of earths. Third Family. — Difficultly fused Eases.

This family comprehends the four following substances:
[table]

The oxides of these bases cannot be reduced to the metallic state by heat alone; but they readily dissolve in acids, and from this solution they cannot be precipitated in the metallic state by the introduction of zinc.

Fourth Family. — Easily fusible Eases.

This family comprehends the eight following metals:
[table]

They are all malleable metals, except bismuth, which is not very brittle. They melt at a comparatively low heat; zinc and silver require a red heat, and copper a white heat, to melt them. The rest are fused at temperatures below ignition. A rod of zinc throws down these metals from their acid solutions in the metallic state.

Fifth Family. — Noble Metals.

This family comprehends the following six metals:
[table]

They all require a violent heat to fuse them. They are insoluble in nitric acid, and their oxides arc reducible to the metallic state by the application of heat alone. We shall treat of these different families successively in this chapter.

FIRST FAMILY. ALKALINE BASES.

Sect. I.— Of Potassium;

Potassium is the basis of the alkali which has been so long familiarly known under the name of potash. It is obtained by lixiviating the ashes of vegetables which grow at a distance from the sea. The common fern contains a good deal. The salt called cream of tartar, which is deposited at the bottom of wine casks, when burnt in a crucible, leaves a black matter, which, when lixiviated with water, and the solution evaporated to dryness, constitutes carbonate of potash in a state of purity. When this carbonate is dissolved in ten times its weight of water, and boiled with its own weight of quicklime, it is rendered caustic. When cream of tartar, after being ignited in a covered crucible, is mixed with about one thirteenth of its weight of charcoal, and the mixture is exposed to a strong heat in an iron bottle, with a very wide tube fixed into it, and plunged into a receiver containing naphtha, the potash is decomposed, and potassium comes over into the receiver in the metallic state. To obtain it pure, it must be distilled over from a green glass retort, previously filled with naphtha, into a receiver, also containing naphtha. The properties of potassium were first determined by Sir H. Davy, to whom we are indebted for the discovery of the composition of the alkaline bodies.

It is a white metal, like silver. At the temperature of 50° it is a soft and malleable solid. It melts at 1361°, and at 32° it is hard and brittle, and when broken in fragments exhibits a crystalline structure. Nearly a red heat is required to convert it into vapour. Its specific gravity at 60° is 0∙86507. It is an excellent conductor of electricity[7:6:393] and of heat. When exposed to the air, it rapidly absorbs oxygen, and is converted into potash. When thrown on the surface of water, it decomposes that fluid with such rapidity that the metal takes fire, and burns with a red flarnc. When heated in oxygen gas, it burns with a brilliant white light, producing intense beat.

I. Potassium combines with two proportions of oxygen, and forms two compounds, the first of which is an alkali, the second neutral.

1. Potassium is converted into potash when put into water. It is formed also by burning potassium in oxygen gas, and continuing the heat to drive off any surplus oxygen with which it may have combined. Its colour is grayish-white, it melts at a red heat, and sublimes when the heat is raised a little higher. The fused mass is hard, breaks with a conchoidal fracture, and has a higher specific gravity than hydrate of potash. It combines with water with such violence, that if only the requisite quantity has been employed, the potash becomes red hot. After being combined with water, we cannot deprive it of that liquid by heat; it always continues a hydrate composed of
[table]

she aqueous solution of potash may be crystallized. The crystals are usually octahedrons, and are composed of
[table]

Potash has been shown to be a compound of
[table]

It is an exceedingly corrosive substance, destroying the texture both of animal and vegetable bodies. It is used to a considerable extent in medicine, and constitutes one of the most important of chemical re-agents.

2. The peroxide of potassium may be formed by heating potassium in a glass jar filled with oxygen gas. A vivid combustion takes place, and a great deal of oxygen is absorbed. It is a solid body of a yellow colour. It fuses in a high temperature, and on cooling crystallizes in plates. When put into water it effervesces, and is reduced to the state of potash. When surrounded by hydrogen and heated, the gas is absorbed without the appearance of light, and much water is formed. When hydrate of potash is fused in an open silver crucible, the peroxide of potassium is frequently formed, the oxygen of the atmosphere being absorbed, and taking the place of the water. The constituents of peroxide of potassium are,
[table]

II. When potassium is introduced into chlorine gas, it burns with a brilliant red flame, and is converted into a white salt. If potash be heated in chlorine gas, the oxygen is driven off, and the chlorine takes its place. The chloride thus formed has the taste of common salt. It dissolves readily in water, and crystallizes in right four-sided prisms with square bases. It is not altered by exposure to the air. Its constituents are,
[table]

III. When potassium is exposed to the vapour of bromine, a combination takes place. When ether impregnated with bromine is saturated with potash, cubic crystals are obtained, which constitute bromide of potassium. Its taste is sharp and rather disagreeable, but its appearance is very much that of common salt. It fuses at a red heat without decomposition. It is decomposed by sulphuric acid, and even by acetic acid, by the assistance of heat. It is composed of
[table]

IV. When potassium comes in contact with iodine, it burns with a violet-coloured flame, and is converted into iodide. The compound is white, and similar to common salt. It melts and is volatilized at a temperature below redness. On cooling it crystallizes and assumes a pearly lustre. It is composed of
[table]

V. When potassium is heated in hydrogen gas, there is a certain temperature at which the metal absorbs the gas and becomes a hydret. In this state it has a gray colour, and is destitute of the metallic lustre. It is infusible, and does not burn spontaneously either in air or oxygen gas. In water it is converted into potash, the hydrogen which it contains being disengaged along with what proceeds from the water decomposed. From the experiments of Gay-Lussac and Thenard, it appears that this hydret is a compound of
[table]

VI. When potassium is prepared from cream of tartar, a black matter remains in the retort after the distillation is over, which seems to be a compound of potassium and carbon. When moistened with a little water it takes fire and burns. When thrown into water it is decomposed with effervescence.

VII. Silicet of potassium is obtained when silica is decomposed by means of potassium. It is a brown substance, without the metallic lustre. When put into water, hydrogen gas is evolved and silica formed.

VIII. The sulphurets of potassium are no fewer than five.

1. When sulphate of potash is mixed with charcoal powder, and exposed to a white heat in a covered crucible, it is converted into sulphurct of potassium. We may obtain the same compound by passing a current of hydrogen gas over sulphate of potash heated to redness in a porcelain tube. This sulphuret has a dark-red colour like cinnabar, and is crystalline in its texture. When heated before the blowpipe it burns for an instant, but is speedily covered by a crust of sulphate of potash, which protects the interior portion from the air. This sulphuret is composed of
[table]

2. Eisulphuret of potassium may be obtained by dissolving sulphohydrate of potassium in alcohol, leaving the solution exposed to the air till it begins to become muddy on the surface, and then evaporating it to dryness in vacuo. It has an orange colour, and enters easily into fusion. It is a compound of
[table]
[7:6:394]

3. Tersulphuret of potassium is obtained by passing a current of bisulphide of carbon vapour over carbonate of potash heated to redness, as long as a permanent gas is disengaged; or we may mix thirty-five parts of carbonate of potash with twenty parts of sulphur in a glass vessel, and keeping the mixture in a state of fusion at an incipient red heat, till the ebullition produced by the escape of carbonic acid gas is at an end. This is the sulphuret usually formed when sulphur and an alkaline carbonate arc fused together. It is black and opaque while in a state of fusion, but when cold it has an hepatic colour like common liver of sulphur. It is composed of
[table]

4. Quatersulphuret of potassium may be obtained by passing the vapours of bisulphide of carbon over sulphate of potash, heated to redness till all disengagement of carbonic acid gas is at an end; or we may fuse carbonate of potash with an excess of sulphur, and, after driving off that excess by heat, pass a current of sulphuretted hydrogen over it at a red heat, till the sulphate of potash contained in it be completely decomposed. This sulphuret resembles the preceding in appearance. Its constituents are,
[table]

5. Persulphuret of potassium may be obtained by the following process. Mix together thirty-five parts of carbonate of potash and thirty-two parts of sulphur, and fuse the mixture in a glass vessel. The combination takes place at the temperature at which the sulphur fuses. This persulphuret constitutes the common liver of sulphur of chemists. To obtain it pure, we have only to take one of the preceding sulphurets, formed by means of sulphuretted hydrogen, and fuse it with an excess of sulphur, till all except what enters into combination is expelled. It has a deep liver colour, absorbs moisture from the atmosphere, and at the same time gives out the smell of sulphuretted hydrogen. When kept in badly corked phials, it becomes white on the surface, in consequence of the absorption of oxygen. When heated with metals, it converts them all without exception into sulphurets. It is composed of
[table]

IX. Selenium, when heated with potassium, combines with the evolution of a red heat. The seleniet has the metallic lustre and the colour of iron. Its fracture is crystalline and radiated. Its solution in water has a deep red colour. Acids precipitate selenium from it.

X. When potassium and phosphorus arc heated together in vacuo, they unite with the evolution of a red heat. The phosphuret has a chocolate colour. It takes fire in the open air, and when thrown into water. When the excess of phosphorus which it contains is removed by passing a current of hydrogen gas through it while heated in a glass tube, it crystallizes on cooling, has the metallic lustre, and the colour of copper.

XL Arseniet of potassium is obtained when the two metals are heated together. Light is evolved during the combination. The arseniet has a brown colour, and little of the metallic lustre.

XII. When equal weights of bitartrate of potash and antimony are intimately mixed and exposed to a strong heat, antimoniet of potassium is formed. It has a grayish-black colour, and is more porous, softer, and less brittle than antimony. When pounded it gives out sparks. When left exposed to the air it becomes hot, and burns the paper in which it has been wrapt.

Sect. II.— Of Sodium.

Sodium is the basis of soda, an alkali known to the ancients in the state of carbonate, and called by them nitre. It is found native in great quantities in Egypt, and in some other parts of Africa. But the great source of it is common salt, from which all the soda manufactured in Great Britain is made. It may be purified and rendered caustic by the same processes as potash; and it may be decomposed in the same way, and the basis of it, or sodium, may be obtained in a separate state.

Sodium is a white metal, having a colour intermediate between that of silver and lead. At the common temperature of the air it is solid and very malleable, and so soft that pieces of it may be welded together by strong pressure. It continues soft and malleable at 32°. It is an excellent conductor of electricity. Its specific gravity is 0∙97223. It melts when heated to the temperature of 194°, and requires a much higher temperature to volatilize it than potassium does. When exposed to the air it rapidly absorbs oxygen, and is converted into soda, but not so rapidly as potassium. It decomposes water and evolves hydrogen gas, but it does not take fire as potassium does. It burns with a yellowish flame, while that of potassium is reddish.

I. Like potassium, it combines with two proportions of oxygen, forming soda and peroxide of sodium.

1. Soda is formed when the metal is brought in contact with water, or when it is heated in oxygen, and the residue exposed to the requisite heat to drive off all excess of oxygen. Soda has a gray colour, is a non-conductor of electricity, has a vitreous fracture, and requires a good red heat to fuse it. Its properties are so similar to those of potash that a minute description is unnecessary. It does not deliquesce in the air like potash. Its composition is
[table]

It combines with water, and forms a hydrate, which cannot again be decomposed by heat. This hydrate is composed of
[table]

2. The peroxide of sodium is easily formed by heating sodium in oxygen gas. It has a dirty green colour, is fusible when heated, but requires a much higher temperature than peroxide of potassium for fusion. When introduced into water, it is reduced to soda, giving out the excess of oxygen which it contains. It is composed of
[table]

II. When sodium is introduced into chlorine gas, it takes fire spontaneously, and burns vividly, emitting bright red sparks. By this combustion it is converted into chloride of sodium, a substance universally known under the name of common salt. It has the well-known saline taste, and crystallizes in cubes. It is composed of
[table]

The other combinations of sodium resemble those of [7:6:395] potassium so closely, that a detailed description of them would be superfluous.

Sect. III.— Of Lithium.

Lithia, the alkali of which lithium is the base, is found in small quantities in the minerals called petalite and spodumene. From these minerals it may be extracted by the following process: ‘Mix the mineral in fine powder with a quantity of fluor spar equal to two and a half times the weight of the silica which the mineral contains. Put this mixture into a silver crucible, and make it up into a paste with sulphuric acid. Heat it at first gently, and when the greatest part of the fluosiĭicic acid has made its escape, the heat has to be raised to redness to drive off the excess of sulphuric acid, and to decompose the sulphate of alumina. The dry mass being now lixiviated with water, a solution of sulphate of lithia is obtained, mixed with a little sulphate of lime, which may be separated by careful evaporation and crystallization, or by the addition of a little oxalate of ammonia. The lithia may be thrown down from this sulphate in the state of carbonate, by means of carbonate of ammonia or carbonate of soda; or we may separate the sulphuric acid by adding barytes water, taking care to avoid all excess. The liquid being filtered and evaporated to dryness, we obtain the lithia in the state of hydrate.

Lithia thus obtained has a white colour, renders vegetable blues green, and has a taste fully as caustic as that of potash itself. At a red heat it melts and becomes a transparent liquid. When exposed to the air it does not deliquesce like potash, but remains dry; but it gradually absorbs carbonic acid, and is converted into a carbonate. It is but little soluble in water, compared with potash and soda, though the exact degree of solubility has not been ascertained. It is scarcely soluble in alcohol. When heated in a platinum crucible, it acts with considerable energy upon that metal.

Davy, by means of the galvanic battery, decomposed it, and obtained the metallic base lithium. It possesses nearly the characters of sodium. Lithia is a compound of
[table]

Its atomic weight is 1∙75, so that it is by far the lightest of alkaline bodies.

Lithium combines with chlorine, and forms a compound which may be called chloride of lithium. It has not been formed directly, but is obtained when lithia is saturated by muriatic acid, the solution evaporated to dryness, and dry salt heated in a close vessel. This chloride does not crystallize, and when exposed to the air it deliquesces rapidly. When heated it melts at a comparatively low temperature.

The other combinations of lithium have not yet been examined.

Sect. IX.— Of Barium.

Barytes, of which barium is the base, was discovered by Scheele. It exists most commonly in the state of carbonate or sulphate. It may be extracted from the sulphate by the following process: Reduce the mineral to a fine powder, mix it with the eighth part of its weight of charcoal powder, and keep it for some time red hot in a crucible, to convert it into sulphuret of barium. Dissolve the sulphuret in water, and add nitric acid to the solution. Filter and evaporate. Nitrate of barytes is obtained in octahedral crystals. Expose these crystals to a red heat in a covered platinum crucible: the nitric acid is driven off, and the barytes remains in a state of purity.

It is a grayish-white porous body, having a harsh and more caustic taste than lime, and when taken into the stomach it proves a violent poison. When heated it becomes harder, and acquires internally a bluish-green colour. Before the blowpipe on charcoal it fuses, bubbles up, and runs into globules, which penetrate the charcoal. This only happens when the barytes is in the state of hydrate. If it be anhydrous, it cannot be fused by means of the blowpipe.

When a globule of mercury in contact with moistened barytes is connected with the negative end of a galvanic battery, and the circle completed, the barytes is decomposed, and an amalgam of its base obtained. By heating this amalgam in a glass tube, the mercury is driven off, and barium obtained in a separate state. It is a white metal, of the colour of silver. It melts at a temperature below redness, and is not volatilized at a heat capable of melting plate glass. When exposed to the air it rapidly absorbs oxygen, and is converted into barytes. It decomposes water with great rapidity.

I. Barium combines with two proportions of oxygen, and forms the compounds called barytes and peroxide of barium.

1. The properties of barytes have been described at the beginning of this section. When exposed to the air it attracts moisture. It may be slaked like lime, and during the slaking is converted into a hydrate composed of
[table]

It dissolves in water; indeed boiling water dissolves more than half its weight of it; but when the solution cools, the greater part is deposited in crystals. These crystals are usually six-sided prisms. They are composed of
[table]

Barytes is a compound of
[table]

2. When dry barytes obtained from nitrate of barytes is heated in oxygen gas, it absorbs the gas rapidly. The peroxide thus formed is gray. It gives out its excess of oxygen when put into an acid liquid. We may form this peroxide by passing a current of oxygen gas over barytes heated to redness in a green glass tube, as long as it continues to absorb the gas. It is not decomposed by a red heat; but it is decomposed when put into boiling water. Its constituents are,
[table]

Chloride, bromide, and iodide of barium, are salts, which will come into view in a subsequent part of this article.

II. Barium, like potassium, combines in various proportions with sulphur; but the subject has not yet been sufficiently investigated.

1. When sulphate of barytes in powder is mixed with charcoal, and strongly heated in a well-luted crucible, it is converted into sulphuret of barium. This sulphuret dissolves in boiling water, and the solution gives fine, transparent, and colourless crystals. This sulphuret is composed of
[7:6:396]
[table]

2. If we mix caustic barytes and sulphur, and heat the mixture to redness in a covered crucible, we obtain a sulphuret of barium mixed with a little sulphate. We may obtain the sulphuret pure by passing a current of sulphuretted hydrogen gas over barytes ignited in a glass tube till all formation of water is at an end. The sulphuret formed has a brown colour.

3. When the solution of sulphuret of barium is boiled with sulphur, we obtain a compound of
[table]

III. When vapour of phosphorus is made to pass over barytes in a glass or porcelain tube, five sevenths of the barytes are reduced to the metallic state, and combine with phosphorus, while two sevenths remain unaltered, and combine with phosphoric acid formed during the process. The colour of the pħosphuret is dark brown, and its lustre almost metallic.

Sect. V.— Of Strontium.

Strontian, like barytes, occurs usually in the state of carbonate or phosphate. It may be obtained in a separate state by the same processes as those which were described in the last section for procuring barytes. It may be decomposed in the same way as barytes, and its metallic basis, called strontium, obtained in a separate state.

. Strontium is a white solid metal, much heavier than water, which bears a close resemblance to barium in its properties. By exposure to the air, or by coming in contact with water, it is immediately converted into strontian.

I. Strontium, like barium, combines with two proportions of oxygen, and forms strontian and peroxide of strontium.

1. Strontian obtained from the nitrate by heat is a porous mass of a grayish-white colour, which converts vegetable blues into green, has an acrid taste, and is soluble in water. It maybe slaked like lime, falling into a white powder composed of
[table]

It dissolves abundantly in hot water, and, as the solution cools, is deposited in large crystals, which are right square prisms. They are composed of
[table]

Strontian has the property of tinging flame of a beautiful red colour. The colour is very well seen when a solution of chloride of strontian in alcohol is allowed to burn in a platinum cup while we stir the liquid with a spatula. Barytes and soda give a yellow tinge to flame. Lime gives a red tinge, but lighter than the colour communicated by strontian.

Strontian is a compound of
[table]

Strontian is not poisonous, as is the case with barytes.

2. Peroxide of strontium is obtained in bright scales when strontian water is mixed with deutoxide of hydro gen. Its properties are similar to those of peroxide of barium, but it is more easily dried. It is composed of
[table]

The chloride, bromide, and iodide of strontian, are salts which will be described afterwards. The sulphuret and phosphuret of strontium resemble those of barium so closely that a detailed description of them appears unnecessary.

Sect. VI.— Of Calcium.

Lime occurs in such quantities, and is of so much importance, that it has been known and employed from the remotest ages. It occurs always in combination with an acid, most commonly with the carbonic, constituting limestone, marble, calcareous spar, chalk, frequently with sulphuric acid, constituting gypsum, selenite, sulphate of lime. It is found also combined with phosphoric acid, fluoric acid, arsenic acid, tungstic acid, and silicic acid.

It may be obtained pure by exposing calcareous spar or pure white marble to a white heat in a covered crucible. Indeed the common process of burning lime yields pure lime, provided the limestone employed be free from impurities. Pure lime is of a white colour, moderately hard, but easily reduced to powder. It has a caustic taste, corrodes animal and vegetable bodies, and has a specific gravity of 3Ό8. By a process similar to that described when treating of the decomposition of barytes, in the fourth section of this chapter, it may be decomposed, and its metallic basis, to which the name of calcium has been given, obtained in a separate state.

Calcium is white like silver, solid, and much heavier than water. When heated in the open air it burns brilliantly, and quicklime is produced.

I. Calcium, like the other alkaline bases belonging to this family, combines in two proportions with oxygen, and forms the two substances called lime and peroxide of calcium.

1. Lime cannot be fused by the greatest heat of our furnaces; but before the oxygen and hydrogen blowpipe it maybe fused in small particles into a brilliant limpid glass, and during the fusion a beautiful lambent flame of an amethystine hue makes its appearance. When water is sprinkled on newly burnt lime it swells, great heat is produced, the water disappears, and the lime is resolved into a very fine powder. This process is called slaking lime. The lime combines with and solidifies the water; hence the heat evolved, and the reduction of the lime to a fine powder. Slaked lime is a compound of
[table]

Water dissolves a little lime, and the solution has been long known by the name of lime water. Cold water dissolves more lime than hot water. At the temperature of 60°, 758 grains of water dissolve one grain of lime. When this solution is concentrated in vacuo over sulphuric acid, the lime crystallizes, and is deposited in small six-sided prisms. These crystals, doubtless, consist of lime united to a greater proportion of water than in slaked lime, but they have not yet been subjected to analysis.

The atomic weight of lime is 3∙5, and it is a compound of
[table]
[7:6:397]

2. Peroxide of calcium may be formed by letting fall, drop by drop, lime water into deutoxide of hydrogen. Small brilliant scales fall, which constitute the peroxide of calcium. It undergoes spontaneous decomposition when kept under water, and cannot be dried in vacuo without losing its excess of oxygen. Its constituents are,
[table]

II. The chloride, bromide, and iodide of calcium are salts which will be described in a subsequent part of this article.

Lime has the property of combining with chlorine, and of forming an important compound, to which the name of chloride of lime has been given. It was first made by Messrs Tennant and M 4 Intosh of Glasgow, and has now become an important article of commerce under the name of bleaching powder. It is made by leaving slaked lime in a chamber kept full of chlorine gas till it refuses to absorb any more. It is a white powder, having a hot taste, and readily soluble in water. It has the property of destroying vegetable colours, and is in consequence employed extensively in bleaching. When exposed to the air it is gradually converted into chloride of calcium.

III. Three different compounds of sulphur and calcium have been examined by chemists.

1. When sulphate of lime in powder is mixed with about one fifth of its weight of charcoal powder, and exposed for a couple of hours to a white heat in a covered crucible, it is converted into sulphuret of calcium. Its colour is reddish. It dissolves imperfectly in water, but with great ease in muriatic acid, while a great quantity of sulphuretted hydrogen gas is evolved. It is a compound of
[table]

This sulphuret is obtained (but mixed with sulphate of lime) when a mixture of sulphur and limc is cautiously heated to redness in a covered crucible. In this state it is known by the name of Canton’s phosphorus.

2. Bisulphuret of calcium may be obtained by boiling a mixture of slaked lime, sulphur, and water, and allowing the liquid to cool slowly before it be perfectly saturated with sulphur. Yellow-coloured crystals separate, which constitute the bisulphuret∙ They require 400 times their weight of water at 60° to dissolve them, but they are more soluble in boiling water. The bisulphurct is a compound of
[table]

The crystals consist of
[table]

3. When sulphuret of calcium is boiled in water with sulphur till it refuses to take up any more, we obtain a persulphuret of calcium, composed of
[table]

This sulphuret was proposed many years ago as a substitute for potash ley in bleaching; but the proposal was unsuccessful.

IV. Phosphuret of calcium may be prepared in the same way as phosphuret of barium. It has a deep-brown colour. It is insoluble in water, but decomposes that liquid, and phosphuretted hydrogen gas is disengaged abun- i dantly. It falls to pieces in the air, and is soon destroyed by the action of the atmosphere.

Sect. VII.— Of Magnesium.

Magnesia, like lime, is found native in considerable quantity, sometimes united to water, sometimes to carbonic acid; and it exists in sea-water in combination with sulphuric and muriatic acids. From the carbonate it is easily obtained pure by simple exposure to a red heat. From sea-water, after the common salt and lime are separated, it is easily thrown down (at a boiling temperature) by carbonate of soda. The white precipitate, after being washed, dried, and ignited, is pure magnesia.

Magnesia may be decomposed by the same process as the other alkaline earths, and its basis magnesium obtained in a separate state. Μ. Bussey has lately ascertained, that when the vapour of potassium is passed over chloride of magnesium heated to redness in a porcelain tube, the magnesium is disengaged, and may be collected on a filter. In this state it is in brown flocks, which, when rubbed in an agate mortar, assume the metallic lustre, and resemble lead in appearance. It is not attacked by dilute nitric acid, but is dissolved in muriatic acid. When heated before the blowpipe, it takes fire, and is converted into magnesia. It has not the property of decomposing water, like the bases of the other alkaline earths.

I. We know at present only one compound of magnesium and oxygen, namely, magnesia.

Magnesia is a white, soft, elastic, tasteless powder, not sensibly soluble in water, and slowly changing vegetable blues to green. It cannot be melted by the strongest heat which we can apply. Dr Clarke, by means of the oxygen and hydrogen blowpipe, fused it with great difficulty into a white enamel.

It does not combine with water, like the other alkaline earths, hence it cannot be slaked like lime; nor does it become hot when water is poured on it. Yet it is found native in the state of a hydrate, composed of
[table]

It has a strong affinity for silica. It does not absorb carbonic acid from the atmosphere. Magnesia is a compound of
[table]

II. When heated in chlorine gas, magnesia parts with its oxygen, and is converted into chloride of magnesium, a salt to be described in a subsequent part of this article. The bromide and iodide of magnesium are likewise salts.

III. No accurate experiments have hitherto been made upon the formation of sulphuret of magnesium.

The oxides of the seven metals described in the preceding sections constitute the most powerful alkaline bodies. They all combine readily with acids, and form salts. The chlorides, bromides, and iodides of these bodies are also salts. The order of the affinity of these bodies fin-acids is as follows :—Barytes, strontian, potash, soda, lime, lithia? and magnesia. But to this order there are some exceptions. For example, lime unites to oxalic acid in preference to the other bases when they are all in solution together.
[7:6:398]

FAMILY SECOND. EARTHY BASES.

Sect. I.— Of Aluminum.

Alumina, which is in fact an oxide of aluminum, is an essential constituent of clay, and constitutes the basis of alum, from which it may be obtained in the following manner. To a solution of alum in water add carbonate of soda, and digest for some time. Then filter, to separate the precipitate that has fallen. Wash it well on a filter, and dissolve it in muriatic acid. Precipitate the alumina from this solution by carbonate of ammonia, and digest the precipitate in a solution of carbonate of ammonia, to remove the muriatic acid as completely as possible. Then wash it and dry it. Alumina may be obtained from ammoniacal alum by simple exposure to a strong heat.

When dry alumina is intimately mixed with charcoal powder, and a current of dry chlorine gas is passed over the mixture while heated to redness in a porcelain tube, chloride of aluminum is gradually formed, which sublimes, and at last obstructs the farther extremity of the porcelain tube. When this chloride, which is a solid body, is mixed with about equal parts of potassium in a platinum crucible, and after the lid is tied down with a wire, the heat of a spirit-lamp is applied, the mixture becomes suddenly intensely hot, and the potassium unites with the chlorine, leaving the aluminum in a state of purity. When the crucible is cold it is to be plunged into cold water, to dissolve out the potash, and prevent it from acting on the aluminum. Then collect the aluminum on a filter; wash it and dry it.

. Aluminum obtained by this process has a considerable resemblance to platinum. When burnished it assumes the metallic lustre, and splendour of tin. The scales admit of compression, so that alumina seems to be a malleable metal. It is not fusible at the temperature at which cast iron melts. When exposed to a strong heat, surrounded by charcoal powder, it undergoes no alteration. W hile in powder it is a non-conductor of electricity; but this is the ease with iron also when in the same state. At a red heat it burns with great splendour, and is converted into alumina. The heat produced by the combustion is so intense that the alumina is fused into a button hard enough to cut glass, almost as hard, indeed, as sapphire. Aluminum is not altered by water at common temperatures, but when the water is boiling hot it is very slowly decomposed. It is not attacked by sulphuric or nitric acid while cold; but when heated it dissolves rapidly in sulphuric acid, sulphurous acid being evolved. In dilute sulphuric acid, and in muriatic acid, it dissolves with the evolution of hydrogen gas. It dissolves also with the same evolution in very dilute solutions of potash, and even of ammonia. When heated in chlorine gas it burns, and is converted into chloride of aluminum.

I. So far as is known at present, aluminum unites with only one proportion of oxygen, and forms the well-known base named alumina.

Alumina is a fine white powder, destitute of taste and smell, but adhering strongly to the tongue. It is insoluble in water and alcohol. It dissolves readily in caustic potash or soda while in the state of a hydrate. Even liquid ammonia dissolves a small quantity of it in that state. Even after ignition, it dissolves slowly in sulphurie and muriatic acids when assisted by heat. If to the sulphuric acid solution of it we add some sulphate of potash, octahedral crystals of alum are speedily deposited. At the violent heat produced by the oxygen-hydrogen blowpipe, it may be fused into a white semitransparent enamel. Its spceifie gravity is 4∙200. Alumina is a compound of
[table]

Though alumina be insoluble in water, yet its affinity for that liquid is considerable. When dry alumina is exposed to a moist atmosphere, it increases in weight about 15 per cent, by absorbing moisture. Hydrate of alumina occurs native. It is a white stalactitical-looking substance, distinguished among mineralogists by the name of gibsite. It is composed of
[table]

When we precipitate alumina from its solution in potash, and, after washingit, allow it to dry spontaneously in the open air, the white powder obtained is a compound of
[table]

When we dry this bihydrate at a temperature of 100°, it is converted into a simple hydrate. The mineral called diaspore is a dihydrate, or a compound of
[table]

Alumina is one of the weakest of the bases. It even seems to perform the part of an acid in certain combinations which occur in the mineral kingdom. Thus Spinell is a compound of one atom magnesia and six atoms alumina. The magnesia undoubtedly acts the part of the base in this mineral, so that alumina is the acid. The affinity between alumina and magnesia is very great. Hence in chemical analyses we sometimes get a compound of the two. It is easily distinguished from pure alumina by theproperty which it has of becoming hot when moistened with water.

II. The mode of obtaining the chloride of aluminum has been stated at the beginning of this section. It is a solid crystalline body, having a pale-yellow colour, semitransparent, and in plates. In the air it smokes feebly, and soon deliquesces. In water it dissolves with the evolution of great heat. It is volatilized at a temperature not much higher than that of boiling water. Though this chloride has not been analysed, there can be little doubt that its constituents are,
[table]

The bromide and iodide of aluminum are still unknown. IV. Sulphur may be distilled off aluminum without any combination taking place; but if the vapour of sulphur be passed over aluminum in a good red heat, the combination takes place with a very vivid combustion. Sulphuret of aluminum is black, semimetallic, and acquires lustre when burnished. When left in the air it emits a strong smell of sulphuretted hydrogen, and falls at last into a grayish-white powder. When it is thrown into water, sulphuret of hydrogen is given out rapidly, and alumina precipitates. Hence its constituents are evidently
[table]

V. Seleniet of aluminum may be formed in the same way as the sulphuret. Its properties are very similar to those of the sulphuret.
[7:6:399]

VI. When aluminum is ignited in an atmosphere of phosphorus, it burns brilliantly. The phosphuret formed is a powder of a grayish-black colour, which acquires the metallie lustre when burnished, and emits the smell of phosphuretted hydrogen gas.

VII. When arsenic and aluminum are heated together, they combine with a feeble evolution of heat. The arseniet is a black powder, which assumes the metallic lustre when burnished, and emits the smell of arsenietted hydrogen gas.

Sect. II.— Of Glucinum.

Glucina, which is the oxide of glueinum, exists to the amount of about fourteen per cent, in the beryl or emerald, from which it may be extracted by the following process: Fuse pounded beryl with thrice its weight of earbonate of soda for an hour in a platinum crucible. Dissolve the fused mass in muriatic acid, evaporate to dryness, digest the residue in muriatic acid, which will dissolve every thing but the silica. Collect the silica on a filter, wash it well, and set it aside. The liquid which passes through is to be reduced by evaporation to a small quantity. It contains alumina and glucina in solution in muriatic acid. Precipitate these two bodies by carbonate of ammonia. Put the precipitate into a phial with a ground stopper, and fill up the phial with solution of carbonate of ammonia. Put in the stopper, and agitate the contents of the phial frequently for the space of twenty-four hours. The glucina will be dissolved by the carbonate of ammonia, but the alumina remains in the state of a white matter. Separate it by the filter, and boil the liquid containing the glucina till the earbonate of ammonia is driven off. A white powder falls down, which, when washed and dried, is glucina.

Glucina may be converted into chloride of glucinum, and the glucinum obtained in a separate state, by exactly the same method which was given in the last section for obtaining aluminum.

'∙ Glucinum obtained in this way is a dark-gray powder, which when burnished acquires the metallie lustre. It is very difficult of fusion. It does not absorb oxygen at the ordinary temperature of the atmosphere, and it may be kept even in boiling water without alteration. When heated in air or oxygen gas it burns with much splendour, and is converted into glucina. It dissolves in concentrated sulphuric acid when assisted by heat, and sulphurous acid is exhaled. In dilute sulphuric and muriatic acids it dissolves readily with the evolution of hydrogen gas, and in nitric acid with the evolution of deutoxide of azote. It dissolves also in potash ley, but not in ammonia.

I. So far as we know at present, glucinum combines with only one dose of oxygen, and forms the well-known base called glucina.

Glucina is a soft, light, white powder, without either taste or smell, which has the property of adhering strongly to the tongue. Its specific gravity is 2∙976. It is insoluble in water, but with a small quantity of that liquid it forms a paste which has some ductility. It is soluble in potash and caustic ley, in this respect resembling alumina. It is insoluble in liquid ammonia, but dissolves readily in carbonate of ammonia. By this property it can be easily separated from alumina. It combines with acids and forms sweet-tasted salts; hence the reason why it was called glucina^[10. From yλwMsi, sweet. ] by Vauquelin, the discoverer of it. Its atomie weight is 3∙25, and it is composed of
[table]

Hydrate of glueina is obtained when we precipitate glueina from muriatic acid by ammonia added in excess. It is a bulky, white powder, similar to hydrate of alumina. The quantity of water which it contains has not yet been determined.

II. Chloride of glueinum may be formed by passing a current of chlorine gas over an intimate mixture of glucina and charcoal, heated to redness in a porcelain or glass tube. The chloride sublimes in the form of white needles. It is very volatile, and deliquesces speedily when exposed to the air. Glueinum, when heated in chlorine gas, burns with splendour, and is converted into the same chloride.

III. When glucinum is heated in the vapour of bromine, it takes fire, and is converted into bromide. It is in long white needles, is very volatile and fusible, and dissolves in water with the evolution of much heat.

IV. Iodide of glucinum may be formed by a similar process. It is also in long white needles, and resembles the two preceding compounds.

V. When glueinum is heated in the vapour of sulphur, it burns with almost as much splendour as in oxygen gas. The sulphuret is a gray mass, which has not undergone fusion. It dissolves in water with difficulty, and without the evolution of sulphuretted hydrogen gas; but when an acid is added, that gas is given out abundantly.

VI. Seleniet of glucinum may be made by a similar process as the preceding. The seleniet fuses into a gray mass having a crystalline texture. It dissolves with difficulty in water, and the solution is red, from the selenium disengaged.

VII. Glucinum burns when heated in the vapour of phosphorus. The phosphuret is gray, and when put intoι water phosphuretted hydrogen gas is evolved.

VIII. When glucinum is heated along with arsenie, light, is evolved. The arseniet formed is a gray powder, which has not undergone fusion, and which, when put into water, disengages arsenietted hydrogan gas.

Tclluret of glucinum is similar in appearance to arseniet.

Sect. III.— Of Yttrium.

Yttria, which constitutes the oxide of yttrium, is obtained from a scarce mineral called gadolinite, of a black colour, a glassy lustre, and a specific gravity of 4∙2'37, which has hitherto been found only in Sweden. The process is as follows: Digest the pounded mineral in nitro-niuriatic acid till it is completely decomposed. When the solution is filtered, the silica contained in the mineral is left behind. The solution contains yttria, glucina, eerium, and oxide of iron. Evaporate it to dryness, to get rid of all excess of acid, and dissolve it by digestion in distilled water. To this solution add oxalic acid as long as any precipitate continues to fall, and until the precipitate becomes of a perfectly white colour. The yttria and oxide of cerium are precipitated, while the glucina and oxide of iron remain in solution. The precipitate is a beautiful white light powder. Let it be ignited to decompose the oxalie acid; then dissolve the residual mass in muriatic acid, and put a quantity of sulphate of potash into the solution, considerably greater than can be dissolved. In twenty-four hours the cerium is precipitated in the state of a white powder, while the yttria remains in solution. The [7:6:400] yttria may now be precipitated by pure ammonia, and washed and dried. Gadolinite yields about 44ļ per cent, of yttria.

Yttria may be decomposed, and yttrium extracted from it, by precisely the same process which furnishes aluminum and glucinum.

Yttrium thus obtained is in small scales, having the metallic lustre and the colour of iron. It is brittle, and does not oxydize at the ordinary temperature in the air or in water. When heated to redness, it burns, and is converted into yttria. When the combustion takes place in oxygen gas, its splendour can scarcely be surpassed. The yttria obtained is white, and exhibits evident marks of having been fused. Yttrium dissolves readily in dilute sulphuric acid, with the evolution of hydrogen gas. It dissolves with more difficulty in potash ley, and not at all in ammonia.

I. So far as we know at present, yttrium combines with only one dose of oxygen, and forms yttria, which is a fine white powder, destitute of taste and smell. Its specific gravity is 4 ’ 842. It is insoluble in water, but, like alumina, it retains a large quantity of that liquid. It is insoluble in potash and soda leys, which distinguishes it from alumina and glucina; but it dissolves in carbonate of ammonia, and in the other alkaline carbonates; but glucina is much more soluble in carbonate of ammonia than yttria. Its atomic weight appears to be 5∙5, and it is a compound of
[table]

II. Chloride of yttrium is easily obtained by passing a current of dry chlorine gas over a mixture of yttria and charcoal exposed to a red heat in a porcelain or glass tube. It has a strong resemblance to chloride of glucinum, being in white brilliant needles, which easily melt into a white crystalline mass. It is volatile, dissolves in water with the evolution of much heat, and speedily deliquesces in the air.

The bromide and iodide of yttrium still remain to be examined.

III. When yttria is heated in the vapour of sulphur, it takes fire, and forms a gray powder, which is insoluble in water, and does not undergo spontaneous decomposition. It dissolves in acids with the evolution of sulphuretted hydrogen gas.

IV. When yttrium is heated with selenium till that substance fuses, a feeble incandescence takes place. The seleniet formed is black, and does not decompose water; but when put into dilute acids, selenietted hydrogen gas is given out.

V. In the vapour of phosphorus yttrium combines with a lively combustion. The phosphuret is a grayish-black powder, which gives out phosphuretted hydrogen when put into water.

Sect. IV.— Of Cerium.

This metal, or at least its oxide, exists in a reddish-coloured mineral found in Sweden, and distinguished by the name of cerite. It may be obtained by digesting the pounded mineral in nitric aċid, neutralizing the solution, and adding oxalate of ammonia. A white precipitate falls, which is oxalate of cerium. When heated the oxalic acid is destroyed, and oxide of cerium remains. When this oxide is converted into chloride by a process similar to that described in the first section of this family, while treating of chloride of aluminum, and afterwards decomposing this chloride by potassium, cerium is obtained in the metallic state.

Thus obtained, cerium is a gray powder, having the metallic lustre; but its peculiar properties have not yet been determined.

I. Cerium combines with two proportions of oxygen, and forms two oxides, both of which possess the characters of bases. The protoxide, when in the state of a carbonate, is white; the peroxide is yellow or brownish-red.

1. The peroxide is obtained when the oxalate of cerium is heated to redness in an open vessel. Thus obtained, it has a reddish-brown colour, is tasteless, and may be exposed to a strong heat without undergoing any alteration. When we digest it in muriatic acid, chlorine is disengaged, and the solution becomes less and less coloured, till at last it has only a slight flesh-red colour. The reason of this is, that the peroxide, by the action of the muriatic acid, is gradually converted into protoxide. The protoxide may be thrown down from the muriatic solution, by carbonate of ammonia, in the state of a carbonate. It is then a white, soft, tasteless powder, which dissolves readily in acids. The salts which it forms have a sweet taste, like those of yttria. Indeed they resemble the salts of yttria so closely in all their properties, that it is exceedingly difficult to distinguish the one from the other. From the recent experiments of Dr Steel, it would appear that the atomic weights of cerium and its oxides are as follows:
[table]

II. There are two chlorides of cerium, but they have not yet been carefully examined. The protochloride is obtained when oxide of cerium is digested in muriatic acid till the solution becomes almost colourless. It crystallizes with difficulty in four-sided prisms. It deliquesces in the air, is very soluble in water, and also in alcohol, and the alcoholic solution burns with a yellow-coloured flame.

The perchloride is a reddish-yellow solution, which gelatinises by cautious evaporation. It does not crystallize, and when heated is gradually converted into protochloride.

The bromides and iodides of cerium are still unknown.

III. It would appear, from Laugier’s experiments, that cerium combines with carbon. The carburet is obtained when protocarbonate of cerium is made into a paste with oil, and heated in a retort surrounded by charcoal. It is a black matter, which takes fire spontaneously when exposed to the air.

IV. Sulphuret of cerium may be formed by passing the vapour of bisulphide of carbon over oxide of cerium heated to redness in a porcelain tube. It is light and porous, and similar to red lead in colour.

When oxide of cerium is mixed with alkaline hepar in great excess, and exposed to a white heat in a covered crucible, and the hepar afterwards washed off with water, a sulphuret of cerium remains in brilliant scales, like mosaic gold in appearance.

V. When a stick of phosphorus is put into a solution of cerium in muriatic acid, and kept for some days on a stove, the bottom and sides of the vessel are covered with a white precipitate. The phosphorus itself becomes coated with a hard brown crust, which was tenacious, and shone in the dark., When heated it took fire, and left a small quantity of oxide of cerium.

Sect. V.— Of Zirconium.

Zirconia, which constitutes, an oxide of zirconium, exists as a constituent of the zircon or hyacinth, a dark red-coloured hard mineral, having a specific gravity of 4∙7. To obtain zirconia from this mineral, reduce it to a fine powder, mix it with thrice its weight of potash, and fuse it in [7:6:401] a platinum crucible. Digest the fused mass in water till all the potash is abstracted; then dissolve it as far as possible in muriatic acid. Boil the solution, to precipitate any silica that may have been dissolved; then filter, and add a quantity of potash. The zirconia precipitates in the state of a white powder.

Zirconia thus obtained may be dissolved in fluoric acid, and by the addition of the requisite quantity of potash or fluoride of potassium, and evaporation, we may obtain the salt called potashfluate of zirconia. Reduce this salt to powder, and render it anhydrous by exposure to heat. Then mix it in an iron tube with potassium, the two substances being introduced in alternate layers. Hcat the tube till the potassium melts, and then mix the two substances by means of an iron wire. Shut the mouth of the tube, and heat it over a spirit-lamp till it begins to get red hot. The zirconia is reduced in the tube, and converted into zirconium, which remains mixed with a quantity of fluate of potash. Allow the tube to cool, and then wash out its contents with water. The fluate of potash dissolves, and the zirconium falls to the bottom of the vessel in the state of a black powder.

Thus obtained, it has a close resemblance to charcoal powder. Though rubbed by a burnisher, it does not acquire the metallic lustre. To free it from some hydrate of zirconia with which it is mixed, it may be kept for five or six hours in dilute muriatic acid at the temperature of 100°. Then wash the zirconium first in a solution of sal ammoniac, and afterwards in alcohol.

Thus purified, zirconium has some resemblance to plumbago, being composed of brilliant scales. It is a non-conductor of electricity. When heated in hydrogen gas, or in vacuo, it is not altered. It does not fuse even in a strong heat. When heated in the open air it takes fire long before it is red hot, burns quietly, and is converted into zirconia, which is perfectly white. When it contains hydrate of zirconia it burns with a kind of explosion, which throws every thing out of the tube. When mixed with chlorate of potash it takes fire when violently struck, but burns without detonating. In fused nitre it does not burn at a heat below redness. When mixed with carbonate of potash it burns at the expense of the carbonic acid with a feeble disengagement of light. It burns also in melted borax, in consequence of the water which the salt retains. For the same reason it burns in the alkaline hydrates. At the ordinary temperature it is not acted on by sulphuric or muriatic acid. Even when long boiled in these acids the action is very small. Neither nitric acid nor aqua regia is capable of dissolving it; but it dissolves readily in fluoric acid, with the disengagement of hydrogen gas. A mixture ofnitric and fluoric acid dissolves it with great rapidity. It does not dissolve in caustic alkaline leys.

I. We know only one compound which it is capable of forming with oxygen, namely, zirconia.

Zirconia is a white powder, which feels somewhat harsh when rubbed between the fingers. It has neither taste nor smell. It is infusible before the blowpipe, but when heated violently in a charcoal crucible it undergoes a kind of imperfect fusion, acquires a gray colour, and something of the appearance of porcelain. In this state it is very hard, has a specific gravity of 4*3, and is no longer soluble in acids. Zirconia, though insoluble in water, has a considerable affinity for that liquid. When dried in the open air, after precipitation, it retains about one third of its weight of water, and assumes a grayish-yellow colour, and a certain degree of transparency, which gives it some resemblance to common glue. This hydrate is probably composed of
[table]

After ignition zirconia is insoluble in acids, except concentrated sulphuric acid by digestion, in which it maybe dissolved. It recovers its solubility likewise when ignited with potash. The hydrate of zirconia is a white bulky semigelatinous matter, which dissolves readily in acids while moist, but after being dried it dissolves but slowly. It contracts much in drying. It begins to glow like a live coal when heated nearly to redness. It dissolves in small quantity, and very slowly, in carbonate of ammonia. It is insoluble in the fixed alkaline carbonates; but if we precipitate a salt of zirconia with earbonate of potash, and add an excess of the carbonate, the precipitate redissolves. The experiment succeeds still better with bicarbonate of potash. Zirconia is insoluble in potash or soda ley.

We are not in possession of accurate experiments to determine the atomic weight of zirconia. From Berzelius’s analysis of the sulphate of zirconia, it follows that the atomic weight of zirconia is 3∙75. Hence we may conclude that it is a compound of
[table]

II. When zirconium is heated in chlorine gas it takes fire, and is converted into a white fixed matter, which is chloride of zirconium.

The bromide and iodide of zireonium are still unknown.

III. When zireonium is obtained by means of potassium containing carbon, it seems to be in the state of a carburet; for when digested in muriatic acid it gives out a smell similar to that of cast iron when so treated. When calcined the zirconia obtained is gray, and it is extremely difficult to burn out the carbon.

IV. Sulphuret of zirconium is formed whtíň the two constituents arc mixed and heated in vacuo, or surrounded with hydrogen gas. At the instant of combination a feeble light is evolved. This sulphuret is a powder of a deep-brown colour, which does not acquire lustre under the burnisher. It is insoluble in sulphuric, nitric, and muriatic acids. Aqua regia dissolves it slowly at a boiling heat. Fluoric acid dissolves it rapidly, while sulphuretted hydrogen is given out. It is not dissolved by caustic potash. When fused with hydrate of potash we obtain sulphuret of potassium and zirconia.

Sect. VI.— Of Tìiorìum.

Thorina, which constitutes an oxide of thorium, has been hitherto found only in a black mineral from the neighbourhood of Christiania, in Norway, to which the name of thorite has been given. It resembles obsidian, but has a specific gravity of 4∙63. From this mineral it may be obtained by the following process:

Reduce the mineral to powder, and digest it in muriatic acid till it is dissolved. Evaporate the solution to dryness, and digest the residue in muriatic acid, and filter to get rid of the silica. Caustic ammonia added to the liquid rather in excess precipitates the thorina still contaminated with various foreign bodies. Dissolve the precipitate while still moist in muriatic acid, and pass a current of sulphuretted hydrogen gas through the liquid to throw down a little tin and lead which it contains. Evaporate gently to dryness, redissolve in water, and precipitate again by caustic potash added in excess to retain in solution a little alumina which is present. Dissolve the new precipitate in muriatic acid, neutralize with caustic ammonia, and then add as much sulphate of potash as the liquid is capable of dissolving. A fine white powder falls. Collect it on a filter, and wash it with a saturated solution of sulphate of potash. Dissolve this powder in boiling water, and add potash to the solution, thorina falls [7:6:402] in the state of a white powder, which may be washed and dried.

When thorina is mixed with charcoal powder and heated to redness in a porcelain tube, while a current of chlorine gas passes over it, chloride of thorium is obtained. When this chloride is mixed with potassium and heated in a platinum crucible, a slight detonation takes place, heat, but no light, being evolved. The thorium is reduced. By washing it with water the chloride of potassium is separated, and thorium remains in the state of an iron-gray coloured powder having the metallic lustre. Like aluminum, it appears to be malleable. It is not oxydized by water, even when assisted by heat. When gently heated in the open air it burns with much splendour, and is converted into thorina. Sulphuric acid acts upon it very feebly, and nitric acid exhibits still less energy; but muriatic acid dissolves it rapidly with the evolution of hydrogen gas, if we assist the action by heat. It is not acted on by caustic alkalies.

I. The only known compound of thorium and oxygen is thorina, which may be obtained in the state of a hydrate by adding caustic potash to the solution of thorina in an acid.

Hydrate of thorina is gelatinous, falls rapidly, and contracts much while drying. While moist it dissolves rapidly in acids, but much more slowly when dry. The salts which it forms have a styptic taste. The hydrate is insoluble in the caustic alkalies; but it dissolves in the carbonates, and the solubility increases with the concentration of these liquids. It is more soluble in cold than in hot carbonate of ammonia. Ammonia does not precipitate thorina from a saturated solution in carbonate of ammonia, as it does zirconia. When this hydrate is strongly heated, it gives out its water, and becomes very hard, and difficult to pulverize. In this state it is soluble in no acid but the sulphuric. It is not rendered soluble in acids by calcining it with a caustic or carbonated alkali. When the alkali is extracted after such a calcination, the thorina cannot be washed with pure water, but forms with it a milky liquid, which passes through the filter. The atomic weight of thorina seems to be 8 - 5, and we may conclude from analogy that it is a compound of
[table]

Thorina is distinguished from the other earths by the following properties:

1. Its sulphate is precipitated from its solution by raising it to the boiling temperature, and dissolves again, though slowly, in cold water. This property is peculiar to thorina.

2. It is insoluble in caustic alkaline leys, which distinguishes it from alumina and głucina.

3. It forms with potash a double sulphate, which is soluble in water, but insoluble in a saturated solution of sulphate of potash. This distinguishes it from yttria.

4. Zirconia forms a similar double sulphate with potash, but it is almost wholly insoluble in cold water. This distinguishes it from thorina. Besides, the salts of thorina are precipitated by prussiate of potash, which is not the case with the salts of zirconia.

5. From the protoxide of cerium it is distinguished by not becoming reddish brown, but continuing white, when it is calcined; and by not forming a coloured bead before the blowpipe, either with borax or with biphosphate of soda.

II. Chloride of thorium is formed by the process described at the beginning of this section. We are still ignorant of its properties.

III. Sulphuret of thorium is formed when a mixture of the two constituents is heated in a close vessel, and brilliant combustion accompanies the combination. The sulphuret is brown, acquires brilliancy when burnished, but never assumes the metallic lustre. When heated in hydrogen gas it undergoes no alteration. In the open air the sulphur may be sublimed by heat, and the thorium is converted into thorina. It is scarcely acted on by sulphuric, nitric, or muriatic acids, even when the action is assisted by heat. Aqua regia dissolves it completely by the assistance of heat, and converts it into sulphate of thorina.

IV. Phosphuret is formed when thorium is heated in the vapour of phosphorus. The combination is accompanied by the evolution of light. The phosphuret has a gray colour, and the metallic lustre; and has some resemblance to plumbago. It is not altered by water; but when heated it takes fire, and is converted into phosphate.

THIRD FAMILY.—DIFFICULTLY FUSIBLE BASES.

This family includes some of the most useful bodies in existence.

Sect. I.— Of Iron.

Iron is one of the seven metals with which the ancients were acquainted.^[11. These were gold, silver, copper, iron, tin, lead, and mercury. ] Its ores are abundant, but the process of smelting requires considerable skill. The ore from which iron is obtained in Great Britain is a carbonate of iron, which accompanies the coal formation, and is usually called clay ironstone.

The ore broken into small pieces is roasted, or exposed to a red heat, to drive off the carbonic acid gas, by which process it loses from one third to one fourth of its weight, according to the goodness of the ore. In general three and a fourth tons of raw ore arc reduced by roasting to two and a fourth tons. From this quantity of ore about one ton of cast iron is usually obtained.

The roasted ore is mixed with limestone and coke,^[12. Of late years the air, before it enters the furnace, is heated almost to ignition. In consequence of this improvement raw coal is now used in various furnaces instead of coke. ] and smelted in a blast furnace. The furnace is a kind of cone, from thirty-six to sixty feet in height. It is built of good fire brick, and is double to keep in the heat. Limestone is used as a flux, to separate the clay with which the ore is always contaminated. In general two and a fourth tons of roasted ore require nineteen hundredweight of limestone; or, in round numbers, three tons of raw ore require one ton of limestone. About six tons of coal are required to make one ton of iron. But the coal loses nearly half its weight in coking, so that uncoked coal must go a good deal farther.

The furnace is always kept full, and after being lighted is never extinguished till it requires to be repaired. The air is driven into the furnace from large cylinders by means of a steam engine. The furnace is tapped every twenty-four hours, and the melted iron is allowed to run into sand moulds, and cast into ingots usually called pngs. The scoriae flow out after the iron, and are thrown away. By this process the iron is obtained in the state of cast iron. Of this there are three qualities, distinguished by the names of No. 1, No. 2, and No. 3. Of this No. 1 is the most, and No. 3 the least valuable, while in the state of cast iron. These three qualities are easily distinguished by the scoriae.

The scoriae of No. 1 are uniform in colour and appearance, glassy, and feebly translucent.
[7:6:403]

The scoriae of No. 2 are opaque, heavy, of a yellowish-green colour, exhibiting bands of bluish enamel.

The scoriae of No. 3 are black, vitreous, blebby, and give out the smell of sulphuretted hydrogen gas.

When the cast iron is intended to be used in the state in which it is first obtained, the object of the smelter is to form No. 1, though this is not always in his power. But when the iron is to be converted into bar-iron, the cast iron is always obtained in the state of No. 2. The composition of the scoriae in that case is most commonly two atoms silicate of lime and one atom silicate of alumina; but there is usually present also some silicate of iron and silicate of magnesia.

To convert cast iron into bar-iron three successive processes are requisite. The first of these is called refining. By this process it is converted into No. 3, or white cast iron. Six pigs of cast iron are put at once into the furnace, and covered with coke above and below. They are fused, and kept in that state for twenty-four hours. Much carbonic oxide gas is given out during this process, and burns with a blue flame. It is drawn, cast into a cake, and cooled by water. It is now white and very hard. Its fracture is fibrous, and it is often filled with spherical cavities.

The scoriae from this process are obviously derived from impurities in the cast iron, and from the ashes of the coke. They are black, metallic, often fibrous, and crystallized. A specimen of these scoriae was found composed of one atom phosphate of alumina, and eight and a half atoms silicate of iron. The loss sustained during the process varies from twelve to seventeen per cent. For every ton of cast iron refined, from two to two and a half tons of coke are employed.

The second process, called puddling i was contrived by Mr Cort of Gosport in 1785. It lasts about two hours and a half. The metal of the last process is put into a reverberatory furnace, in which it is arranged round the edges. Heat is applied by the flame of pit-coal, which is made to play upon it. The metal softens; it is stirred, and gradually falls to pieces. The fire is then lowered, and the stirring continued till the metal is reduced to the consistence of sand. In this state much carbonic oxide is given out; and when the evolution of the gas is over, the fire is raised, and the stirring continued. The particles begin gradually to cohere, or to worh heavy as the workmen term it. The operator now collects the iron into balls, and raises the heat to a welding temperature. It is then taken out of the furnace, and either hammered or rolled into bars. During this process the scoriae are squeezed out, and the iron left in a state of purity.

The loss of weight sustained by the iron in this process varies from eight to ten per cent. The scoriae formed are black, very heavy, and sometimes crystallized in the form of pyroxene. Most commonly they consist of scsquisili-cate of iron.

The bars of iron thus formed are called mill bars. The quality is so bad that this iron is scarcely fit for any purpose. To improve it the bars are made to go through another process, called welding. The bars are heated red hot, and cut in pieces by scissors. Four of these bars are placed one above another in a reheating furnace. In half an hour they begin to adhere. They are then drawn out into bars by means of a cylinder. When very good iron is required, as for anchors, this welding process is repeated.

Scoriae appear during this process. They are lamellar and steel gray. In their cavities they contain crystals of pyroxene. They consist of sesquisilicate of iron, with a little sesquisilicate of alumina.

Iron has a grayish colour and the metallic lustre, and when polished has a good deal of brilliancy. Its hardness exceeds that of most metals, and when in the state of steel it may be rendered harder than most bodies. Its specific gravity is 7∙843 after hammering. It is attracted by the magnet, and may be itself converted into a permanent magnet. It is malleable at every temperature, and the malleability increases as the temperature augments. It is very ductile, and may be drawn out into wires finer than a human hair. When drawn out into wire, its strength is one and a half times that of hammered iron. It begins to be elongated, or to lose its shape, when subjected to a force amounting to two thirds of that which is capable of breaking or bursting it. An iron wire 0Ό78 inch in diameter is capable of supporting 449∙34 lbs. avoirdupois without breaking.

When iron is exposed to the air, especially to moist air, it soon tarnishes, and becomes covered with a brownish-red matter, well known by the name of rush It is occasioned by the gradual combination of the iron with oxygen. At a red heat it decomposes water rapidly, hydrogen gas being given out, and the iron converted into an oxide.

I. Iron combines with two doses of oxygen, and forms < two oxides. The protoxide is blackish blue, the peroxide red.

1. The protoxide of iron is formed whenever iron is dissolved in dilute sulphuric or muriatic acid. The solution is light green, and when an alkali is dropt into the liquid, the protoxide of iron falls in the state of light-green flocks, which gradually collect at the bottom of the vessel, and assume a black colour. Its tendency to absorb oxygen is so great that we cannot collect it so as to allow it to retain its colour. When a current of hydrogen gas is passed through peroxide of iron heated in a glass tube considerably under redness, it is gradually converted into protoxide. In this state it has a blackish-blue colour, appearing by reflected light almost black. In the open air it burns with great splendour, and is converted into peroxide. It is composed of
[table]

so that the atomic weight of iron is 3∙5, and that of protoxide of iron 4*5.

2. Peroxide of iron is usually obtained by dissolving iron in nitric acid, evaporating the solution to dryness, and exposing the dry residue to a heat gradually raised to redness. It is a fine red powder, destitute of taste and smell, insoluble in water, but soluble in acids, especially the muriatic. After exposure to a red heat, it loses much of its easy solubility in acids. It is composed of
[table]

so that its atomic weight is 5. ρ rp

Two hydrates of peroxide of iron^⅛ecur native. 1. Dihydrate, a red-coloured fibrous mid^rl* found in nodules in the rocks in the neighbourhood or Gourock, near Greenock, in Scotland. It is composed of ⅛
[table]

The red fibrous mineral us<ally called hematite is a compound of a *∙ Ä ~tK
[table]

It is therefore a simple hydrate of the peroxide of iron.

Rust consists chiefly of hydrated peroxide of iron, but [7:6:404] it is mixed not unfrequently with a quantity of carbonate of iron.

3. These two oxides have the property of mixing or combining in various proportions, and forming substances which have been considered as constituting peculiar oxides of iron.

When bars of iron are heated to whiteness and hammered, scales are driven off, known in this country by the name of smithy aslιes. These scales are composed of two atoms protoxide and one atom peroxide of iron.

When bars of iron are heated and allowed to cool in the open air, the outermost scales contain more peroxide than the innermost; the inner layer is a compound of three atoms protoxide and one atom peroxide, while the outermost is a compound of one atom protoxide and one atom peroxide.

By the combustion of iron wire in oxygen gas, there is sometimes formed a compound of ’ one atom protoxide and two atoms peroxide. To this compound Berzelius has given the name of oxidum ferrosoferricum.

II. Chlorine, like oxygen, unites to iron in two proportions.

1. Chloride of iron may be formed by dissolving iron in muriatic acid, evaporating the solution to dryness, and exposing the dry mass to a red heat in such a way as to exclude the action of air on it. It has a gray but variegated colour, and a metallic splendour. Its texture is lamellated. When heated to redness it melts, but is not volatilized. It is imperfectly soluble in water, and the solution yields green crystals. It is a compound of
[table]

2. The sesquichloride of iron may be obtained by burning iron wire in chlorine gas, or by evaporating a solution of red oxide of iron in muriatic acid to dryness, and heating it in a tube with a narrow orifice. It is a substance of a bright-brown colour, with a lustre approaching that of ore from Elba. It may be volatilized by a moderate heat, and forms minute brilliant crystals. It is completely soluble in water. It is composed of
[table]

III. When iron wire is heated to redness in a glass tube, and dry bromine vapour passed over it, the wire becomes incandescent, and fuses without the evolution of any gas. The bromide thus formed has a yellow colour and a lamellar structure. It dissolves readily in water without communicating colour to that liquid, and the solution is precipitated light yellow by nitrate of silver. This bromide is composed of
[table]

IV. When iron is heated in contact with the vapour of iodine, an iodide is formed, which has a brown colour, and fuses when exposed to a red heat. It dissolves in water, communicating a light-green colour. It is doubtless a compound of
[table]

V. It is probable that iron and hydrogen are capable of combining at a certain temperature, but nothing is known respecting the properties of this compound.

VI. Iron combines with carbon, and forms the important compounds known by the names of cast iron and steel.

There are three varieties of cast iron commonly distinguished in commerce; namely, black cast iron, usually called No. 1; mottled cast iron, or No. 2; and white cast iron.

1. Black cast iron is the softest of the three. Its specific gravity varies from 6∙90102 to 6 ’ 836. It is imperfectly malleable, and admits of being easily turned on the lathe and filed down. It melts at a comparatively low heat. Its texture is granular. It is much used in this country for the numerous purposes to which cast iron is applied.

2. Gray or mottled iron is so called from the inequality of the colour. Its specific gravity is 7∙0683. It is harder than the black variety, but soft enough to be cut, bored, and turned on the lathe. It is much used. For many purposes it is found expedient to mix No. 1 and No. 2, and fuse them together. Artillery is usually made of mottled cast iron.

3. White cast iron has a white colour like silver. Its texture is fibrous or crystalline, and its specific gravity 7 ’ 6849. It is too hard to be filed, bored, or bent, and it is very apt to break when suddenly heated or cooled.

Black cast iron seems to be a compound of
[table]

While white cast iron is composed of
[table]

including in the carbon a little silicon, which is variable in quantity. Mottled cast iron is intermediate between the white and black. It has not yet been subjected to analysis.

Steel is a compound of iron of the utmost consequence, because it is from it that all the cutting instruments and files are made. The iron which answers best for being converted in to steel is that made at Dannemora, in Sweden. The Russian iron, known by the name of old sable, is also capable of being converted into good steel.

The furnace in which iron is converted into steel has the form of a large oven or arch, terminating in a vent at the top. The floor of this oven is flat and level. Immediately under it there is a large arched fire-place with grates, which runs quite across from one side to the other, so as to have two doors for putting in the fuel from the outside of the building. In the oven there are two large and long cases or boxes built of good fire-stone, and in these boxes the bars of iron are regularly stratified with charcoal powder, ten or twelve tons of iron being put in at once, and the box is covered at the top with a bed of sand. The heat is kept up, so that the boxes and all their contents are kept red hot for eight or ten days. A bar is then drawn out and examined, and if it be found sufficiently converted into steel, the fire is drawn and the oven allowed to cool. This process is called cementation.

The bars of steel formed in this way are raised in many places into small blisters, by a gas evolved in the inside of the bar. On this account the steel made in this way is usually called blistered steel. Its texture is not quite equable, but it is rendered so by fusing it in a crucible, and then casting it into bars. Thus treated, it is called cast steel. When steel is to be cast it is made by cementation in the usual way, only the process is carried somewhat farther, so as to give the steel a whiter colour. It is then broken into small pieces, and put into a crucible of good fire-clay, after which the mouth of the crucible is [7:6:405] filled up with vitrifiable sand, to prevent the steel from being oxydized by the action of the air. The crucible is exposed for five or six hours to the most intense heat that can be raised, by which the steel is brought into a state of fusion. It is then cast into parallelopipeds about a foot and a half in length. To fuse a ton of steel about twenty tons of coals are expended.

The specific gravity of good blistered steel is 7∙823; but by heating it to redness, and then plunging it into cold water, the specific gravity is reduced to 7∙747. The colour of steel is whiter than that of iron. Its texture is granular, its fracture is whitish gray, and much smoother than the fracture of iron. It is much harder and more rigid than iron, nor can it be so much softened by heat without losing its tenacity, and flying to pieces under the hammer. It requires more attention to forge it than to forge iron; yet it is by its toughness, and capability of being drawn out into bars, that good steel is distinguished from bad. Steel is more readily broken by bending it than iron. If it be heated to redness, and then suddenly plunged into cold water, it becomes exceedingly hard, so as to be able to cut or make an impression on most other bodies; but when iron is treated in the same way, its hardness is not in the least increased. When a drop of nitric acid is let fall upon a smooth surface of steel, and allowed to remain on it for a few minutes, and then washed off with water, it leaves a black spot; whereas the spot left by nitric acid on iron is greenish white. Steel is not so easily converted into a magnet as iron; but when once converted it retains its magnetic virtue, whereas iron loses it immediately when the exciting cause is withdrawn. Steel possesses great elasticity, and the elasticity appears to be the same in all states of temper.

Steel, like cast iron, is a compound of iron and carbon, but it contains much less carbon than even white cast iron. Cast steel would appear to be a compound of
[table]

The constitution of blistered steel does not differ much from this.

VII. When iron filings and boracic acid are fused in a covered crucible, a ductile mass of a silver colour is obtained, which is probably a boruret of iron. A silicet of iron may be obtained by a similar process, substituting silica for boracic acid. The properties of this silicet approach very nearly those of the boruret.

VIII. There exists a strong affinity between iron and sulphur. Five sulphurets of iron are known, and others may be discovered hereafter.

1. Sulphuret of iron may be formed by passing hydrogen gas over pyrites in powder, and heated to redness in a glass tube. One half of the sulphur is disengaged, and there remains a compound of
[table]

The same sulphuret is obtained when iron is heated to whiteness, surrounded by sulphur vapour. The union is accompanied by the fusion of the sulphuret, and a good deal of heat is evolved. Its colour is that of bronze or black when in powder, and it dissolves in sulphuric or muriatic acid with the evolution of much sulphuretted hydrogen gas. It may be obtained also when iron pyrites is distilled at a red heat; one half of the sulphur flies off and leaves the sulphuret.

2. Sesquisulphuret of iron may be formed by passing a current of dry sulphuretted hydrogen gas over peroxide of iron in a glass or porcelain tube heated to the temperature of 212°. The gas must be continued till all evolution of water is at an end. The sesquisulphuret formed has the same form as the peroxide had. It has a gray colour, with a slight shade of yellow, and acquires lustre under the burnisher. It is not altered by exposure to the air. When distilled, sulphur is given out and common sulphuret remains. When treated with acids, sulphuretted hydrogen gas is evolved, iron is dissolved, and a quantity of bisulphurct of iron remains undissolved. Its constituents are,
[table]

3. Bisulphuret of iron is found native in abundance, and is well known by the name of pyrites or iron pyrites. It has a yellow colour, and the metallic lustre. It is brittle, and sufficiently hard to strike fire with steel. Its specific gravity is about 4 ’ 5. It usually crystallizes in striated cubes. When heated it is decomposed. In the open air the sulphur takes fire. In close vessels filled with charcoal, part of the sulphur is volatilized, and a black matter remains, which is common sulphuret. It is a compound of
[table]

4. Disulphuretof iron may be obtained by passing a current of dry hydrogen gas over anhydrous sulphate of iron heated in a glass tube. Sulphurous acid and water pass over first, and at last sulphuretted hydrogen gas. The disulphuret is a dark-gray agglutinated powder, strongly attracted by the magnet. It dissolves in muriatic acid with the evolution of sulphuretted hydrogen gas. Its constituents are,
[table]

5. Tetrasulphuret of iron may be obtained by exposing anhydrous disulphated peroxide of iron to a current of dry hydrogen gas while heated in a glass tube. Sulphurous acid and sulphuretted hydrogen gas are evolved. The sulphuret obtained resembles metallic iron. It is powerfully acted on by the magnet, and is semiductile; but it dissolves in muriatic acid with the evolution of sulphuretted hydrogen gas. It is composed of
[table]

IX. When a mixture of selenium and iron filings is heated, a combination takes place without any appearance of combustion. But if th^e selenium be put into the bottom of a glass tube, and iron filings above it, and a sufficient heat be applied to volatilize the selenium, the iron filings absorb this vapour and become red hot, and this ignition continues as long as any selenium is absorbed. The seleniet thus formed has the metallic appearance, and a gray colour, with a shade of yellow. It does not melt, but becomes agglutinated together into a coherent mass. It dissolves readily in muriatic acid, while selenietted hydrogen gas is disengaged.

X. Iron combines with phosphorus in various proportions.

1. A phosphuret of iron may be formed by fusing together sixteen parts of phosphoric glass, sixteen parts of iron, and half a part of charcoal powder. It is magnetic, very brittle, and appears white when broken.' ∣ When exposed[7:6:406] to a strong heat it melts, and the phosphorus is dissipated. It is probably a diphosphuret, composed of
[table]

What is called cold short iron, owes its brittleness to the presence of a quantity of phosphuret of iron.

2. When a current of dry hydrogen gas is passed over phosphate of iron heated to redness in a glass tube, both constituents are deprived of their oxygen, and a phosphuret remains, composed of
[table]

3. When phosphuretted hydrogen gas is passed very slowly over iron pyrites at a high temperature, a phophu-ret is obtained, composed of
[table]

XI. When a hundred parts of iron filings and two hundred parts of arsenic are heated to redness, an arseniet is obtained, which is white, very brittle, and easily pulverized. It is composed of
[table]

XII. Iron combines with antimony by fusion, and forms a brittle, hard, white-coloured alloy, the specific gravity of which is less than intermediate. The magnetic quality of iron is much more diminished by being alloyed with antimony than with most other metals.

XIII. When oxides of iron and of chromium are mixed together, and strongly heated in a covered crucible lined with charcoal, they are reduced, and melt together into an alloy. Its texture is crystalline, and it is whiter than platinum.

Sect. II.— Of Manganese.

Manganese is found usually in the state of a gray or black oxide, having often considerable lustre, and giving out the eleventh of’ its weight of oxygen gas when exposed to a red heat. It is seldom pure, being almost always contaminated with oxide of iron. To purify it, the easiest process is to roast the impure manganese ore, previously reduced to a fine powder, with a quantity of charcoal powder. This brings the manganese to the state of protoxide. It is now treated with a sufficient quantity of dilute sulphuric acid, to dissolve almost, but not the whole of the manganese, and this acid is mixed with muriatic acid. The solution takes place with the evolution of much heat. The iron is peroxydized and thrown down by the excess of protoxide of manganese present. The liquid, on standing, becomes transparent and colourless. When sufficiently concentrated, abundance of crystals of sulphate of manganese are obtained, contaminated merely with a little chloride or bichloride of manganese. Dissolve these crystals in water, and add to the solution carbonate of soda. A copious white precipitate falls, which is pure carbonate of manganese. When this carbonate is mixed with charcoal and exposed to an intense heat in a covered crucible, it is reduced to the state of metallic manganese.

Manganese thus obtained is rather whiter than cast iron. Its texture is granular, and it may be reduced to powder by pounding in a mortar. Its specific gravity is 8 ’ 013. It is not attracted by the magnet. It gradually absorbs oxygen from the atmosphere, and decomposes water; but when alloyed with iron it loses that property, and may be kept without alteration.

I. Manganese has a strong affinity for oxygen. It is capable of forming at least four oxides, and the existence of a fifth, containing less oxygen than any of the rest, is far from improbable.

1. The protoxide constitutes the base of almost all the salts of manganese. It may be obtained by passing a current of dry hydrogen gas over any of the other oxides of manganese, heated in a glass tube, but not to redness. It is a light-green powder, which becomes yellow, and then brown, when exposed to the air. It is composed of
[table]

so that its composition and atomic weight exactly agree with those of protoxide of iron.

2. The easiest way of forming sesquioxidc of manganese is to dissolve carbonate of manganese in nitric acid, evaporate the solution to dryness, and raise the dry mass by degrees to an incipient red heat. It is a black powder, having considerable lustre. It is tasteless and insoluble in water, but dissolves in sulphuric and muriatic acids, and the solution is red. It occurs native both in the hydrous and anhydrous state. Its constituents are,
[table]

so that it corresponds in its constitution with peroxide of iron.

3. Binoxide of manganese exists native; its colour is: iron black, its lustre metallic, and its texture fibrous. It is soft, rather sectile, and has a specific gravity varying from 4∙94 to 4∙819. It constitutes the most important of all the ores of manganese, from the property which it has of giving out oxygen when heated. When a current of chlorine gas is passed through water in which carbonate of manganese is suspended, this oxide is formed. Carbonic acid is disengaged, part of the manganese is dissolved, and part is converted into hydrated binoxide. By digesting the brown residue in dilute nitric or acetic acid, any unaltered carbonate is dissolved, and the binoxide remains pure. It is a very bulky and light-brown powder, which retains its bulk when dried on the water bath, and adheres strongly to those bodies with which it comes in contact. In this state it is a compound of
[table]

The binoxide itself is a compound of
[table]

4. Scheele first discovered that when binoxide of manganese is strongly heated with potash or saltpetre, and the mixture dissolved in water, a fine red solution is obtained, which, having the property of changing its colour, he called chameleon mineral. From this liquid a salt may be obtained, composed of an acid having manganese for its base, and of potash. To the acid the name of manganesie has been given, and the salt is called manganate of potash. The acid may be obtained in the following way: Mix two parts of nitrate of barytes and one part of binoxide of manganese, and expose the mixture in a crucible to a strong red heat. By this process a light-green mass is obtained, which [7:6:407] is considered as a submanganate of barytes. Reduce this matter to a very fine powder, and mix it with thirty times its weight of water. Through this mixture pass a current of carbonic acid gas till the liquid assumes a violet colour, and till the sediment at the bottom has changed from green to brown. Then boil the liquid for a quarter of an hour, and add a drop or two of sulphuric acid to throw down any barytes that may still remain in solution, taking care not to add any excess. The liquid now consists of a solution of manganesic acid in water. By evaporation to dryness in a gentle heat the acid may be obtained in a solid state.

Manganesic acid thus obtained is in very small needles. It is a hydrate, composed of two atoms manganesic acid and one atom water. This water is essential to the existence of the acid. When we attempt to drive it off, the acid is decomposed. Manganesic acid has a dark carmine-red colour, and is destitute of smell. It has a disagreeable taste, being a kind of mixture of bitter and astringent. It is heavier than water. It is capable of being converted into vapour by heat, and may be again condensed without decomposition. When it is mixed with sulphuric acid the temperature rises to at least 226°, and a violet vapour appears, which is said to be a compound of manganesic and sulphuric acids. Manganesic acid is but little soluble in water. It is gradually decomposed by exposure to light, and likewise by heat. The aqueous solution soon loses its colour when kept boiling hot. Oxygen, chlorine, and azote, have no action on it whatever. Iodine decomposes it in consequence of its conversion into hydriodic acid. Hydrogen, phosphorus, sulphur, and charcoal, decompose it. Most of the metals have the same effect. It is decomposed by zinc, iron, bismuth, copper, antimony, lead, mercury, and silver, in a longer or shorter time. Sulphuric acid, nitric acid, phosphoric acid, arsenic acid, chromic acid, boracic acid, and carbonic acid, have no action on it. Sulphurous acid and smoking nitric acid destroy it immediately without throwing down any manganese. It is decomposed also by the hydracids. This acid, from the best analysis of it hitherto made, is a compound of
[table]

Its atomic weight is six, and it agrees in its constitution with phosphoric, arsenic, antimonic, and chromic acids.

. 5. When sesquioxide or binoxide of manganese is exposed to a strong red heat, it gives out oxygen, and varies in colour according to the state of the oxide subjected to heat. The usual colour is a brownish red or a brownish black. The oxide formed by this process is usually called red oxide of manganese by chemists. It is a compound of
[table]

or we may represent its constitution as follows, which is more convenient for chemical analysis:
[table]

This oxide occurs native, and it is formed whenever any oxide of manganese is strongly heated in an open vessel. Arfvedson, who first investigated the nature of this compound oxide, gave it the name of oxydum manganoso∙ rnangαnicurn.

6. There is an ore of manganese found in Warwickshire, to which Mr Phillips, who first examined it, has given the name of varvicite. It is black, has the metallic lustre, a foliated texture, and is very soft. This last property readily distinguishes it from sesquioxide or bromide, with which, in other respects, it might be confounded. It is a compound of
[table]

or (which is more convenient) we may represent it as consisting of
[table]

Like red oxide, it is rather a compound of two oxides than a peculiar oxide.

II. Two combinations only of chlorine and manganese are at present known.

1. The protochloride may be obtained by dissolving carbonate of manganese in muriatic acid, evaporating the solution to dryness, and exposing the residual salt to a red heat in a glass tube with a narrow orifice. It is a substance having a delicate light-pink colour and a lamellar texture. It melts at a red heat without alteration in close vessels; but in the open air it is decomposed, muriatic acid being given out, and oxide of manganese remaining. In the open air it speedily deliquesces. It is a compound of
[table]

2. Perchloride of manganese may be formed in the following manner: Form common green chameleon mineral, and change it to red chameleon by adding sulphuric acid. When the solution is evaporated, a mixture of sulphate and manganate of potash is obtained. Mix this matter with concentrated sulphuric acid, and project into it common salt by small fragments at a time as long as coloured vapours continue to arise. The perchloride of manganese is given out in the form of a green vapour, which being made to pass through a glass tube surrounded by a mixture of snow and salt, condenses into a greenish-brown liquid. It retains its elastic form at the ordinary temperature of the atmosphere, and is so heavy that it may be poured from one vessel to another. When it comes in contact with water it is immediately decomposed into muriatic acid and manganesic acid. Hence its constituents are obviously
[table]

The bromides and iodides of manganese are still unknown.

III. When two parts of chameleon mineral, one part of fluor spar in powder, and a sufficient quantity of concentrated sulphuric acid to convert the whole into a paste, are mixed in a platinum retort, and the beak of the retort is plunged into a platinum crucible containing water, a greenish-yellow gas comes over, which is rapidly absorbed by the water, and tinges it of a beautiful purple. The solution consists of a mixture of fluoric acid and manganesic acid. Hence it is probable that the gas is a perfluoride, composed of
[table]

IV. Manganese is capable of combining with carbon.
[7:6:408]

This carburet is formed occasionally during the melting of cast iron, and in Staffordshire is known by the name of heesh. It occurs in small cavities in the cast iron, and seems to be the result of crystallizing during the cooling of the mass. It is in thin scales, having the lustre and appearance of steel, but very soft and brittle. Its specific gravity, when purified from iron, is 2∙982.

, V. Only one sulphuret of manganese has been hitherto discovered. It exists native at Nagyag, in Transylvania, and is a black opaque substance with a dark-green streak. Its specific gravity is about four, and it is said to occur crystallized in cubes. It may be formed artificially by mixing anhydrous sulphate of manganese with τ 1 c ∙th of its weight of charcoal powder, and exposing it to an incipient white heat in a covered crucible, or by passing a current of sulphuretted hydrogen gas over protoxide of manganese heated to redness in a porcelain or glass tube. When dissolved in acids, sulphuretted hydrogen gas is evolved, and a salt of protoxide of manganese formed. Hence it is obviously a compound of
[table]

The native sulphuret is a compound of seventeen atoms manganese and eighteen atoms sulphur. The probability is that a bisulphuret of manganese exists, and that the native sulphuret is a compound of sixteen atoms sulphuret and one atom bisulphuret.

When a current of hydrogen gas is passed through anhydrous sulphate of manganese heated to redness in a glass tube, one half of the sulphur is carried off, and one half of the manganese reduced to the metallic state; so that the light-green powder formed is a compound or mixture of one atom sulphuret of manganese, and one atom protoxide of manganese.

λVhen carbonate of manganese is heated with sulphur, the manganese is converted chiefly into sulphuret; but there is formed at the same time a little sulphate, which renders the sulphuret impure.

Sect. III.— Of Nickel.

Nickel is obtained chiefly from an impure metallic alloy prepared in Germany, and known by the name of speiss. Besides nickel, it contains arsenic, iron, copper, cobalt, bismuth, and probably other substances. If we reduce this speiss to a coarse powder, and digest it in dilute sulphuric acid, mixed with as much nitric acid as occasions a brisk effervescence, we obtain a fine green-coloured liquid, which yields, when concentrated, abundance of fine crystals of sulphate of nickel. Dissolve these in water, pass a current of sulphuretted hydrogen gas through the solution, and then crystallize a second time. Redissolve in water, and throw down the oxide of nickel by an alkali or alkaline carbonate. Convert the oxide of nickel thus obtained, and which is still contaminated with a little cobalt, into oxalate, and dissolve the oxalate in dilute ammonia. Leave the solution exposed to the air, and the nickel will be deposited in the state of ammonia-oxalate, while the cobalt remains in solution, giving it a red colour. When this ammonia-oxalate of nickel is strongly heated in a covered crucible, it is reduced to the metallic state.

Nickel, when pure, has a white colour, like silver, and it leaves a white trace when rubbed upon the polished surface of a hard stone. It is rather softer than iron. Its specific gravity, after being strongly hammered, is 8 ’ 932. After fusion it is 8∙380. It is malleable, both hot and cold, and may be easily hammered out into thin plates. It is attracted by the magnet, and, like steel, may be converted into a permanent magnet. Its magnetic energy is to that of iron nearly as three to five. The preparations of this metal possess poisonous qualities.

I. Nickel combines readily with oxygen. It forms two oxides; the protoxide is ash-gray i and the peroxide l>lack.

1. Nickel cannot be converted into protoxide by exposure to heat, however long continued; but we obtain it easily by dissolving nickel in nitric acid, and throwing the oxide down by potash, and, after washing the precipitate, drying it, and heating it to redness. Its colour is ash-gray; it is not magnetic, and dissolves very readily in acids, but is insoluble in the caustic fixed alkalies. Caustic ammonia dissolves it, and the solution has a fine sky-blue colour, and is precipitated by caustic potash, soda, barytes, strontian, or lime. It is a compound of
[table]

2. The peroxide of nickel may be obtained by passing a current of chlorine gas through water holding protoxide of nickel suspended in it. A portion is dissolved, and the rest assumes a black colour. Peroxide of nickel is soluble in ammonia, but the solution is accompanied with effervescence, owing to the decomposition of part of the ammonia, from the combination of its hydrogen with part of the oxygen of the peroxide. This oxide is composedOf
[table]

When protohydrate of nickel is treated with deutoxide of hydrogen, a dark-green matter is formed, which Thénard considers as containing more oxygen than the black oxide.

II. When nick-el is left in contact with chlorine gas, an olive-coloured compound is obtained, which is a chloride of nickel. The same chloride may be formed by dissolving protoxide of nickel in muriatic acid, evaporating the solution to dryness, and subliming the residual salt.

III. When nickel and iodine are heated in a glass tube, a brown fusible mass is obtained, composed of
[table]

IV. Nickel combines with carbon, and forms a carburet. Indeed, as usually prepared, it is never destitute of carbon. It is always obtained when oxide of nickel and charcoal powder are heated together in a covered crucible. The quantity of carbon present is not great, but it has not been determined by analysis.

V. We are acquainted with two combinations of nickel and sulphur.

1. Sulphuret of nickel exists native, and is known by the name of haarkies. It is brittle, and before the blowpipe easily melts. It dissolves in nitromuriatic acid, without any other residue than a little sulphur. It is composed of
[table]

This sulphuret may be formed artificially by passing a current of sulphuretted hydrogen gas over oxide of nickel heated to redness in a glass tube. When thus formed it has a dark-gray colour, and is not attracted by the magnet.

2. When a current of dry hydrogen gas is passed over anhydrous sulphate of nickel heated in a glass tube to incipient redness, one half of the sulphur passes off, and the whole of the nickel is reduced to the metallic state. The disulphuret formed has a pale-yellow colour, and when [7:6:409] burnished assumes the metallic lustre. It is brittle, and is attracted rather strongly by the magnet. It is a compound of
[table]

VI. Phosphuret of nickel is white, and when broken exhibits the appearance of very slender prisms collected together. When heated, the phosphorus burns, and the nickel is oxydized. It seems to be a compound of three atoms nickel and one atom phosphorus.

VII. Arseniet of nickel occurs native, and is known by the name of copper-nicltel i from its colour. Its colour is copper-red, it is brittle, not magnetic, and has a specific gravity of 7∙29. It is composed of
[table]

Sect. IV— Of Cobalt.

Cobalt is obtained chiefly from a white metallic ore usually crystallized in cubes or dodecahedrons, very heavy, and known by the name of cobalt-glance. It is chiefly a compound of cobalt, arsenic, and sulphur. The cobalt may be separated from it by the following process: Reduce the ore to powder, and roast it in a moderate heat to drive off a portion of the arsenic and sulphur. Then dissolve it in nitric acid, and evaporate the solution to dryness, and digest the dry mass in water. A quantity of arseniate of iron remains undissolved. Should the ore contain no iron, a little of that metal should be added to the nitric acid solution. Filter off the aqueous solution, and pour into it a quantity of binoxalate of potash previously dissolved in water. In a few hours the whole cobalt precipitates in the state of oxalate. Digest this oxalate in ammonia, which will dissolve it, and set the solution aside in an open vessel till the excess of ammonia has had time to be dissipated. The oxalate of nickel, should any be present, will precipitate, and the oxalate of cobalt in a state of purity will remain in solution. Evaporate to dryness, and expose the oxalate of cobalt to a red heat in a covered vessel. The cobalt is reduced to the metallic state, and by exposure to a violent heat, while covered with a little borax, it may be fused into a mass.

. Cobalt has a gray colour, with a shade of red, and is by no means brilliant. Its texture is usually granular. It is rather soft. Its specific gravity is 8∙7. It is brittle, and easily reduced to powder. Like iron, it is attracted by the magnet, and it may be converted into a magnet, which is not quite so powerful as a magnet of iron. It dissolves very slowly in dilute sulphuric and muriatic acids, with the evolution of hydrogen gas; but nitric acid dissolves it readily. It may be kept either in the open air or under water without undergoing any sensible alteration.

I. Cobalt, when kept red hot in the open air, is gradually oxydized. In a violent heat it takes fire and burns with a red flame. Like iron and nickel, it combines with two proportions of oxygen, and constitutes two distinct oxides.

1. Protoxide of cobalt may be obtained by dissolving the metal in nitric acid, and precipitating by potash. The precipitate has a blue colour, but when dried in the open air gradually becomes greenish. When heated to a cherry red, however, it again recovers its original blue colour. It dissolves in acids without effervescence. The solution in muriatic acid, when concentrated, is green, but when diluted red. The sulphuric and nitric acid solutions are always red. It gives a fine blue colour to glass, and is used for paintina blue on stoneware. It is soluble in caustic and carbonated ammonia, and the solution has a brownish-red colour, and is not precipitated by caustic potash. It dissolves in caustic potash, and the solution has a blue colour. It is thrown down unaltered· by dilution with water. It is composed of
[table]

2. When the protoxide of cobalt, newly precipitated from an acid, is dried in the open air, it assumes a flea-brown colour, which gradually deepens, till at last it becomes black. In this state it constitutes peroxide of cobalt. It may be formed also by passing a current of chlorine gas through water in which the protoxide is suspended, or by agitating the protoxide in a saturated solution of chloride of lime. It dissolves in none of the acids except the muriatic, and during its solution in that acid much chlorine gas is evolved. Its specific gravity is 5∙322. It is a compound of
[table]

II. Cobalt burns when gently heated in chlorine gas. When protoxide of cobalt is dissolved in muriatic acid, and the solution evaporated to dryness, a red mass remains. When this matter is heated in a retort, chloride of cobalt sublimes in the form of a blue-coloured voluminous snow. It gradually absorbs moisture from the atmosphere. It is composed of
[table]

It is the solution of this chloride which constitutes the sympathetic ink of Hellot. Letters made with it on paper have a red colour while moist, but become blue when the paper is dried.

Bromide and iodide of cobalt are still unknown.

III. Sulphur combines with cobalt in three proportions, forming sulphuret, sesquisulphuret, and bisulpliuret i of cobalt.

1. When sulphate of cobalt is heated to whiteness in a charcoal crucible, it is converted into sulphuret. It is formed also when a salt of cobalt is mixed with a solution of a sulphohydrate. It is a yellowish-white substance, having the metallic lustre, and is attracted by the magnet. It is a compound of
[table]

2. When a current of dry hydrogen gas is passed over anhydrous sulphate of cobalt heated to redness in a glass tube, half the oxide is reduced to the metallic state, and half the sulphur expelled. The residue is a dark-gray mass. When heated, a little sulphuretted hydrogen gas is disengaged. When it is heated to redness in a glass tube, and a current of dry sulphuretted hydrogen gas passed over it, water is given off’, and a sesquisulphuret remains. It is a dark-aray matter, composed of
[table]

3. When sesquisulphuret of cobalt is digested in muriatic acid, one fourth of the cobalt is dissolved, and a bisulphuret remains. It is a black powder, destitute of lustre. It is not acted on by alkalies, nor by acids, with [7:6:410] the exception of the nitric and aqua regia. At a red heat it gives out sulphur, and is converted into sesquisulphuret. It is a compound of
[table]

IV. Cobalt readily absorbs selenium when assisted by heat. When the compound is heated to redness it melts, gives out its excess of selenium, and forms a gray-coloured mass, having the metallic lustre and a foliated fracture.

V. Phosphuret of cobalt is white and brittle, and when exposed to the air soon loses its metallic lustre. The phosphorus is separated by heat, and the cobalt at the same time oxydized. This phosphuret is much more fusible than pure cobalt.

VI. Arsenic and cobalt have a strong affinity for each other. Almost all the ores of cobalt contain arsenic. It is found native, combined with arsenic in three proportions, forming a sesquiarseniet, binarseniet, and terarseniet of cobalt.

FOURTH FAMILY. EASILY FUSIBLE BASES.

Of the eight metals belonging to this family, five were known to the ancients in the metallic state. Zinc in the metallic state was unknown to them; but they were acquainted with its oxide, and with the alloy which it forms with copper. Bismuth was unknown in Germany before the year 1500, while cadmium was discovered by Stromeyer about the year 1817.

Sect. I.— Of Zinc.

Zinc is found in the earth either in the state of an oxide combined with carbonic acid or silica, when it is called calamine, or in the metallic state united with sulphur, when it is distinguished by the name of blende. Metallic zinc is usually obtained by heating a mixture of calamine and charcoal in earthen vessels shut above, and having a pipe issuing from their bottom, and terminating in a bucket of water. The zinc is reduced and volatilized. It enters the tube, and drops in small pieces into the water. It is then cast into ingots.

Zinc has a white colour, with a shade of blue, and is composed of plates adhering together. It is rather soft. Its specific gravity after fusion is 6∙896. By hammering it may be made as high as 7∙1908. At the common temperature of the air it is scarcely malleable, yet it is too tough to be reduced to powder by pounding in a mortar. When heated a little above 212° it is very malleable, and may be rolled out into thin plates, which retain their flexibility when cold. At the temperature of 400° it is so brittle that it may easily be pounded in a mortar. It melts at about 680°, or before it is quite red hot. It is very little altered by exposure to the air. When kept under water it is said to become black, and to occasion the evolution of hydrogen gas.

I. So far as is known at present, zinc unites with only one proportion of oxygen. The oxide is easily formed by heating zinc to redness in the open air. It takes fire and burns with a brilliant white flame, and emits a vast quantity of white flakes somewhat like cobwebs. These constitute oxide of zinc. This oxide may be obtained also by dissolving zinc in sulphuric acid, and filtering and crystallizing the solution. The crystals are to be dissolved in boiling water, and the solution mixed with carbonate of soda. A white precipitate falls, which, when washed, dried, and∙ignited, constitutes pure oxide of zinc.

Oxide of zinc is snow-white. When heated it assumes a yellow colour, but becomes again white when allowed to cool. It is tasteless, and insoluble in water; but it dis solves readily in acids, and the solution is colourless. It dissolves also in concentrated caustic ammonia, but is partly precipitated again when the solution is diluted with water. Barytes or lime water also occasions a precipitate when poured into the same solution. The affinity between oxide of zinc and alumina is considerable. When a solution of oxide of zinc in ammonia, and of alumina in caustic potash, are mixed together, the alumina and oxide of zinc are precipitated in combination. The precipitate is again dissolved by an excess of either of the alkalies. This oxide is composed of
[table]

II. Zinc takes fire in chlorine gas, and forms a chloride. When zinc is dissolved in muriatic acid, the solution evaporated to dryness, and the dry mass heated to redness in a narrow glass tube shut at one end, chloride of zinc is obtained. It is a white solid, which melts at a red heat without subliming. When exposed to the air it soon deliquesces. Its constituents are,
[table]

Bromide of zinc has not been examined.

III. Zinc readily combines with iodine by heat. The iodide is white; it is volatile, and crystallizes in four-sided prisms. It deliquesces in the air, and is very soluble in water. The solution is colourless, and does not crystallize. Iodide of zinc is a compound of
[table]

IV. Sulphuret of zinc exists native, and is distinguished by the name of blende. When free from iron it has a light-yellow colour, is translucent, and has the diamond lustre. Its specific gravity is about four. It dissolves with difficulty in muriatic acid, giving out sulphuretted hydrogen gas. Aqua regia dissolves it easily. It melts when exposed to a high temperature. It is composed of
[table]

V. When red-hot zinc is brought in contact with the vapour of selenium, an explosion takes place, and a yellow powder is formed, which is a seleniet of zinc. This powder dissolves in nitric acid with the evolution of nitrous gas. The zinc is oxydized and dissolved, while the selenium separates in the form of a red pow der.

VI. Phosphuret of zinc is of a white colour, with the metallic lustre, but resembles lead more than zinc.

VII. Arseniet of zinc may be formed by fusing the two metals together. It is very brittle, and is usually a compound of
[table]

Sect. II.— Of Cadmium.

This metal exists pretty commonly associated with the ores of zinc. The brownish powder which collects on the roofs of the chambers in which zinc is smelted contains about ten per cent, of cadmium. From this it may be extracted by the following simple process. Digest the matter in dilute sulphuric acid till every thing soluble be [7:6:411] taken up. Into the filtered solution put a polished bar of zinc. The cadmium is thrown down in the metallic state. It may be washed, dried, and fused.

Cadmium has a white colour, with a shade of bluish gray, and approaches nearest to tin in its appearance. It is very malleable, and may be rolled out into thin flexible plates, which have no elasticity, but retain any form given them. Its specific gravity after fusion is 8∙6040. By hammering it may be made as high as 8∙6944. It is very fusible, melting before it becomes red hot. It is also volatile, being converted into vapour by a temperature not much higher than that of boiling mercury. It is not altered by exposure to the air.

I. Cadmium, like zinc, unites with only one proportion of oxygen. When heated to redness in the open air it burns, and is converted into a brownish-yellow powder, which is the oxide. The easiest mode of obtaining this oxide is to dissolve cadmium in dilute sulphuric, muriatic, or even nitric acid, and precipitating the solution, which is colourless, with an alkali. The precipitate, when washed, dried, and ignited, is pure oxide of cadmium. This oxide has a yellow colour, is fixed in the fire, and does not melt in a white heat. It is insoluble in the fixed caustic alkalies, but dissolves readily in ammonia. It is insoluble in carbonate of ammonia, which distinguishes it from oxide of zinc. When sulphuretted hydrogen gas is passed through its solution a fine yellow precipitate falls, which was at first taken for orpiment. The specific gravity of oxide of cadmium is 8∙183. It is a compound of
[table]

This oxide saturates the different acids, and forms with them neutral salts.

II. When cadmium is dissolved in muriatic acid, and the solution evaporated, small transparent rectangular crystals are obtained. When these crystals are heated, water is driven off, and a transparent, foliated, crystallized mass, having a pearly lustre, remains, which is a chloride of cadmium. When exposed to the air it falls down in the state of a white powder. When strongly heated it sublimes in micaceous plates, which are not altered by exposure to the air. It is a compound of
[table]

III. Cadmium combines with iodine when the two substances are heated together; or when they are boiled together in water a solution is obtained. The solution crystallizes in six-sided tables, having nearly the properties of the iodide formed by heating the two bodies in contact. These crystals have a white colour, and are transparent; their lustre is pearly, inclining to metallic, and they are not altered by exposure to the air. When they are strongly heated the iodine is driven off. They dissolve readily in alcohol and water. This iodide is composed of
[table]

IV. Sulphur and cadmium, so far as is known, unite in only one proportion, and the sulphuret, when acted on by nitric acid, is converted into neutral sulphate of cadmium. It is therefore composed of
[table]

It has a yellow colour, inclining to orange. When heated to redness, it becomes, first brown, and then carmine red, but on cooling assumes its original colour. It bears a strong heat without undergoing any change; but in an intense white heat it melts, and crystallizes in transparent micaceous plates of a fine yellow colour. It dissolves readily in concentrated muriatic acid, while sulphuretted hydrogen gas is given out, and no sulphur whatever deposited; but dilute muriatic acid hardly acts upon it even when assisted by heat.

V. Phosphuret of cadmium is gray, and has a weak metallic lustre. It is very brittle, and melts with great facility on burning coals. It burns brilliantly with a strong smell of phosphorus, and is converted into phosphate of cadmium.

Cadmium is precipitated in the metallic state by a plate of zinc, but it throws down lead and all the other metals belonging to the family in which it is placed.

Sect. III.— Of Lead.

Lead is one of the most abundant of all the metals. By far the most common ore of it is galena, or sulphuret of lead; a heavy mineral, having the metallic lustre, a great deal of brilliancy, a bluish-white colour, and a specific gravity of 7∙568. It is soft and brittle, and crystallizes in cubes, and sometimes in octahedrons. This galena is roasted, and then heated on a hearth along with coal and a small quantity of limestone. The lead is reduced and cast into large ingots or pigs. It usually contains silver. When the quantity of that metal present is sufficient to defray the expense, it is put upon a cupel made of bone ashes and a little potash, and exposed in a reverberatory furnace to a blast of air from a bellows placed conveniently. The lead is oxydized, and fused, and blown oft’ in yellow-coloured flakes called litharge, while the silver remains behind upon the vessel. The litharge is again reduced to the state of lead by simply heating it on a hearth along with coal.

Lead has a bluish-white colour, and a good deal of lustre; but it soon tarnishes. It is very soft, and when drawn upon paper leaves a bluish metallic stain behind it. Its specific gravity after fusion is 11∙351. Muschenbroeck affirms that, when drawn out into wire, its specific gravity is diminished. Guyton Morveau assures us, that by hammering lead into a mould, he could increase the specific gravity. But Mr Crichton of Glasgow tried this repeatedly without being able to succeed. Lead is very malleable; it is also ductile, but the wire has but little tenacity. It melts when heated to 606°. By exposure to a very strong heat it may be volatilized.

I. Lead combines with three different proportions of oxygen, and forms three oxides, distinguished by their colour: the protoxide is yellow, the sesquioxide red, and the peroxide brown.

1. Protoxide of lead is easily obtained by dissolving lead in nitric acid, precipitating the solution by carbonate of soda, washing and drying the white precipitate, and then exposing it to incipient ignition. We may form it also by simply exposing good white lead to incipient ignition. It is a light-yellow powder, which is destitute of taste, and insoluble in water, but soluble in nitric and acetic acids, and likewise in potash or soda ley. It melts in a strong red heat, and forms a semitransparent, brittle, hard, glass. This oxide is a compound of
[table]

Litharge, when pure, is nothing else than protoxide of lead. The same oxide is obtained when lead is kept melted in an open vessel, skimming off the surface as it is [7:6:412] converted into ashes, till the whole undergo this change. When these ashes are heated and agitated for a short time in an open vessel, they assume the form of a greenish powder. By continuing to expose this powder to heat it assumes a yellow colour, and is then known in commerce by the name of massico. This massico is nothing else than protoxide of lead.

2. When massico is ground to a fine powder, put into a furnace, and kept constantly stirred while the flame of burning coals plays on its surface, it is gradually converted into a beautiful red powder known by the name of minium or red lead.

Red lead is a tasteless powder, of a beautiful scarlet colour, and having a specific gravity of 9∙096. It loses no sensible weight at a heat of 400°, but when heated to redness it gives out oxygen gas, and is converted into protoxide of lead. It does not combine with acids; but several acids dissolve it by reducing it to the state of protoxide. This happens also when it is dissolved in potash ley.

If we pour vinegar on red lead, and digest it for some time, a portion of protoxide of lead is dissolved, the red lead loses its orange colour, and acquires a dark brownish red hue. It is evident from this that red lead is a mixture of protoxide of lead, which dissolves in the vinegar, and of sesquioxide, which remains undissolved.

The scsquioxidc of lead is a brownish-red powder, destitute of taste, and insoluble in water. When digested in nitric acid, one half of it is converted into protoxide and dissolved, while the remaining half is converted into peroxide and remains undissolved. It is obvious from this that sesquioxide is a compound of
[table]

3. The peroxide of lead remaining when the sesquioxide is treated with nitric acid, has a flea-brown colour, is tasteless, and has a specific gravity of 8 ’ 902. It is not acted on by sulphuric or nitric acid. When digested in muriatic acid, chlorine is disengaged, and chloride of lead formed. When heated it gives out half its oxygen, and is converted into protoxide. When triturated with sulphur it sets it on fire. It is a compound of
[table]

II. When lead is placed in contact with chlorine gas it does not take fire, as is the case with many other metals; but it absorbs the gas, and is converted into a chloride. This chloride is easily obtained by mixing together a solution of 20∙75 parts of nitrate of lead and 7∙5 parts of common salt. A precipitate falls, consisting of small, white, silky crystals. When heated to redness they melt without losing weight, and are converted into a translucent gray matter formerly called plumbum corneum, or horn silver. When heated in the open air it is partly volatile; but when the air is excluded it is fixed at a red heat. It is a compound of
[table]

When this chloride is digested in a solution of potash, one half of the chlorine is abstracted, and a white powder remains, which is a dichloride, composed of
[table]

What is called Turner’s yellow is probably a mixture of this dichloride and of oxide of lead.

III. When a solution of a hydrobromate is dropt into nitrate of lead, a white precipitate falls, having the crystalline appearance of chloride of lead. When strongly heated this matter fuses into a red liquid, which gives out white fumes, and which on cooling concretes into a beautiful yellow substance. This bromide, while a powder, is decomposed by nitric and sulphuric acids, bromine being disengaged; but after fusion it is not attacked by nitric acid, though it may be still decomposed by boiling sulphuric acid. This bromide is doubtless a compound of
[table]

IV. Lead combines readily with iodine when the two substances are heated together. The iodide of lead has a fine yellow colour. It is precipitated whenever a hydriodate is dropt into a solution of lead. It is insoluble in water, but dissolves in potash ley and undistilled vinegar at a boiling temperature, and when the solution cools it falls down in yellow plates. It is a compound of
[table]

V. There seem to be three combinations of sulphur and lead.

1. Sulphuret of lead may be formed by dropping sulphur into melted lead as long as it continues to be absorbed. It exists abundantly native, and constitutes common galena. It has the metallic lustre, and is much less fusible than lead. It is composed of
[table]

When exposed to a red heat in the open air it partly sublimes in the state of sulphate of lead. When mixed with iron and heated, the lead is disengaged, and the iron unites to the sulphur; but by this process it is not easy to obtain the whole lead. A portion is apt to remain mixed with the sulphuret of iron.

2. When a current of dry hydrogen gas is passed over sulphate of lead heated to redness in a glass tube, the lead is reduced to the metallic state, while all the oxygen and half the sulphur of the acid are disengaged. Thus a disulphuret is formed, composed of
[table]

3. Besides the common sulphuret of lead, there occurs another, occasionally, lighter in colour and less brilliant, which burns in the flame of a candle with a blue flame. It is a compound of twelve atoms lead and thirteen atoms sulphur. The simplest view of this galena is to consider it as a compound of eleven atoms sulphuret of lead and one atom bisulphuret of lead. If this view be admitted, it is plain that a bisulphuret must exist, though it has not yet been formed artificially.

VI. Lead and selenium readily unite, and heat is evolved during the combination. The lead swells, and forms a porous mass of a gray colour, which does not melt at a red heat, but is soft, easily polished, and has the whiteness of silver.

VII. Phosphuret of lead is white, with a shade of blue, but soon tarnishes when exposed to the air. It maybe cut with a knife, but separates into plates when hammered.
[7:6:413]

VIII. Arseniet of lead is brittle, dark coloured, and composed of plates.

IX. Lead is hardened by antimony, and the alloy (mixed with a little tin) constitutes printers’ types.

Sect. IV.— Of Tin.

Almost the only ore of tin which occurs native is a dark-coloured, brilliant mineral, very hard and heavy, and known by the name of tinstone. It consists of peroxide of tin, usually contaminated with a little peroxide of iron. This ore, reduced to a fine powder, is mixed with coal and some limestone, and heated strongly in a reverberatory furnace, so as to bring the whole into a state of fusion, which is kept up for about eight hours. The tin is reduced, and falls by its weight to the bottom, where it accumulates, and at the end of about eight hours is let out by tapping a hole in the furnace, which had been filled with clay.

To purify the tin thus obtained, it is put back into the furnace, and exposed to a heat just sufficient to melt it. The pure tin flows out into a kettle, while a quantity of impurities remains behind unmelted. The tin in the kettle is kept in fusion and agitated, by which a quantity of impurity accumulates on the surface. It is skimmed off, and the tin, now refined, is cast into blocks.

Tin has a fine white colour, with a slight shade of blue, and has a good deal of brilliancy. Its hardness is between that of gold and lead. Its specific gravity after fusion is 7∙285∙,∙by hammering it may be made as high as 7∙299. It is very malleable: tin-leaf, or tinfoil as it is called, is about γ0 1 00th of an inch thick, and it might be made much thinner if requisite. It is ductile, but its tenacity is small compared to iron, or even copper or silver. Tin is very flexible, and produces a remarkable crackling noise when bended. It melts when heated to 442°; but a very violent heat is necessary to cause it to evaporate. It soon tarnishes in the air, but undergoes no farther change.

1. Tin combines with two different proportions of oxygen, and forms two oxides, distinguished by their colours, the protoxide being blach i and the peroxide yellow.

1. The protoxide of tin may be obtained by the following process: Digest tin in muriatic acid till a saturated solution is obtained. Precipitate the liquid by means of carbonate of soda; collect the precipitate on a filter, wash it, and press it between folds of blotting paper, and dry it in a temperature not exceeding 180°. By this process a hydrated protoxide is obtained in the state of a white powder. Put it into a small retort, which must (as well as the receiver) be filled with hydrogen or carbonic acid gas; then raise the retort gradually to an incipient red heat. The water will be driven off, and the protoxide remains in an anhydrous state. It is a black powder, without lustre, tasteless, and insoluble in water. When kept dry it is not liable to alter by keeping, but in a moist place it gradually absorbs oxygen, and is converted into peroxide. When heated in the open air it burns brilliantly, and is converted into peroxide. It dissolves in acids without effervescence, and the hydrate more easily than the anhydrous oxide. It dissolves in the fixed alkaline leys, but is insoluble in caustic ammonia and in carbonate of potash, in both which the peroxide dissolves. It is a compound of
[table]

2. The peroxide of tin exists abundantly native, though scarcely ever free from an admixture of iron. It has a yellow colour, and is translucent, or almost transparent, and is crystallized in octahedrons having a square base, or in modifications of that form. Its specific gravity is about 6∙6, and it is as hard as felspar. It is insoluble in acids till it has been fused with an alkali.

It may be obtained artificially by-raising tin to a white heat in the open air. The metal takes fire, and is converted into peroxide. It may be obtained also by treating tin with moderately concentrated nitric acid. A violent effervescence ensues, and the tin is converted into a powder, usually gray; but when heated till the acid is all driven off it becomes yellow. When tin filings and red oxide of mercury are heated together, the peroxide of tin is obtained of a white colour. Peroxide of tin is not soluble in muriatic acid, but it forms with it a combination which is soluble in water. It combines also with sulphuric acid, but the compound does not dissolve. After exposure to a red heat it loses the property of combining with acids. It is a compound of
[table]

Peroxide of tin (when in the state of a hydrate) is soluble in caustic alkalies, and likewise in the alkaline carbonates, which enables us to separate it from the protoxide.

II. Tin combines with chlorine in two proportions, forming two chlorides, one of which has been long known under the name of fuming liquid of Libavius.

1. Protochloride of tin may be formed by heating together an amalgam of tin and calomel, or by evaporating to dryness a saturated solution of tin in muriatic acid, and fusing the residue in a close vessel. It has a gray colour, a resinous lustre and fracture, and takes fire when heated in chlorine gas, and is converted into perchloride. It melts (if air be excluded) rather below a red heat, and does not undergo decomposition. It is soluble in water. It is a compound of
[table]

When the solution of this chloride is mixed with a little alkali, a white powder falls, which is a dichloride, being composed of
[table]

2. Perchloride of tin was discovered by Libavius in the sixteenth century, and was on that account called fuming liquor of Libavius. It is formed when six parts of tin, one part of mercury, and thirty-three parts of corrosive sublimate are mixed together, and distilled by a moderate heat. It is a colourless liquid, like water. When exposed to the air it smokes violently, in consequence of its great avidity for moisture. One part of water and three of the liquid, when mixed, constitute a solid mass. Hence the reason why crystals appear round the cork when fuming liquid is kept in a phial shut with a common cork. It acts with great violence on oil of turpentine. It usually contains an excess of chlorine. When pure, it should be a compound of
[table]

III. Tin and bromine unite in two proportions.

1. Protobromide of tin is obtained by dissolving tin in hydrobromic acid, and evaporating the solution to dryness. It is a compound of
[7:6:414]
[table]

2. When tin is brought in contact with bromine, it catches fire, and is converted into a white solid body of a crystalline texture, which is a bibromide. It is easily fusible, and volatile. It dissolves in water without the evolution of heat. When put into concentrated sulphuric acid it liquefies, and remains at the bottom like oil. Nitric acid disengages bromine from it instantly. It is a compound of ∙
[table]

IV. Iodine combines readily with tin when the melted metal is brought in contact with its vapour. The iodide has a dirty-orange colour, and is very fusible. Water decomposes it, converting it into hydriodic acid and oxide of tin. When tin and iodine are heated together under water, they act on each other and on the water, and are converted respectively into hydriodic acid and oxide of tin. This iodide is a compound of
[table]

V. Tin combines in three proportions with sulphur.

1. Sulphuret of tin may be formed by fusing tin and sulphur together, reducing the matter to powder, mixing it again with sulphur, and fusing it a second time, keeping the temperature sufficiently high to volatilize the superfluous sulphur. It has the colour of lead, the metallic lustre, and is capable of crystallizing. When dissolved in muriatic acid, it is totally converted into sulphuretted hydrogen and protoxide of tin. Hence it is. a compound of
[table]

2. When sulphuret of tin reduced to powder is mixed with the third part of its weight of sulphur, and exposed in a retort to a dull-red heat, it is converted into a sesquisulphuret, composed of
[table]

This sesquisulphuret has a dark yellowish-gray colour, and the metallic lustre; and when rubbed acquires considerable brilliancy. When it is digested in muriatic acid sulphuretted hydrogen gas is evolved, and a yellow matter remains behind, which is persulphuret of tin.

3. Persulphuret of tin has been long known, and was distinguished by the older chemists by the name of aurum mosaicum or musivum, mosaic gold. It may be made by exposing a mixture of twelve parts tin, seven parts sulphur, three parts mercury, and three parts sal ammoniac, to a strong heat in a black-lead crucible. Mosaic gold sublimes. It is in light scales, which readily adhere to other bodies, and which have the colour of gold. When heated it gives out sulphur, and is converted into common sulphuret. It is insoluble in water and alcohol, and is not acted on by nitric or muriatic acid; but when nitromuriatic acid is boiled on it, we gradually decompose and dissolve it. Potash ley dissolves it when assisted by heat, and the solution has a green colour. When an acid is dropt into the solution, a yellow powder is precipitated. This sulphuret is a compound of
[table]

VI. Selenium and tin unite with the disengagement of heat. The tin swells, but does not become liquid. The mass is gray, and has a strong metallic lustre when polished. By heat the selenium is driven off, and the tin remains in the state of an oxide.

VII. Phosphuret of tin is white, and so soft that it may be cut with a knife.

Sect. V.— Of Copper.

Many ores of copper exist; but by far the most common is what is called copper pyrites, which hasa fine yellow colour, and the metallic lustre. It is a compound of copper, iron, and sulphur. This ore is roasted to drive off the sulphur. It is then brought into fusion, which occasions a combination of the oxide of iron in the ore, with a quantity of silica, which is almost always present, or if not, it must be added artificially. This compound separates under the form of slag. What remains after the separation of the slag is called coarse metal. This coarse metal is again roasted for twenty-four hours, which oxydizes the iron, and dissipates the sulphur still remaining. It is now fused again, being mixed partly with slag and partly with furnace bottoms, &c. By this second smelting it is reduced to a matter containing about sixty per cent, of copper. It is now called fine metal.

The fine metal is roasted again, and then smelted a third time. It now contains ninety per cent, of copper, and is called coarse copper. It is exposed to the action of the air, which passes through a furnace at a high temperature. The heat is gradually raised to the melting point, and after from twelve to twenty-four hours it is cast into pigs, known by the name of blistered copper. This copper is again roasted, then melted, the surface covered with charcoal, and a birch pole is plunged into the melted mass. This is repeated till the metal þecomes ductile, and acquires the requisite toughness and closeness of grain.

Copper has a rose-red colour, and a great deal of brilli ancy. Its specific gravity, after being rolled out into plates, is 8∙953. When granulated by pouring it into water while in fusion, the specific gravity is 8 , 895. Its malleability is great, and its ductility very considerable. A bar of cast copper a quarter of an inch thick requires 1192 lbs. to break it; while a bar of hammered copper of the same diameter requires 2112 lbs. to break it. So that hammering almost doubles the tenacity of this metal. It melts when heated to 2548° of Fahrenheit’s thermometer; and if the heat be increased it evaporates in visible fumes. While in fusion its surface is bluish green. It is not much altered by exposure to the weather, and it may be kept under water without alteration.

I. Copper has the property of combining with oxygen∣ in three proportibns, and forms three oxides, two of which occur native; the third is not a permanent compound.

1. Oxide of copper is easily obtained by keeping plates of copper red hot in the open air. Scales gradually form and fall off. When these are collected, reduced to powder, and kept for some time red hot in an open vessel, they are converted into a black powder, which is oxide of copper. We obtain the same oxide by dissolving sulphate of copper in water, and throwing down the copper by carbonate of soda. When the green precipitate is well washed and dried, and then exposed to a red heat, it becomes pure oxide of copper. Oxide of copper is a tasteless black powder, destitute of lustre. It has no taste, and is insoluble in water; but dissolves readily in acids. The solution is blue or green according to the acid employed. Its [7:6:415] specific gravity is 6∙40L When exposed to a very high temperature it melts, and assumes ä crystalline texture. When the solution of it is dropt into an alkaline ley, ablue precipitate falls, which is a sesquihydrate of the oxide. It is insoluble in the fixed alkaline leys; but when fused with fixed alkalies, or alkaline earths, a combination takes place, which is either blue or green according to circumstances. It even displaces carbonic acid at a red heat, but the combination is destroyed by digesting it in water. Caustic ammonia dissolves this oxide, or at least its salts; and the solution has a fine blue colour. Black oxide of copper is a compound of
[table]

2. There is another oxide of copper, which exists native. It has a brownish-red colour, and is crystallized in octahedrons. Its specific gravity is 5 ’ 992. This oxide may be formed artificially by mixing together 57∙5 parts of black oxide and fifty parts of copper in very fine powder. The mixture is put with muriatic acid into a stoppered phial, after having been rubbed in a mortar. Heat is disengaged, and a dark, opaque, brown solution is obtained, from which potash precipitates the oxide in the state of a yellow powder. This oxide is a compound of eight parts, by wcight, of copper, and one part of oxygen. It is of course a compound of
[table]

We may therefore distinguish it by the name of suboxide of copper.

3. When hydrated black oxide of copper is mixed with a dilute deutoxide of hydrogen at the temperature of 32°, the hydrate assumes first a greenish colour, and becomes at last yellowish brown, which is the colour of peroxide of copper. As soon as this oxide is formed, it begins to give out oxygen. It must be separated as quickly as possible from the liquid, pressed between folds of paper, and dried in vacuo over sulphuric acid. When heated to 212° it is decomposed. On a red-hot coal it detonates, and the copper is reduced. It is insoluble in water, and does not alter the colour of litmus paper. It is a compound of
[table]

II. Chlorine, so far as we know at present, combines with copper in two proportions only.

1. Chloride is obtained when the oxide of copper is dissolved in muriatic acid, the green solution evaporated to dryness, and the residual matter exposed to a heat not exceeding 400°. It is a brownish-yellow powder. When exposed to the air it absorbs moisture, and becomes first white and then green. It is composed of
[table]

2. When a mixture of two parts of corrosive sublimate and one part of copper is heated, a resinous-looking matter is obtained, which is a dichloridc of copper. When the solution of suboxide of copper in muriatic acid is sufficiently concentrated, a white salt is obtained, which, when cautiously heated in close vessels, is converted into the same substance. Dichloride of copper has an amber colour, and a certain degree of translucency. It melts at a heat just below redness. It is insoluble in water, but dissolves in nitric acid with effervescence. In muriatic acid it dissolves without effervescence, and is again precipitated when water is added to the solution. Potash throws down suboxide of copper. It may be heated to redness in close vessels without alteration, but in the open air it is dissipated. It is a compound of
[table]

III. Copper unites with iodine when the two bodies are placed in contact and heated. When hydriodate. of potash is dropt into a solution of copper in an acid, a brown precipitate falls, which is insoluble in water, and which seems to be a compound of
[table]

IV. Copper and sulphur appear to combine in three proportions.

1. Disulphuret of copper occurs native, and is known to mineralogists by the name of glance copper. It has a blackish-leaden colour, the metallic lustre is very soft and ductile, and its specific gravity is 5∙792. It is usually crystallized in six-sided prisms, but its primary form seems to be a rhomboid, deviating but a few degrees from a cube. This disulphuret is formed whenever sulphur and copper are heated together. During the combination ignition takes place. It is a compound of
[table]

2. When a current of sulphuretted hydrogen gas is passed through sulphuret of copper, a precipitate falls, which is at first brown, but becomes gradually black. When dried it has a slig*ht shade of green, and slightly reddens litmus paper. When heated it gives out a little moisture, then sulphurous acid and sulphur, and a disulphuret remains. It is insoluble in caustic alkaline leys, and likewise in hydrosulphuret of ammonia. It exists as a constituent of copper pyrites, and is a compound of
[table]

3. When persulphuret of potassium is mixed with sulphate of copper, a liver-brown precipitate falls, which may be washed without alteration in hot water, and which when dry assumes a black colour. It is considered as a compound of
[table]

but has not yet been subjected to analysis.

V. When a current of selenietted hydrogen gas is passed through a solution of sulphate of copper, a precipitate falls in black flocks, which becomes gray when dry, and assumes a polish when rubbed with a hematite. This matter is doubtless scleniet of copper. When it is heated half the selenium is disengaged, and a melted mass remains, probably a diselenict of copper. The selenict is formed also by heating copper and selenium together. It has a steel-gray colour, and melts long before it is heated to redness. When strongly heated it gives out a part of its selenium, but not the whole.

VI. When phosphuretted hydrogen gas is passed over chloride of copper a phosphuret is formed, composed of
[7:6:416]
[table]

A diphosphuret of copper is easily formed by projecting phosphorus into red-hot copper. It is white, brittle, and harder than iron, and is composed of
[table]

WΙιen phosphuretted hydrogen gas is passed over hot di-chlorideof copper,a trisphosphuret is obtained, composed of
[table]

VII. Arsenic has a strong affinity for copper, and unites with it when the two metals arc mixed and heated. The alloy is white and brittle, and is known by the names of white copper and white tombac. The usual alloy is a cli-arseniet, composed of
[table]

VIII. There is an alloy of copper and nickel manufactured at Suhl, in Thuringia, which has a white colour like silver, and is used for a variety of ornamental purposes. It is obtained by smelting an ore composed chiefly of copper and nickel, in the proportion of
[table]

IX. The most important of all the alloys of copper is brass, which is a combination of that metal and zinc. The metals are capable of uniting in various proportions, and according to them the colour and other qualities of the brass vary also. Brass is made by mixing granulated copper, calamine, and charcoal in a crucible. The heat is kept up for five or six hours, and then raised sufficiently high to melt the compound. It is afterwards poured into a mould of granite, edged round with iron, and cast into plates. The most intimate and complete alloy consists of two atoms of copper and one atom of zinc. What is called old Dutch brass is a compound of four atoms copper and one atom zinc.

Brass is much more fusible than copper. It is malleable while cold, unless the proportion of zinc be excessive, but when heated it becomes brittle. It is ductile, may be drawn into fine wire, and is much tougher than copper. The specific gravity varies very much, according to the proportion of zinc which it contains.

X. Tin unites very readily with copper, and forms various useful alloys, differing in name and in properties, according to the proportions of the two metals united.

Bronze and the metal of cannons are composed of from eight to twelve parts of tin combined with a hundred parts of copper. This alloy is brittle, yellow, heavier than copper, and has much more tenacity. It is much more fusible, and less liable to be altered by exposure to the air. The term brass is often applied to this alloy, though in a strict sense it means a compound of copper and zinc.

Bell-metal is usually composed of three parts of copper and one part of tin. Its colour is grayish white; it is very hard, sonorous, and elastic. The greater part of the tin may be separated by melting the alloy, and then pouring a little water on it. The tin decomposes the water, is oxydized, and thrown on the surface.

The alloy used for the mirrors of telescopes was employed by the ancients for the composition of their mirrors. It consists of about two parts of copper united to one part of tin. Mr Mudge ascertained that the best proportions are thirty-two parts of copper to 14∙5 of tin, or
[table]

Vessels of copper, especially when used as kitchen utensils, are usually covered with a thin coat of tin, to prevent the copper from being oxydized, and to prevent the food which is prepared in them from being mixed with any of that poisonous metal. Such vessels are said to be tinned. Their inner surface is scraped very clean with an iron instrument, and rubbed over with sal ammoniac. The vessel is then heated, and a little pitch thrown into it, and allowed to spread over the surface. Then a bit of tin is applied all over the hot copper, which instantly assumes a silvery whiteness. The coat of tin thus applied is exceedingly thin.

Sect. VI.— Of Bismuth.

The most common ore of bismuth is what is called native bismuth, in which the metal exists in an uncombined state. The most abundant ores occur in Germany, where the metal seems to have been first discovered. What of that metal exists in commerce is procured by simply melting the metal out of its gangue, by exposing it to a moderate heat in contact with burning fuel. The metal obtained in this way is never quite pure, but it may be rendered so by the following process: Dissolve it in nitric acid, taking care to render the solution as neutral as possible, and then dilute it with a good deal of water. A white curdy matter falls down, which must be well washed and dried in the open air. When this matter is mixed with black flux, and heated in a crucible, it is reduced to pure bismuth.

Bismuth has a reddish-white colour, and is composed of broad plates adhering to each other. It is rather softer than copper. Its specific gravity is 9∙833. By cautious hammering it may be increased to 9 , 8827. It is not very brittle, yet it breaks when struck smartly with a hammer. It is therefore not malleable, neither can it be drawn out into wire. It melts at the temperature of 497°. When exposed to the air it becomes slightly tarnished, but not sensibly oxydized. But it is oxydized more rapidly when it is exposed to the air in a state of fusion. When raised to a strong red heat it takes fire, and burns with a faint blue flame, and emits a yellowish smoke, which is an oxide of the metal.

I. So far as is known at present, it combines with only one proportion of oxygen, and forms a yellow-coloured oxide. This oxide is best obtained by dissolving bismuth in nitric acid, and mixing the solution with water. A white matter falls, known formerly by the name of rnagis∙ try of bismuth. When this white matter is exposed to an incipient red heat, all the water and nitric acid which it retains are dissipated, and the pure oxide remains. It has a straw-yellow colour, is destitute of taste, insoluble in water, but soluble in nitric acid. In a strong red heat it melts into a dark-yellow, opaque glass, which on cooling assumes its original colour. It is soluble in caustic fixed alkaline leys, and even somewhat soluble in caustic ammonia. It is composed of
[table]

Its specific gravity is 8∙21l.
[7:6:417]

II. Bismuth takes fire when placed in contact with chlorine gas, and forms a chloride. This chloride has been long known by the name of butter of bismuth. It may be obtained by heating a mixture of bismuth and corrosive sublimate. By keeping it in fusion for an hour or two below the boiling point of mercury, that metal gradually subsides, and leaves the chloride of bismuth pure. It has a grayish-white colour, is opaque, and has a granular texture. It does not sublime when heated to redness in a glass tube with a narrow orifice. It is a compound of
[table]

III. When bismuth in powder is heated in a glass tube with a great excess of bromine, yellow vapours appear and condense on the sides of the tube, while a solid bromide remains at the bottom of the tube. It has a steel-gray colour, having the aspect of iodine, fused into a solid mass. It melts when heated to 392°, and assumes a hyacinth colour; but on cooling recovers its original colour. When exposed to the air it absorbs moisture rapidly, and assumes a fine sulphur-yellow colour. Water decomposes it into hydrobromic acid and oxide of bromine, still retaining bromine.

IV. Iodine readily combines with bismuth when assisted by heat. The iodide has an orange colour, and is insoluble in water; but it may be dissolved in a solution of caustic potash without occasioning any precipitation.

V. Sulphur combines readily with bismuth by fusion. The sulphuret has a bluish-gray colour, and crystallizes in beautiful tetrahedral needles, which cross one another. It is very brittle and fusible, and bears a strong resemblance to sulphuret of antimony, but is rather lighter coloured. It occurs native, and is a compound of
[table]

Its specific gravity is 7∙591.

VI. Selenium and bismuth combine with the evolution of heat. The seleniet melts at a red heat, and on cooling has the metallic lustre, a silver-white colour, and a very crystalline texture.

VII. The affinity between phosphorus and bismuth is very feeble. Chemists have not yet succeeded in combining them together, at least in definite proportions.

VIII. Few of the alloys of bismuth are of much importance. What is called the fusible metal of Rose is composed of two parts by weight of bismuth, one part of lead, and one part of tin. It melts when heated to 200° ∙75. What is called Newton’s fusible metal is a compound of eight parts by weight of bismuth, five of lead, and three of tin. It melts at 212°.

Sect. VII.— Of AIercury.

By far the most abundant ore of mercury is cinnabar, in which the metal is combined with sulphur. The cinnabar is mixed with half its weight of lime, or of scales of iron, and distilled in an iron retort, or a kind of oven constructed for the purpose. It comes over for sale in large iron bottles; and while in its original package, the metal may be considered as quite pure.

. Mercury has a white colour, similar to that of silver. It possesses great brilliancy. Its specific gravity is 13∙56846 at the temperature of 60°. When in a solid state the specific gravity is 14∙465. At the common temperature of the atmosphere it is always in a state of fluidity, but it becomes solid when cooled down to — 38° ∙66. Solid mer cury may be subjected to the blows of a hammer, and may be extended without breaking. It boils when heated to 656° on the common thermometer, but the true boiling point is 660°. The specific gravity of its vapour is 6∙9747. Mercury is not altered by exposure to the air, nor by being kept under water; but when kept heated in the open air, or when agitated for a long time in air, it is oxydized.

1. Mercury, so far as we know at present, unites with∣ two proportions of oxygen, and forms two oxides. The suboxide is black, the oxide red.

1. The suboxide was formed by Boerhaave, by putting a little mercury into a bottle, and tying it to the spoke of a mill-wheel. It is a black powder, without any lustre, has a coppery taste, and is insoluble in water. When calomel is digested in an alkaline ley the same suboxide is obtained, but it is very apt to be mixed with globules of running mercury. The best way is to throw a little calomel in fine powder into a considerable quantity of potash ley. It has the property of combining with acids, and forming salts. Its specific gravity is 10∙69. It is very easily reduced to the metallic state. Indeed it almost always contains globules of mercury, which maybe rendered visible under a magnifying glass. It is a compound of
[table]

2. When mercury or its suboxide is exposed to a heat of about 600°, it combines with an additional dose of oxygen, assumes a red colour, and is converted into oxide of mercury. The easiest mode of obtaining this oxide is to dissolve mercury in nitric acid, to evaporate the solution to dryness, and to expose the dry residue to heat in a crucible till all fumes of nitric acid cease to exhale. When thus formed it is usually distinguished by the name of red precipitate.

It has an acrid and disagreeable taste, possesses poisonous properties, and acts as an escharotic when applied to any part of the skin. Its specific gravity is 1 T29. When triturated with mercury it gives out part of its oxygen, and the mixture assumes various colours, according to the proportions of the ingredients. When heated along with zinc or tin filings it sets these metals on fire. When heated to redness it becomes black. It is a compound of
[table]

II. Mercury is said to take fire when it is heated in chlorine gas. It combines with chlorine in two proportions, and forms two important compounds known by the names of corrosive sublimate and calomel.

1. Corrosive sublimate maybe formed by dissolving red oxide of mercury in muriatic acid, and evaporating the solution to dryness. The common method of forming it is to mix together nitrate of mercury, decrepitated common salt, and anhydrous sulphate of iron. One third of a matrass is filled with this mixture. The vessel is gradually heated to redness, when cold corrosive sublimate is found sublimed in the upper part of the matrass. It is a beautiful white translucent mass, composed of small prismatic needles. It is soluble in cold water to the extent of rather more than five per cent, and the solubility increases with the temperature. By evaporation it yields small crystals, the primary form of which is a right rhombic prism, with angles of 93° 44' and 86° 16'. Its specific gravity is 5∙1398. Its taste is acrid and caustic, and it leaves for a long time a disagreeable styptic metallic impression on the tongue. When taken internally, it acts as a virulent poison[7:6:418], producing violent pain, nausea, and vomiting, and corroding the stomach and intestines. Alcohol of 0∙816 specific gravity dissolves about half its weight of this chloride; sulphuric ether dissolves the third of its weight. It is soluble in muriatic acid, but insoluble in sulphuric and nitric acids. The fixed alkalies decompose it, throwing down the oxide of mercury in the state of a yellow powder, which soon becomes brick red. It is composed of
[table]

2. When four parts of corrosive sublimate are triturated with three parts of running mercury till the mercury is hilled, as the apothecaries term it, that is to say, till no globules of the metal can be perceived, and the whole is exposed to a strong heat in a matrass, calomel is sublimed, usually mixed with a little corrosive sublimate, from which it may be freed by washing.

Calomel, or subchloride of mercury, is usually in the state of a dull white mass, but when slowly sublimed it crystallizes in four-sided prisms terminated by pyramids. The primary form seems to be a square prism. It is tasteless, does not act as a poison, but possesses the properties of a purgative. It is by far the most useful and important of all the medicinal preparations of mercury. Its specific gravity is 7T758. It is not sensibly soluble in cold water. When exposed to the air it becomes deeper coloured. When rubbed in the dark it phosphoresces. It requires a stronger heat for sublimation than corrosive sublimate. When mixed with one part of common salt and two parts of anhydrous sulphate of iron, and sublimed, it is converted into chloride. It is a compound of
[table]

III. Bromine and mercury unite in two proportions, forming compounds analogous to the chlorides.

1. When an alkaline hydrobromate is mixed with a solution of nitrated suboxide of mercury, a white precipitate falls, analogous to calomel. It is a compound of
[table]

2. When bromine and mercury are placed in contact, they readily combine, heat being evolved, but no light. A white matter is obtained, which may be sublimed by heat, and which is soluble in water and in alcohol, and very soluble in ether. Alkalies throw down a red or yellow precipitate from its aqueous solution. When heated with nitric or sulphuric acid it gives out vapours of bromine. It is composed of
[table]

IV. Iodine combines readily with mercury, nothing more being necessary than to bring the two bodies in contact. An iodide is formed also when a hydriodate is drop! into a solution of mercury in an acid. There are two iodides of mercury. The subiodide (analogous to caľomcD has a yellow colour, while the iodide is red. They arg i bθ1th z ih-soluble in water, and decomposed by nitric acid.. The subîódide is r c ’ o ’ mposed of , ’ ' ’, i
[table]

the iodide of
[table]

V. Sulphur also unites in two proportions with mercury. The sulphuret is red, the disulphuret black.

1. When two parts of sulphur and one of mercury are triturated together in a mortar, the mercury gradually disappears, and a black powder is formed, formerly called ethiops mineral. It is scarcely possible to unite all the mercury with the sulphur by this process. We succeed better by heat. When mercury is added slowly to its own weight of melted sulphur, constantly stirring the mixture till the excess of sulphur is driven off, we form a more intimate compound. When a current of sulphuretted hydrogen is passed through a solution of mercury in an acid, the same black subsulphuret falls. It is a black, tasteless powder, insoluble in water, and very easily decomposed. It is a compound of
[table]

2. When ethiops mineral (containing an excess of sulphur) is heated red hot, it sublimes, and a cake is obtained of a deep-red colour, composed of fibres or small prisms. This cake is distinguished by the name of cinnabar, and when in powder it is called vermilion. Sulphuret of mercury thus formed has a specific gravity of 10. It is tasteless, insoluble in water and in muriatic acid, and not altered by exposure to the air. When heated it takes fire, and burns with a blue flame. When mixed with iron filings, and heated in a stoneware, retort, it is decomposed, sulphuret of iron is formed, and running mercury is distilled over. Cinnabar, when in powder, has a scarlet colour, and is well known as a paint. It is a compound of
[table]

VI. Selenium and mercury, when heated together, combine without the evolution of light. Seleniet of mercury is a tin-white, coherent mass. It does not mplt, but sublimes, when heated in thin plates which have the metallic lustre. It is scarcely attacked by nitric acid; but when long boiled in that acid, it is at length converted into seleniate of mercury. In this state it is decomposed by muriatic açid, selenium being left in the slate of a red powder. Nitromuriatic acid dissolves the seleniet rapidly, even without the assistance of heat.

VII. Phosphuret of meŗcyry is black, .of a pretty solid consistence, and capable of being cut with a kiļĩfe.

VIII. The compounds which mercury makes with the metals are usually called amalgams. Mercury easily dissolves gold, silver, zinc, cadmium, bismuth, tin, and lead. With rather more difficulty it may be united to copper and platinum. With arsenic and a,ntimpny it. may be united by trituration, assisted by heat. With, iron it cannot be united directly; accordingly mercury is usually kept in iron vessels. , , , ,∣ ∙ .. ∣ ∣∣ ∙

>' ’ >o 4Sec⅛. VIII.— Of Silver.''^ " t l '

Silver exists in the, earth ve 1 ry frequently in the metallic stat,e in smJl tĩìŗęądą.or crystals, interspersed, with rocky ∣matter, p∙qq∣ γ.D⅛q it iş.'cĢµed’ęd .by agitation with mprcury. ' Tliat 1 qte,tal ttissoĮy£^ttogI⅞∖lvg⅛ and the amalgam being exposed tq ι t, lις requisite,, heat, the,n1crc⅛ry.is driven off, and the, silver remains įh a state of purity, ju [7:6:419] Silver is a metal of a fine white colour, with a slight shade of yellow. It has a great deal of brilliancy and beauty when polished. It is softer than copper, but harder than gold. When melted, and cooled slowly, its specific gravity is 10-3946; when hammered and rolled, it becomes as high as 10∙1S12. It is very malleable and ductile, but its tenacity is inferior to that of copper. It melts when exposed to a strong red heat, and while in fusion its brilliancy is much increased. Its melting point, as determined by Princeps, is 1830°. It is not altered by exposure to the air, unless fumes of sulphur or sulphuretted hydrogen gas happen to exist in the atmosphere. Water produces no alteration on it.

I. Silver seems capable of combining with three doses of oxygen, and of forming three oxides, two of which are neutral bodies, while the third possesses the characters of an alkaline body on base.

1. When silver is dissolved in nitric acid, and a fixed alkali added to the solution, a brown-coloured powder falls, which becomes darker when dried. It is tasteless and insoluble in water, nor is it capable of forming a hydrate. Its specific gravity is 7∙143. When exposed to the direct rays of the sun it gives out oxygen, and becomes black. Caustic ammonia, when digested on it, dissolves it partially, leaving a black powder, which is fulminating silver. It is a compound of
[table]

2. When oxide of silver is dissolved in ammonia, and the solution left exposed to the. open air, it is soon covered with a brilliant pellicle. If this be removed another succeeds, and almost the whole of the dissolved oxide may be made to undergo this change. This matter by reflected light appears gray, by transmitted light brown. When suddenly heated it melts, gives out oxygen, and leaves a button of silver. It is a compound of
[table]

This suboxide does not appear capable of combining with acids.

3. Superoxide of silver is formed when a platinum wire from the positive extremity of a galvanic battery is plunged into a weak solution of nitrate of silver. It constitutes small brilliant crystals on the platinum wire, and has a black colour. When held to the flame of a candle it detonates, and leaves metallic silver. When it is digested in sulphuric or phosphoric acids, oxygen gas is given out, and sulphate or phosphate of silver formed. It obviously contains more oxygen than the brown oxide, but it has not hitherto been subjected to analysis.

II. So far as is known, silver combines with only one proportion of chlorine, and forms the well-known compound formerly known by the name of horn silver, lima cornea, and now by that of chloride of silver. When solutions of nitrate of silver’ and common salt are mixed together, a copious white curdy precipitate falls, which when washed and dried constitutes chloride of silveri It is tasteless, and insoluble in water; but dissolves readily in caustic ammonia. Its specific· gravity is 5∙552. It occurs native, and is crystallized in octahedrons. Its colour is white, but when exposed to the air it gradually assumes a purple colour. At the temperature of about 500° it melts, and on cooling assumes the form of a light-brown, translucent glass, having some resemblance to horn in point of toughness. Inaveryhigh temperature itsublimes. When exposed to a current of nascent hydrogen gas, it is reduced to the metallic state. It is converted into metallic silver also when heated to redness, surrounded with common potash of commerce in a crucible; or we may obtain reduced silver from it, by putting it into a vessel of zinc, or east iron, along with a little water. Copper, iron, lead, tin, zinc, antimony, and bismuth, when fused along with it, unite with the chlorine, and leave the silver in the metallic state. This chloride is a compound of
[table]

III. When nitrate of silver is dropt into a solution of a hydrobromate, a bromide of silver falls down in light-yellow curds. When exposed to the light it blackens, but not so readily as chloride of silver. It is insoluble in water and in nitric acid, but soluble in ammonia. Boiling sulphuric acid disengages some vapours of bromine from it. When heated it melts into a reddish liquid, which on cooling recovers its original colour, and assumes the appearance of horn. Nascent hydrogen decomposes it as it does chloride. It is a compound of
[table]

IV. The iodide of silver is easily obtained by mixing a hydriodate with a solution of nitrate of silver. A greenish-yellow, curdy precipitate falls, having considerable resemblance to chloride of silver. It is insoluble in water, and easily decomposed when heated with potash. It is a comnound of
[table]

V. Sulphur has a strong affinity for silver. When thin plates of silver and sulphur are laid alternately in a crucible, they melt readily at a low red heat, and constitute a sulphuret. It is black, or at least of a very deep violet colour, capable of being cut with a knife; often crystallized in small needles, and much more fusible than silver. By heat the sulphur may be slowly volatilized, and the silver left pure. This compound frequently occurs native. It has a dark-gray colour, the metallie lustre, and the softness, flexibility, and malleability of lead. Its specific gravity is about 7∙'2. It is a compound of
[table]

VI. Selenium and silver seem capable of combining in two proportions. When the two substances are heated together, they unite with the evolution of heat, and a very fusible compound is formed, from which the excess of selenium may be separated by distillation. This seleniet is gray, and while in fusion its surface is brilliant, like a mirror. It melts long before it is heated to redness. It possesses some malleability, and may be a biselenict.

When silver is precipitated by selenietted hydrogen, it falls in the state of a black powder, which becomes dark gray when dried. This 'seleniet requires a red heat to fuse it, and does not give out any selenium when distilled.

VII. Phosphuret of silver has a white colour and a granular texture. It breaks under the hammer, but may be cut with a knife. It seems to be a compound of
[table]
[7:6:420]

VIII. Arseniet of silver is steel-gray, brittle, and fine granular.

IX. There are few of the alloys of silver of much consequence. It would appear from the experiments of Stodart and Faraday, that the quality of steel is improved by the addition of a little silver. Silver readily unites with copper by fusion, and the colour of the silver is not sensibly altered, even when the copper amounts to half the weight of the silver. The standard sterling silver of Great Britain is an alloy of 12^ by weight of silver, and one of copper. This is very nearly a compound of three and a half atoms silver and one atom copper. The specific gravity of this alloy, after simple fusion, is 10∙200. When stamped into coin its specific gravity is 10∙3121. The weight of a shilling is 87*55 grains.

FIFTH FAMILY.—NOBLE METALS.

The name of this family has been given to it because it contains gold and platinum, and because the other four metals belonging to it are usually associated with native platinum.

Sect. L— Of Gold.

Gold always occurs in the metallic state, seldom pure, but usually alloyed with silver or copper, or with both, and sometimes, it is said, with platinum. From copper it may be freed by cupellation, and from silver by solution in aqua regia, and mixing the solution, which contains only the gold, with a recent solution of sulphate of iron. The pure gold is thrown down in the state of a fine powder, which has only to be washed and fused.

. Gold has a beautiful yeljow colour and considerable lustre, which it retains, not being liable to tarnish by exposure to the air. It is rather softer than silver. After fusion it has a specific gravity of 19∙2, but by hammering it may be made as high as 19*361, or perhaps 19∙4. It is the most malleable of all metals, and may be beaten out into leaves no thicker than ^2 l 000 °f an dich, a ŋd the gold leaf with which silver wire is covered is only -⅛th of this thickness. It may be drawn out into very fine wire, and its tenacity is considerable, though inferior to that of silver. It melts, according to Davies, when heated to 2590° Fahrenheit. It is not soluble in any acid; neither sulphuric, nitric, nor muriatic have any action on it, but it dissolves with great ease in aqua regia. The solution has a yellow colour, an acrid taste, and is very poisonous.

Į. We are acquainted at present with only two oxides of gold, which, however, are not easily obtained in a separate state.

1. The peroxide of gold may be obtained by the following process: Dissolve gold in an aqua regia composed of a mixture of one part of nitric and four parts of muriatic acid. Render the solution as neutral as possible by evaporation ,∙ 1 then add potash, and heat the liquid. ..A voluminous precipitate gradually falls, which must be carefully washed and dried. It is now peroxide of gold, but not quite free from potash. If we add magnesia to the solution of gold in aqua regia, a precipitate falls, consisting of oxide of gold united to magnesia. When this precipitate is washed and digested in nitric acid, the magnesia is diśsolved, together with part of the gold, and pure öxidb of gold remains undissolved. Peroxide of gold, when in the state of hydrate, is a light-yellow powder;, but when anhydrous it is brown or black. It dissolves ,readily in muriatic acid, and the solution has a fine ŷ'elloŵïsh-rėd colour. At an incipient red heat it’ is deprived of its" oxygen,' and the gold is reduced to the metallic’ statb. This oxide is a compound of , ' l ; r - hh ' ⅛ 1 ∕ luι . l ' lv ' tii,tl
[table]

2. When the solution of gold in muriatic acid is heated till it ceases to give out chlorine gas, a straw-yellow mass remains, which is insoluble in cold water. When this substance is treated with caustic potash, a green-coloured powder is separated, which is suboxide of gold. In a short time it divides itself into two parts; one third deprives the other two thirds of the whole of their oxygen, and becomes peroxide, while the other two thirds are reduced to the metallic state. From this it is obvious that the suboxide is a compound of
[table]

It does not seem capable of uniting either with acids or bases.

II. When gold-leaf is exposed to the action of chlorine gas, a combination takes place. When the solution of gold in aqua regia is sufficiently concentrated, ruby-red crystals shoot, so deliquescent that they cannot be preserved. These crystals (abstracting the water) are composed of
[table]

When a solution of gold in aqua regia is cautiously evaporated till the colour becomes brown, it becomes a solid mass on cooling, and a portion of the gold is disengaged from its combination. The brown chloride is a compound of
[table]

When the heat is continued longer and carried farther, the sesquichloridc may be converted into a dichloride, composed of
[table]

The feesquichloride of gold possesses the characters of an acid.

∏L Bromine and its aqueous solution are capable of dissolving gold. A yellow bromide is thus obtained, which stains animal bodies purple. Heat decomposes it into bromine and metallic gold. ∣ t

IV. Iodide of gold may be obtained by mixing together! chloride of gold and hydriodate of potash, taking care to heat the liquid, in order to drive off the excess of iodine which falls with the iodide of gold. Iodide of gold is insoluble in cold water, and but little soluble in boiling water. Muriatic, nitric, and sulphuric acids, do not decompose it cold; but when it is boiled iń these acids in a concentrated stħte the gold is reduced, and the iodine disengaged. Heat decomposes it at a temperature no higher than 300°. Alkaline solutions decompose' it immediately. According to Pelletier, it is a trisiodide, composed of
[table]

V. Sulphur, even when assisted, by héàtý has no action on gold ;' nor is ĩt’'ever Fd,find combined wit⅛ sulphur, as is the caíśe'wïtlì mó^t’ other, tíiėtáIs; yet it’ìńäy be made to combine .With it’¢ĩmply by piixinb'togethcr sulphohydrate [7:6:421] of potash and solution of sesquichloride of gold. A black powder falls, which is a sesquisulphuret of gold, composed of
[table]

It is exceedingly difficult to dry this sulphuret without acidifying the sulphur.

VI. Phosphurct of gold is brittle, whiter than gold, and seems to be capable of crystallizing.

VII. Arsenic has a strong affinity for gold, and a very minute quantity of it renders that ductile metal quite brittle, like glass. Antimony has the same property. Gold is also rendered brittle by being alloyed with nickel, cobalt, zinc, bismuth, lead, and tin. With iron, manganese, copper, and silver, it forms ductile alloys. Copper gives it a red colour, and considerably improves its beauty. What is called sterling gold, which is the standard of the gold coin of Great Britain, is an alloy of twelve parts of gold withone part of copper or silver, or sometimes a mixture of the two.

Sect. II.— Of Platinum.

This metal occurs in small, white, metallic plates, in alluvial soil, which consist of platinum alloyed with a considerable number of other metals. It was first brought to the form of an ingot by Dr Wollaston. The process followed was the following: The crude platina must be. digested in dilute aqua regia till the acid is as nearly saturated with platinum as possible. Then draw off the liquid, and allow it to stand till a fine powder of ore of iridium has subsided. Then mix it with sal ammoniac previously dissolved in five times its weight of water. A yc!low precipitate falls, which must be thoroughly washed, and ultimately pressed to remove the last remnant of the washings. It is next to be heated with extreme caution in a blâck-lead pot,'just sufficiently high to drive off the sal ammoniac, and to oéc’asion the particles of platinum to adhere together as little as possible. The gray product of platinum is now to be rubbed between the bauds to reduce it to a powder fine enough to pass through a lawn sieve. The coarse parts are then to be ground in a wooden bowl with a wooden pestle, till the whole is reduced to powder. They must not be touched with any thing hard enough to burnish their surface, otherwise the process is spoilt. The powder is now to be put into a brass mould filled with water, taking care that no vacuities are left. The top of the powder is first covered with a circle of paper, and then with one of cloth; and it is then pressed, first by the hand with a wooden instrument, and afterwards by’ means of a powerful press. It is then placedin a çharcoaľ fire, and there heated to redness. It is now covered with á crucible, not touching it, and exposed for about twenty' minutes to the highest temperature that can be raised in a wind furnace. 1 ' Finally, it is placed on an anvil, and struck when hot with a heavy hammer,’ always on tķe end, and so as effectually to close the metal at one heat. > ' It mus£ never be struck on the sides, which would 'cause it to crack. , 1 '' ' ' , : l· .l’ ∕

Platinum has a whitecolour, like silver, but without the shade of yellow which characterizes that metal. Its hardness is intermediate between that of copper and iron. Its specific gravity, while in the state of powder, is 21∙47. By hammering it may be. made as high as,,21∙5313.y It is very ductile and malleable, thqugh much Jess só than gold. Its tenacity is considerable. ., It. re^ist^, the highest température of air furnaces, .without melting, but,.it may be fused by the action of the oxyliydfogen blowpipe.

Like gold, it resists the action of all the single acids; but it dissolves readily in aqua regia, and the solution has a yellowish-brown colour and an astringent taste.

I. It seems to be capable of combining with two doses ( of oxygen, and of forming two oxides, or perhaps three, which, however, are not easily procured in a separate state.

1. To obtain protoxide, the solution of platinum in aqua regia is to be evaporated to dryness, and the dry mass exposed in a porcelain cup to the temperature at which tin melts. Chlorine gas is given off, and a gray powder remains, which must be digested in a solution of potash. A black powder remains, which, when well washed and dried, is considered as protoxide of platinum. It is a hydrate. When heated in a retort it gives out water and oxygen gas. When heated to redness with combustible bodies it detonates feebly. Acids reduce it to metallic platinum and peroxide. It is a compound of
[table]

2. To obtain peroxide of platinum is exceedingly difficult. When a current of sulphuretted hydrogen gas is passed through a neutral solution of chloride of platinum, a black precipitate'falls, which is sulphuret of platinum. Wash it, and dissolve it in nitric acid; evaporate the solution, and continue the heat till all the nitric acid is driven off. Sulphate of platinum remains. Dissolve it in water, and throw down the sulphuric acid by nitrate of barytes, then filter, and pour caustic potash into the liquid. Onc half of the platinum falls in the state of peroxide; the remainder, constituting a double salt, remains in solution. Peroxide of platinum thus obtained has a yellowish-brown colour, and is bulky. When dried it becomes darker coloured, and then has a considerable resemblance to rust of iron. It is a hydrate. When heated it gives out water, and becomes almost black. At an incipient red heat it gives out oxygen, and the platinum is reduced. It is a compound of
[table]

3. When a neutral solution of mercury is poured into a dilute solution of chloride of platinum, a dense precipitate falls, which is a mixture of calomel and suboxide of platinum. Expose it to a heat just sufficient to drive off the calomel. A deep-black powder remains, which, according to Mr Cooper, is composed of
[table]

It is therefore á suboxide.

II. Platinum does not take fire when introduced into chlorine gas, but it irnbibes the gas, and is converted into a chloride. Two chlorides of platinum are at present known.' ,' , ' ι

1. P.rotpchļqride may be obtained by boiling platinum in. strong muriatic acid, adding occasionally a little nitric. Evaporate the solution to dryness, and digest it with a little muriatic acid, t which is likewise to be driven off. The dry mass, is to be cautiously heated nearly to redness, and boiled with a considerable quantity of water. ’ Being now dried, it is pure chloride of platinum. r ,

Its colour is dull olive-green. It has a harsh feel, and i⅛ (lestitμt^ of taste 1 and ,smell. It does not melt when heated, nor is it altered by exposure to the atmosphere. It is insoluble in water, but dissolves in perchloride of platinum[7:6:422]. It is slightly soluble in boiling muriatic acid; but it is soluble, in nitric, sulphuric, phosphoric, and acetic acids. It is a compound of t ∙i
[table]

2. Perehloride of platinum is obtained by dissolving platinum in nitromuriatic acid, and cautiously evaporating the solution to dryness, to drive off all excess of acid. A reddish-brown matter remains, which dissolves in water, forming the well-known reddish-brown solution employed by chemists for separating potash from soda. It is a compound of . .
[table]

III. Platinum does not act upon bromine or its vapour at the ordinary temperature of the atmosphere; but it dissolves in bromonitric acid, and a yellow-coloured bromide is formed, decomposable, and capable, like the perchloride of platinum, of forming insoluble yellow precipitates in salts of potash and ammonia.

IV. When iodic acid is dropt into a solution of bichloride of platinum, a yellow-coloured iodide falls, somewhat soluble in water.

V. Platinum seems capable of uniting with a little silicon when strongly heated surrounded with charcoal. Its specific gravity is diminished, it assumes a gray colour, and loses much of its malleability. In the same way it unites with a little boron, which has a similar effect upon it.

VI. Platinum combines with three proportions of sulphur, and forms three sulphurets, which were first investigated by Mr Edmund Davy.

1. Protosulphuret of platinum is formed by mixing equal weights of sulphur and platinum in an exhausted glass tube, and heating them together, raising the temperature at last till all the superfluous sulphur is driven off. It has a dull bluish-gray colour, and acquires the metallic lustre when burnished. Its specific gravity is 6∙2. It is a nonconductor of electricity, and is decomposed when heated with zinc filings. It is probably a compound of
[table]

2. When platinum is precipitated from its solution in aqua regia by a current of sulphuretted hydrogen gas, a black sulphuret is obtained, which must be dried in vacuo over sulphuric acid, otherwise it absorbs oxygen, and is converted into sulphate of platinum during the drying. ArΩ∩rdin<r tn Mr K. Γ)nw. it is ∩ ponmnnnd ∩f
[table]

3. Persulphuret of platinum is obtained by heating a mixture of three parts of ammonia-chloride, of platinum, and two parts of sulphur, in a glass retort. The heat must be gradually raised to redness, and kept at that point till every thing volatile is expelled. It has a dark,, iron-gray colour, approaching to black. When in lumps it has a slight metallic lustre. It has a soft feel, and when rubbed on paper leaves a stain similar to that of black lead. M hen it is heated with zinc filings, combustion takes, place, and sulphuret of zinc is formed. When heated to redness in the open air the sulphur is driven off, and the platinum remains in the metallic state. It is a compound of
[table]

VII. Selenium combines with platinum in powder when the mixture is heated. Much heat is evolved. The seleniet formed is gray, and has not undergone fusion. Heat drives off the selenium, and leaves.the platinum in the metallic state.

VIII. The affinity between platinum and phosphorus is so great that if we heat a phosphate mixed with charcoal in a platinum crucible, we destroy the crucible by converting it into a phosphurct. There seem to be three phas-phurets, but their constitution has not yet been determined with accuracy.

IX. The alloys of platinum, so far as we know them at present, are not of much importance. With antimony it combines readily, and forms a brittle alloy. An alloy ol seven parts platinum, sixteen copper, and one zinc, has much the appearance of pure gold. Platinum is not easily amalgamated with mercury, but the combination may be accomplished by triturating a little powder of platinum with mercury in a mortar, adding each constituent by small quantities at a time, as required.

Sect. III.— Of Palladium.

This metal was originally discovered by Dr Wollaston in crude platinum; but it seems to exist in Brazil in considerable quantity, for large ingots of it were brought some years ago from that country to London, to see whether they 7 could find a market. It may be thrown down from the solution of crude platinum in aqua regia by prussiate of mercury. The precipitate has a pale-yellow colour. When washed, dried, and exposed to a red heat, palladium remains in powder. It may be fused with sulphur into an ingot, and by cautious roasting the sulphuris driven off, and the palladium may be hammered into a solid mass. Much patience and perseverance is necessary before the cake can be made to bear hard blows.

Palladium is a white metal, which, when polished, bears a very strong resemblance to platinum. It is rather harder than wrought iron. Its specific gravity, after ignition, is 10-972, but by hammering it may be made as high as 12∙148. It is very malleable and ductile, possesses but little elasticity, and is not altered by exposure to the air while cold. At a red heat it speedily acquires a blue colour on the surface, but loses it when exposed to a still higher temperature. The best solvent of it is aqua regia. The solution has a rcddish-brown colour, somewhat similar, but darker, than that of chloride of platinum.

I. It seems to be capable of uniting with two proportions of oxygen, and of forming two oxides. >

1. The protoxide may be obtained by fusing palladium in powder with potash and a little nitre, or by dissolving palladium in fuming nitric acid, evaporating to dryness, and exposing the residual salt to a heat approaching ignition, to drive off the nitric acid. It is a black, tasteless pow 7 der, which is insoluble in water. It does not readily dissolve in acids, and requires boiling before we can obtain a complete solution in muriatic acid. When precipitated from nitric acid by an'alkali, we obtain it in the state of a brownish-yellow hydrate. It seems to be soluble in alkaline leys. It is a compound cf
[table]

The peroxide .of palladium has not yet been obtained in a separate state.
[7:6:423]

II. The chlorides of palladium, like the oxides, are two.

1. Protochloride may be formed by dissolving protoxide of palladium in muriatic acid, and evaporating to dryness. In this state it has not been examined, but it has the property of uniting like an acid with chloride of potassium and sal ammoniac, and of forming salts which have been analysed. From these analyses the chloride appears to be a compound of
[table]

2. The perchloride of palladium has not yet been examined in a separate state, but is obtained united to chloride of potassium by dissolving chloropalladiate of potassium in aqua regia, and evaporating the solution to dryness. The salt is obtained in small red crystals. This perchloride is a compound of
[table]

The bromide and iodide of palladium remain still unknown.

III. Palladium unites very readily to sulphur. When it is strongly heated, the addition of a little sulphur causes it to run into fusion immediately, and the sulphuret continues in a liquid state till it is only obscurely red hot. Sulphuret of palladium is rather paler than the pure metal, and is extremely brittle. By means of heat and air the sulphur maybe gradually driven off, and the metal obtained in a state of purity. This sulphuret appears to be a compound of
[table]

IV. Palladium and selenium unite with facility, and heat is disengaged during the combination. The compound is gray and coherent, but has not undergone fusion. Before the blowpipe selenium is disengaged, and the alloy fuses into a grayish-white metallic button, which is brittle, and has a crystalline fracture.

V. Lead, tin, bismuth, and iron, when alloyed with palladium, render it brittle. With gold, platinum, and silver, 1 it forms malleable alloys. The alloy with copper is rather brittle.

Sect. IV.— Of Rhodium.

Rhodium, like palladium, exists in crude platinum, from which it was first extricated by Dr Wollaston. It exists only in minute quantity, and of consequence has been but imperfectly examined.

After freeing the solution of crude platinum in aqua regia, of its platinum, by means of sal ammoniac, a plate of clean zinc was immersed in the liquid, which precipitated a black powder. It was washed and digested in dilute nitric acid, to dissolve some copper and lead which it contained. It was then dissolved in nitromuriatic acid. Common salt being added to the solution, the whole was evaporated to dryness, and the-residual salt washed with alcohol by small quantities at a time, till it came off nearly colourless. There remained chloride of rhodium united to common salt. When this salt is dissolved in water, and a plate of zinc immersed in the solution, á black powder falls, which iŝ rhodium. When strongly heated with borax it becomes white, and assumes the metallic lustre.

Rhodium has a white colour, like that of platinum. Its specific gravity is 10∙649. It is brittle, and requires a much higher temperature to fuse it than any; other ímétal, unless iridium be excepted. It has the remarkable property of being insoluble in all acids, even in aqua regia. It is exceedingly hard, being in this respect superior to any other metal. Dr Wollaston employed those persons who in London were accustomed to cut and polish diamonds, to cut it into pieces fit for being applied to the nibs of pens. They assured him that it spoiled their instruments much more than the diamond itself.

I. Rhodium appears capable of combining with two proportions of oxygen, and of forming two oxides.

1. The peroxide may be obtained by precipitating chlororhodiate of sodium by caustic potash, taking care not to add an excess of the alkali. Yellow flocks fall, which constitute the peroxide. When dried it assumes a brown colour, and is never free from the precipitating alkali. When strongly heated it becomes black; but whether this change is accompanied with the evolution of oxygen has net been ascertained. There is reason to suspect that this oxide (for it has not been analysed) is a compound of
[table]

2. When sulphurous acid is added to chlororhodiate of potassium, a pale-yellow powder gradually falls, which becomes nearly white when dried. When carbonate of soda is mixed with a solution of this salt, a gelatinous oxide precipitates, of a deep greenish-yellow colour. This precipitate has been considered as a protoxide of rhodium, but it has not yet been subjected to analysis.

II. There are two chlorides of rhodium, which, however, have not yet been obtained in a separate state, but only in combinations with chlorides of potassium and sodium. The first seems to be a compound of
[table]

The perchloride seems to be a compound of
[table]

The other combinations of rhodium with simple bodies remain still unexamined. It combines easily with sulphur, and in that way is rendered fusible. It unites also easily with arsenic. With gold and silver it forms malleable alloys. With steel it may be united in almost any proportion. Faraday and Stodart formed an alloy of two atoms steel and one atom rhodium, which formed an excellent metallic mirror, exhibiting a surface of admirable beauty, and not liable to tarnish.

Sect. V.—Of Iridium.

There is an ore of iridium, in small, flat, metallic plates, having a specific gravity of 19∙25, and mixed with the plates of native platinum. When crude platinum is dissolved in aqua regia, it leaves behind it a heavy black powder, of rather à complicated nature, but containing, among other constituents, a considerable proportion of iridium. It was from this powder that Mr Tennant, the discoverer of the metal, first extracted iridium. His process was to beat the black powder in a silver crucible,'with its own weight of potash. Water dissblves off' the pó’tash of a deep-otange colour; the undissolved i portion being ^digested in ’ mnriatic acid, that aċid beconics ’ first blue, theń olive-green, and’lastly deep red: The hr⅛dissdlvc⅛portibn is again treated with potash and with τmri⅛ιi'c acid alternately, till the whole 1 is dissolved. By th’is prôcċ¾s two [7:6:424] solutions are obtained; the alkaline, of a deep-orange colour, containing the osmium ; and the muriatic acid solution, of a deep-red, containing the iridium. This last solution, by concentration, yields octahedral crystals of chloride of iridium. A plate of zinc throws down a black powder from the solution of these crystals. When heat is applied to the powder it becomes white, and assumes the metallic lustre. In this state it is pure iridium.

. Iridium has the appearance of platinum. It has only been obtained in the state of powder, so that we do not know whether it be malleable or brittle; neither has its specific gravity been determined, though there is reason to believe that it is as high, if not higher, than that of platinum. It resists the action of all acids, even the nitromuriatic, almost completely, more than 300 parts of that acid being necessary to dissolve one part of iridium.

I. The affinity between iridium and oxygen seems to be considerable. It has been conjectured by Berzelius that it combines with four doses of oxygen, and forms four oxides, though hitherto these four oxides have not been obtained in a separate state.

1. The protoxide may be obtained by boiling the protochloride with concentrated solution of caustic potash. The protoxide separates in the form of a black powder, which is scarcely acted on by acids, though it communicates to them a light-green colour. The hydrate of this oxide, obtained by precipitating protochloride of iridium with carbonate of potash, is a bulky greenish-gray matter, which is rc-dissolved by an excess of carbonate of potash. The hydrate dissolves in acids when assisted by heat, and forms salts of iridium. This oxide is probably a compound of
[table]

2. Sesquioxide of iridium may be obtained by mixing bichloro-iridiate of potassium with its own weight of carbonate of potash, and heating the mixture in a close vessel to incipient ignition, taking care not to elevate the temperature too high, which would occasion the expulsion of the carbonic acid, and the combination of the acid with the alkali. When the saline mass is dissolved in boiling water and filtered, it leaves on the filter a blackish-blue powder, which is the sesquioxide. When washed with pure water it passes through the filter. It should therefore be washed with a solution of sal ammoniac, the last traces of which may be driven off by heat. It is a darkbrown powder, composed of
[table]

3. The existence ofbinoxide of iridium is only inferred from analogy. It would seem to possess acid characters, as it combines with bases. Its constituents are no doubt
[table]

4. Teroxide of iridium is obtained by adding carbonate of potash or soda to red chloro-iridiate of potassium free from ammonia. By digestion a gelatinous hydrate falls, which when collected on the filter is brownish yellow or greenish, and so similar to the hydrated oxide of rhodium that it is impossible to distinguish them from each other by their appearance. This oxide dissolves in muriatic acid, and when the solution is concentrated it becomes red. It has not been analysed, but from analogy it is probably a compound of
[table]

II. Chlorine and iridium have a strong affinity for each other. They combine in different proportions, no fewer than four chlorides having been examined.

1. When iridium in fine powder is mixed with chloride of potassium, and the mixture heated to incipient redness in a stream of chlorine gas, part of the iridium enters into combination. The saline mass is separated by water from the metallic iridium, and aqua regia being added to the liquid, it is evaporated to dryness. The excess of chloride of potassium may be washed out with a little water. The salt may then be dissolved in boiling water containing a little aqua regia, and crystallized. Black octahedrons are obtained, composed of one atom chloride of potassium and one atom bichloride of iridium. It is therefore a bichloro-iridiate of potassium. The bichloride of iridium has not been obtained in a separate state, but it is obviously a compound of
[table]

2. Sesquichloride of iridium may be obtained by heating iridium with a mixture of potash and nitre, and, after having washed it with boiling water, digesting the remaining mass in muriatic acid, which dissolves a great deal of the matter, and assumes a blackish-brown colour. Evaporate the solution to dryness, and digest the dry residue in alcohol, which dissolves the sesquichloride. The salt dissolved may be considered as a compound of one atom sesquichloride of iridium, and one atom of chloride of potassium. The sesquichloride is a compound of
[table]

3. When iridium, obtained by reducing the double chlorides by means of a stream of hydrogen gas, is exposed at an incipient red heat to a stream of chlorine gas, it swells up, and is converted into a light powder of an olive-green colour. The additional weight corresponds with an atom of chlorine. Hence the chloride is a compound of
[table]

4. Terchloride of iridium has been obtained in combination with chloride of potassium. When ore of iridium, after fusion with nitre, has been treated with aqua regia, and then dried, small quantities of water, cautiously added, dissolve out the excess of the chloride of potassium; after this, water digested on it acquires a red colour. Dissolve off as much as can be done by repeated additions of water as long as the colour continues red. Eraporate the red-coloured solutions to dryness, and the dry mass being digested in alcohol of 0 ’ 84 to dissolve out the excess of chloride of potassium, a saline brown powder remains, which is a terchloro-iridiate of potassium. The terchloride which it contains is a compound of
[table]

The other compounds of iridium and the simple substances are still unknown. With gold and silver it forms malleable alloys, and cannot be separated from the metals by cupellation. With lead, copper, and tin, it forms malleable alloys. With arsenic it does not seem to combine.
[7:6:425]

Sect. VI.— Of Osmium.

This metal is always found combined with iridium. The method of separating it from the black powder which remains undissolved when the crude ore of platinum is digested in aqua regia, has been stated at the beginning of the last section. When the alkaline solution of osmium is mixed with muriatic or nitric acid and distilled, oxide of osmium passes over into the receiver, dissolved in water. To obtain the osmium from this liquid, agitate a quantity of mercury in it, after having added as much muriatic acid as is capable of converting the mercury into chloride. Most of the osmium forms an amalgam with the mercury, but a little still remains in solution. To obtain it, saturate the liquid with ammonia, evaporate the whole, to dryness, and beat the dry mass in a retort. Metallic osmium remains, while the mercury and sal ammoniac sublime. The chloride of mercury, amalgam of osmium and running mercury from this process, is to be heated in a glass tube, while a current of hydrogen gas is made to pass over it. Mercury and chloride of mercury sublime, and metallic osmium remains. It has the form of a black powder, which acquires the metallic lustre when burnished.

Osmium has a strong metallic lustre and a white colour, similar to that of ore of iridium. Its specific gravity is ten. It dissolves slowly in nitric acid. In aqua regia it dissolves rapidly, and so does it in fuming nitric acid when assisted by heat. When in a state of great division, it takes fire, and burns at a red heat. The metal is not altered by exposure to the air at common temperatures. Having been obtained only in the state of powder, we do not know whether it be a malleable or brittle metal.

I. It is capable of combining with various proportions of oxygen, though the number of its oxides has not yet been determined with accuracy.

1. The protoxide may be obtained by treating the eliloro-osmiate of potassium with caustic potash. In a few hours the hydrated protoxide is deposited, of a deep-green colour, almost hlack. It dissolves slowly in acids, communicating a blackish-green colour, like the salts of iridium. Nitric acid dissolves it without the application of heat, and when evaporated to dryness leaves a green-coloured transparent varnish. The sulphate becomes almost black when dried. Muriatic acid dissolves it, and assumes a deep greenish-brown colour. It detonates with combustibles. It is a compound of
[table]

2, The existence of a sesquioxide of osmium has been conjectured, but it has not been obtained in a separate state.

3. Binoxide of osmium may be obtained by treating bichloro-osmiate of potassium with carbonate of soda. After some time the liquid becomes muddy and black, and allows the hydrated binoxide of osmium to fall. When collceted on the filter it is black, and contains alkali, which cannot be removed by washing. After exposure to a red heat it ceases to be soluble in acids, though its composition is not changed. It is a compound of
[table]

4. The volatile oxide which comes over dissolved in water in the process described at the beginning of this section, appears to be a quatcroxide. It is obtained when osmium is burnt, or when we treat oxide of osmium with nitric acid. When pure it is white, with a slight tint of yellow, and may be obtained in crystals. It dissolves slowly in water, and forms a colourless solution. It dissolves also in alcohol and ether, but' is gradually reduced and deposited in the metallic state. This oxide has a strong and peculiar smell. It is a compound of
[table]

When gallic acid is dropt into the aqueous solution of quateroxide of osmium, the liquid gradually assumes a deep-blue colour. This colour is owing to the formation of a blue oxide of osmium, the constitution of which has not yet been determined.

II. The number of chlorides of osmium is fully as great as that of the oxides.

1. When chlorine gas is passed over osmium at the ordinary temperature of the atmosphere, there is no apparent action; but if we heat the metal, there instantly rises from it a dark-green sublimate, which is cldoride of osmium. If we continue the passage of chlorine gas and the heat, a red pulverulent sublimate gradually makes its appearance, which is the bichloride of osmium. If the chlorine gas be moist the bichloride becomes yellow, and gradually crystallizes. When the bichloride is dissolved in water, it assumes a yellow colour; on adding a new portion of water the colour changes to green, and the smell of the volatile oxide becomes apparent.

2. The sesquichloride and terchloride have not been obtained in a separate state, but they have been formed in combination with chloride of potassium.

III. Osmium has a strong affinity for sulphur, and forms as many sulphurets as it does chlorides. -Sulphuretted hydrogen throws it down from all its solutions, and the nature of the sulphuret formed depends upon the state of the osmium before its decomposition.

The remaining combinations into which osmium enters have not yet been investigated.

DIVISION. II.— OF PRIMARY COMPOUNDS.

Having finished the history of the simple substances, we now proceed to give an account of the compounds which they form with each other. By primary compound is meant a combination of two or more simple bodies with each other. Thus potash is a primary compound, being composed of potassium and oxygen united together. Cyanogen is another of these compounds, being composed of carbon and azote united in definite proportions. Almost all of these primary compounds have been noticed in the last division of this article; but we must here treat of the most important of them in greater detail than could be done with propriety while treating of the simple substances, and give an account of several important bodies which were of necessity omitted. Now all the primary compounds naturally divide themselves into three classes; namely, acids, alkalies or bases, and neutrals. These three classes will be treated in succession in the three following chapters.

CHAP. I.—OF ACIDS.

By acid is understood, in the present language of chemists, a substance which has the property of combining with and neutralizing alkalies or bases, Formerly it was considered as requisite that bodies, in order to belong to the class of acids, should have a sour taste, should be soluble in water, and should have the property of reddening vegetable blues; and these properties do indeed belong to some of the most common and powerful acids. But there [7:6:426] are various acids that have no taste, and which are not sensibly soluble in water, and some which are not capable of altering the colour of the most delicate vegetable blues. All the acids with which we are acquainted are compounds. Lavoisier was of opinion that oxygen constituted an essential constituent of them all; and this opinion holds good with the greater number of acids hitherto examined by chemists. But it is now known that not only oxygen, but all the other simple supporters, namely, chlorine, bromine, iodine, and fluorine, are capable of forming acids by uniting with several of the acidifiable bases, and indeed also when they unite with several of the alkaline bases, especially those described under the name of noble metals. Besides the supporters, cyanogen, sulphur, selenium, and tellurium, have also the property of forming acids when they unite with the acidifiable bases. Indeed it is not improbable that this property will be ultimately found to belong to the greater number, if not the whole of the acidifiable bases. Thus the acids at present known may be divided into nine classes, namely,
Oxygen acids.
Chlorine acids.
Bromine acids.
Iodine acids.
Fluorine acids.
Cyanogen acids.
Sulphur acids.
Selenium acids.
Tellurium acids.

Let us take a view of each of these nine classes in succession.

CLASS. I.—OXYGEN ACIDS.

The acids which contain oxygen as an essential constituent have been longer known and more carefully studied than those which belong to the other eight classes. This is the reason why at present they are so much more numerous than all the other acids put together. The oxygen acids are of two kinds. Some consist of oxygen united to a single base or a single supporter. Thus sulphuric acid is a compound of sulphur and oxygen, and carbonic acid of carbon and oxygen. But there are a considerable number of oxygen acids, in which the oxygen is united at once with two, and sometimes with three bases. Thus acetic acid is a compound of oxygen, carbon, and hydrogen, while uric acid is a compound of oxygen, carbon, hydrogen, and azote. This second set of acids is very numerous. They either exist ready formed in the vegetable or animal kingdom, or they are formed from vegetable and animal bodies by certain chemical processes. Thus the oxygen acids require to be subdivided into two sets, namely,

1. Acids with a simple base.

2. Acids with a compound base.

The first of these divisions includes the most important of those acids that are employed as instruments of chemical investigation, yet there are several acids with a compound base that can scarcely be dispensed with in a che-jnical laboratory.

Set 1. Acids with a Simple Base.

The oxygen acids with a simple base, so far as we are at present acquainted with them, amount to thirty-six. Their names are as follows:

1. Perchloric.

2. Chloric.

3. Chlorous?.

4. Bromic.

5. Iodic. .

6. Nitric.

7. Nitrous.

8. Hyponitrous.

9. Carbonic.

10. Oxalic. .

11. Boracic.

12. Silicic.

13. Phosphoric

14. Pyrophosphoric.

15. Phosphorous

16. Hypophosphorous.

17. Sulphuric.

18. Sulphurous.

19. Hyposulphurous.

20. Hyposulphuric

21. Subsulphurous.

22. Selenic.

23. Selenious.

24. Telluric.

25. Arsenic.

26. Arsenious.

27. Antimonic.

28. Antimonious.

29. Chromic.

30. Uranic.

31. Molybdic.

32. Tungstic.

33. Columbic.

34. Titanic.

35. Manganesious.

36. Manganesic.

An account of the nature and properties of all these acids has been given in the preceding part of this article, while treating of the simple substances which constitute the bases of these acids. We therefore refer the reader for information to that part of the article.

Set 2. Oxygen Acids with a Compound Base.

The oxygen acids with a compound base are very numerous, and are daily augmenting as chemists extend their researches into the animal and vegetable kingdoms of nature. The double base consists most frequently of carbon and hydrogen, sometimes of carbon, hydrogen, and azote; and there are a few of them into which sulphur enters likewise as a constituent.

Many of these acids exist ready formed in the vegetable kingdom; some are formed by a species of fermentation, to which vegetable substances are liable; others are formed during the distillation of certain bodies; and nitric acid, and even sulphuric acid, have the property of converting various vegetable and animal bodies into acids.

We shall, in the first place, give a list of all the compound oxygen acids at present known, and then make a few remarks upon the most remarkable and important of them. Those who wish to be acquainted with every thing that is at present known respecting acids will find the subject treated of at considerable length in the second volume of Dr Thomson’s System of Inorganic Chemistry (seventh edition), just published.

A. Acids composed of Oxygen united to Carbon and Hydrogen.

1. Acetic.

2. Lactic.

3. Caseic.

4. Fibric.

5. Formic.

6. Mellitic.

7. Tartaric.

8. Racemic.

9. Citric.

10. Pyrocitric.

11. Malic.

12. Pyromalic.

13. Fungic.

14. Igasuric.

15. Laccic.

16. Solanic.

17. Mucic.

18. Pyromucic.

19. Succinic.

20. Benzoic.

21. Croconic.

22. Gallic.

23. Ellagic.

24. Ulmic.

25. Crameric.

26. Kinic.

27. Pyrokinic.

28. Meconic.

29. Boletic.

30. Camphoric.

31. Suberic.

32. Pectic.

B. Fatty Acids composed of the same ingredients.

I. — Solid.

1. Stearic.

2. Margaric.

3. Capric

4. Ricinic. .

5. Cevadic.

II. — Liquid.

6. Oleic.

7. Phocenic.

8. Butyric.

9. Caproic.

10. Hircic

11. Elaiodic.

12. Crotonic

III.— Not soapifiable.

13. Ambreic.

14. Cholesteric.

C. Resinous Acids composed of the same ingredients.

1. Pinic.

2. Silvic.
[7:6:427]

D. Acids composed of Oxygen, Carbon, and Azote.

1. Carbazotic.

2. Indigotic.

3. Uric.

E. Acids composed of Oxygen, Hydrogen, Carbon, and Azote.

1. Aspartic.

2. Nitrosaccharic.

3. Nitroleucic.

4. Pyruric.

5. Purpuric.

6. Allantoic.

F. Acids composed of Oxygen, Hydrogen, Carbon, and Sulphur.

1. Hydro-carbo-sulphuric

2. Theiovinic. .

3. Xanthic.

4. Theio-naphthalic.

5. Vegeto-sulphuric

We see from the preceding list, that the compound oxygen acids at present known amount to sixty-two. Many of these, however, have been but superficially examined, and are so scarce that it has not been possible hitherto to apply them to any useful purpose; while others are abundant, and possess qualities that render them precious in the arts, or indispensable in the laboratory of the practical chemist. We shall satisfy ourselves here with a few observations on the most important.

1. Acetic acid, or vinegar (as it is called in common language), is a well-known liquid, formed during a peculiar fermentation, to which wine and beer are liable when kept in a high temperature, while at the same time air has access to them. They become sour, and all (or almost alD the alcohol which they previously contained disappears. For the full development of the acetic acid in these liquids, a temperature of about 84° is requisite. The beer to be converted into vinegar is put into stoves kept at that temperature, placed in casks with their bungs out. When the vinegar thus made is distilled at a low temperature, a transparent colourless liquid passes over called distilled vinegar or acetous acid. When this distilled vinegar is saturated with soda or its earbonate, and the solution evaporated to dryness, a white transparent salt is obtained called acetate of soda. This salt may be rendered anhydrous by exposure to a temperature of about 500°. If ten parts and a quarter of this anhydrous salt be mixed in a retort with six and an eighth parts of concentrated sulphuric acid of commerce, and heat applied, there passes into the receiver a very strong acetic acid, having an exceedingly pungent smell, similar to that of vinegar, but so strong as to be too powerful for the organs of smell. Its action upon the skin is so strong that it is capable of inflaming and even blistering any part of the body to which it may be applied. The acid, when of this strength, is liquid during summer, but whenever the temperature sinks below 40°, it congeals or crystallizes. It is a compound of
[table]

The acetic acid cannot be deprived of this proportion of water unless by combining it with some other substance. In an isolated state it is not capable of existing. Its specific gravity at 60° is 1∙06296. When diluted with water it becomes heavier, and its specific gravity is a maximum. When the liquid is a compound of
[table]

it is then 1∙07T32.

When acetic acid is exposed to a strong red heat, as by passing it through a narrow porcelain tube in a state of ignition, it is decomposed; but this does not happen unless the temperature be very high. If we fill the tube with pieces of charcoal, the decomposition is complete at a much lower temperature.

Acetic acid combines with all the bases, and forms a set of salts, to which the name of acetates has been given. All the acetates, without exception, so far as we know at present, are soluble in water. One of the most insoluble of them all is the acctated suboxide of mercury. It crystallizes in silvery plates, and requires about 600 times its weight of water to dissolve it. The acetate of silver is also very little soluble, requiring about 100 times its weight of water to dissolve it. Several of the acetates are deliquescent. This is the case with the acetate of potash. The acetate of ammonia is very deliquescent, and so volatile that it cannot, without particular contrivances, be obtained in crystals. Some acetates lose a portion of their acid by keeping. This is the case with the acetate of zinc.

Acetic acid has been analysed by mixing a quantity of an anhydrous acetate with black oxide of copper, and heating it to incipient ignition. The acetic acid is decomposed, and, combining with the oxygen of the black oxide, is converted into water and earbonic acid. The water is collected in a tube filled with chloride of calcium, the weight of which has been previously determined; while the earbonic acid is collected in a glass jar standing inverted over mercury in a mercurial trough. By determining the weight of water formed, and the quantity of carbonic acid evolved, the proportion of hydrogen and carbon in the acetic acid employed is ascertained. What is wanting to complete the weight of the acetic acid is considered as oxygen. In this way the constituents of acetic acid have been found
[table]

Thus making the atomic weight of the acid 6∙25. And this, in fact, agrees with the weight of acid necessary to saturate an atomic proportion of the bases.

2. Lactic acid is the acid formed when milk is allowed to become sour. It is formed also during a kind of fermentation which starch (especially oatmeaD undergoes when kept dissolved, or mixed with water. The characters of this acid approach those of acetic acid so nearly, that many chemists have been induced to consider them as the same. However, there are several remarkable differences between them. Lactic acid is not nearly so volatile as acetic, and its smell is quite different, and not nearly so agreeable. The salts of laetic acid, like the acetates, are all soluble; but hitherto they have been but superficially examined.

3. Caseic acid is a name which has been given to the acid formed when the curd of milk is exposed to the putrefactive fermentation. It is a yellow, syrupy liquid, which seems to owe its acid properties to a quantity of acetic acid which it contains, and which had been formed during the putrefaction of the curd

4. Fγbric acid was extracted in crystals from the fresh muscle of an animal, by digesting it in cold water, evaporating the liquid to the consistence of a syrup, and mixing the syrup with strong alcohol After some days standing in a close vessel, the alcohol deposits needle-formed crystals, which have acid properties; but their nature has not been accurately ascertained.

5. Formic acid may be obtained by digesting the formica rufa, or red ant, in hot water. Döbereiner discovered that if we mix together in a large retort one part of crystals of tartaric acid, two and a half parts of deutoxide of manganese, and two and a half parts of concentrated[7:6:428] sulphuric acid, previously diluted with twice its weight of water, and apply heat, much carbonic acid is disengaged, and the matter in the retort swells and has a great tendency to run over. After the disengagement of gas is at an end, if we distil over the liquid, we obtain dilute formic acid. This process succeeds equally well if we substitute starch for tartaric acid.

This acid has a strong resemblance to the acetic; but the differences are also decided. It cannot be made to crystallize, its specific gravity is higher, and the salts which it forms have different properties. When mixed with concentrated sulphuric acid, it is converted into water and carbonic oxide. Its constituents are,
[table]

So that it differs from acetic acid by containing only half the quantity of carbon and hydrogen that exist in that acid. Were we to suppose the carbon and hydrogen in these acids to be combined together, and to constitute a base, to which the oxygen afterwards united in order to convert it into an acid, the base of acetic acid would be a compound of
[table]

while the base of formic acid would be
[table]

The ratio of the carbon is the same in both, but the absolute quantity is double in acetic acid to what it is in formic acid.

6. Mellitic acid existá as one of the constituents of a honey-yellow mineral, crystallized in octahedrons, found among the layers of wood-coal in Thuringia, and called from its colour mellite. This mineral is a compound of mellitic acid and alumina. Mellitic acid has a very strong resemblance to oxalic acid, and, like it, is not liable to decomposition when kept in solution in water. Its atomic weight is 6∙5, but it has not yet been subjected to an analysis to determine its constituents.

7. Tartaric acid is one of the constituents of cream of tartar, a salt which encrusts the sides and bottoms of winceasks, being gradually deposited from the wine. This salt is now called bitartrate of potash, being a compound of
[table]

This salt is decomposed by lime, which separates the tartaric acid from potash, forming with it an insoluble and tasteless white powder. Sulphuric acid, when digested over this powder, gradually combines with the lime, and sets the tartaric acid at liberty. It dissolves in the water, and may be obtained in crystals by concentrating the liquid. This acid is prepared in large quantities for the calico-printers, who employ it to discharge the turkey-red dye by means of bleaching powder. It has a very sour taste, and is very soluble in water. The aqueous solution, when kept, becomes full of mucus, and the acid is gradually destroyed. It has the property of combining in two proportions with most bases, forming tartrates and bitartrates. The bitartrate of potash is very little soluble in water. Hence if we drop carbonate of potash by degrees into a solution of tartaric acid, a copious precipitate of small acidulous crystals gradually falls down. This precipitation is characteristic of tartaric acid. Carbonate of soda cannot be substituted for potash, because the bitartrate of soda is much more soluble in water than bitartrate of potash. When tartaric acid is added to a solution of a metal in an acid, it in general prevents the metallic oxide from being thrown down by an alkali. This it does by forming with the metallic oxide a soluble double salt. The atomic weight of tartaric acid is 8∙25, and the crystals are composed of
[table]

The acid itself has been analysed by means of oxide of copper, and found composed of
[table]

The absolute quantity of carbon and hydrogen is the same as in acetic acid; but the oxygen, instead of three atoms, as in acetic acid, is five atoms. The properties of the two acids are exceedingly different.

8. RacExMic acid is an acid that has been recently found in cream of tartar. It therefore exists as a constituent of the juice of grapes, and appears in the fruit to be in a state of biracemate of potash. It may be separated and purified precisely in the same way as tartaric acid. The Germans (for it was first noticed in Germany) have given it the name of traubensaure (grape acid). This appellation not being suitable to the idiom of the English language, the French chemists who first described it gave it the name of racemic, acid. It crystallizes in doubly oblique prisms, the lateral faces of which are inclined to each other at angles of 68° and 112°, and the inclination of the base to the lateral faces is about 75°. It resembles tartaric acid in many of its properties; but it precipitates lime from a solution of chloride of calcium, which is not the case with tartaric acid. The salts also which it forms differ from those of tartaric acid. Its constitution and atomic weight, according to Berzelius, are precisely the same as those of tartaric acid. The crystals are composed of
[table]

It is a stronger acid than tartaric. When heated with sulphuric acid and deutoxide of manganese, it gives out much carbonic acid and some acetic acid, but no formic acid, as is the case when tartaric acid is treated in the same way.

9. Pyrotartaric acid is an acidulous liquor, obtained by distilling bitartrate of potash in a retort. It is exceedingly sour tasted, and may be crystallized. It neither precipitates lead nor silver, which readily distinguishes it from tartaric acid.

10. Citric acid is extracted from the juice of limes and' lemons, by saturating the filtered juice with lime, and decomposing the insoluble citrate of Jime obtained by means of dilute sulphuric acid. It is readily obtained in crystals, which have the form of right rhombic prisms, and are composed of
[table]

The salts which it forms are called citrates. It is a weaker acid than tartaric, and is easily decomposed by heat. By [7:6:429] heating it with oxide of copper its constituents have been found to be
[table]

The absolute quantity of carbon and hydrogen is the same as in acetic and tartaric acids; but the oxygen amounts only to four atoms, while it is five in tartaric acid and three in acetic.

11. Pyrocitric acid is obtained by distilling crystallized citric acid in a retort. It has an acid and bitterish taste, and crystallizes, though not regularly. It forms the salts called pyrocitrates. The atomic weight of this acid is 10∙75, and it is said to be a compound of
[table]

These atomic constituents differ very much from those of citric acid.

12. Malic acid exists in the juice of apples, and of the mountain-ash. It may be crystallized, though not without difficulty; and it is a much weaker acid than even the citric. Most of the salts which it forms are soluble in water. They are called malates. The atomic weight of this acid appears to be 9Ό625, and it is a compound of
[table]

But the characters of the acid have not been well defined, and at least two different acids seem to have been confounded under the same name.

13. Fungic acid exists in the juice of the peziza nigra, and various other fungi.

14. Igasuric acid exists in St Ignatius’ bean, the fruit of the strychnos ignatia.

15. Laccic acid was obtained from stick lac.

16. Solanic acid from the berries of the solanum nigrum.

17. Pyromalic acid is formed when malic acid is distilled in a retort. It is volatilized under the form of white needles.

. 18. Mucic acid, or saclactic acid, is formed when gum or sugar of milk is digested in nitric acid. On allowing the liquid to cool after the effervescence is over, the mucic acid is deposited in very small crystals, constituting a white powder. It has a sour taste, is but little soluble in water, and constitutes a set of salts called mu-cαtβs when it is combined with bases. Its atomic weight is 13, and it is a compound of
[table]

19. Pyromucic acid is obtained by distilling mucic acid in a retort. It is in crystals, which are more soluble in alcohol than water, and which are not altered by exposure to the atmosphere. Its atomic weight is the same with that of mucic acid, but its constituents are,
[table]

20. Succinic acid is obtained by distilling amber. It forms large, transparent, colourless crystals, which are but little soluble in water. The salts which it forms are called succinates. This acid, when heated, sublimes without decomposition. Succinate of ammonia, or of soda, has the property of precipitating peroxide of iron from neutral solutions. Hence these salts are employed to separate iron from manganese. The component parts and atomic weight of this acid are the same as those of acetic acid, namely,
[table]

21. Benzoic acid sublimes when the resinous substance called benzoin is heated. It constitutes beautiful snow-white elastic needles, exceedingly light, and consequently very bulky. It is but little soluble in water. It combines readily with bases, and constitutes the salts called benzoates. Like succinic acid, it is often employed to separate iron from manganese, because it precipitates peroxide of iron from neutral solutions without acting on manganese. Its atomic weight is 15, and its constituents are,
[table]

22. Croconic acid is a yellow-coloured acid, solid, but not in crystals, which is formed when cream of tartar previously charred in a crucible is exposed to a white heat. Potassium comes over, and among other products there is a quantity of croconate of potash. According to L. Gmelin, the discoverer of this acid, it is a compound of
[table]

23. Gallic acid is obtained from nut-galls by digesting them in water, and allowing the infusion to remain for some months covered with paper. The acid is deposited in yellow crystals, which may be rendered colourless by dissolving them in boiling water, mixing the solution with ivory black, filtering, and then crystallizing. Its taste is bitter, leaving an impression of sweetness. It dissolves in about twelve times its weight of water. Its characteristic property is the deep-blue colour which it strikes when put into a solution containing peroxide of iron. Its constituents would appear to be
[table]

24. Ellagic acid is a name given by Braconnot to a white substance which remains on the filter when the impure first crystals of gallic acid are dissolved in water and filtered.

25. Ulmic acid exists in the bark of most trees, and in combination with potash it constitutes the principal part of a black exudation from ulcers which are apt to form in the elm and some other trees. By dissolving this matter in water, and adding an acid to the solution, the ulmic acid falls down in tasteless brown flocks. It combines with the different bases, and forms a class of salts called ulmates i very few of which have hitherto been examined.
[7:6:430]

Its atomic weight is 42, and it appears by Boullay’s analysis to be composed of
[table]

26. Crameric acid has been extracted from the root of the crameria triandxa.

. 27. Kinic acid exists in small quantity, united to lime, in the yellow Peruvian bark. Its atomic weight seems to be 23, and it is probably a compound of
[table]

28. Pyrokinic acid is formed when kinic acid is distilled in a retort.

29. Meconic acid exists in opium, and is characterized by striking a red with peroxide of iron solutions.

30. Boletic acid was extracted by Braconnot from the boletus pseiulo-igniarius.

: 31. Camphoric acid is formed when nitric acid in great quantity is distilled off camphor. It may be sublimed unaltered. It is but little soluble in water, but very soluble in alcohol. Its atomic weight is 14, and it is composed of
[table]

32. Suberic acid is formed when common cork is digested in a great deal of nitric acid. It is white, does not crystallize, is but little soluble in cold water, but very soluble in boiling water. It is also very soluble in alcohol. Its atomic weight seems to be 12∙5, and its constituents
[table]

33. Pectic acid exists in most vegetable bodies, and is characterized by the property which it has of forming a jelly. Currant-jelly, apple-jelly, and all the numerous tribe of vegetable jellies, owe their form to the presence of this substance. Its atomic weight appears to be about 33.

34. Stearic acid is extracted from mutton suet soap, and Margaric acid from a soap made of olive oil and potash by simple decomposition. Oleic acid is extracted from the soap of linseed oil and potash; Phocenic acid from a soap made of porpoise oil and potash; Butyric acid from a soap of butter and potash. The same soap contains also Caproic and Capric acids, while Hircic acid is extracted from a soap made of mutton tallow and potash. Ricinic and Elaiodic acids are formed during the distillation of castor oil.

Cevadic acid exists in the seeds of the veratrum sabadilla, and Crotonic acid in the fruit of the croton tiglium. It is to the presence of this acid that croton oil owes its cathartic properties.

Ambreic acid is formed when ambergris is digested with a sufficient quantity of nitric acid. The same process enables us to form Cholesteric acid from cholcs-terine, a crystallized substance that constitutes the most common kind of biliary calculi.

Pinic acid is the resin which exudes from the pinus abies, and Silvic acid the resin which exudes from the pinus silvestris.

35. Carbazotic acid is obtained by digesting good indigo in about ten times its weight of nitric acid, till all ’ effervescence is at an end. It is deposited in yellow semitransparent crystals, which may be purified by repeated crystallizations. It is crystallized in fine plates, having a silky lustre and a yellow colour.» When heated it melts, and may be volatilized without decomposition. It is little soluble in cold, but very soluble in hot water. It is soluble also in alcohol and ether. It is a strong acid, and the salts which it forms detonate when heated. It is said to be a compound of
[table]

36. Indigotic acid is obtained by adding powdered indigo by little and little to a boiling hot but very weak nitric acid, continuing to add the indigo as long as any effervescence lasts. The liquid thus formed is to be separated while hot from the resinous matter deposited. On cooling, it lets fall indigotic acid in very small crystals. These crystals when purified are white, very bulky while moist, but they diminish much and lose their crystalline form when dried. They have a silky lustre. The acid is very little soluble in water. It melts when heated, and sublimes without decomposition. It gives a blood-red colour to solutions of peroxide of iron. Its atomic weight seems to be 35, and its constituents to be
[table]

37. Uric acid exists in small quantities in healthy human urine, and constitutes the principal constituent of the most common kind of urinary calculi. The excrements of the boa constrictor consist almost entirely of this acid. It is white, tasteless, and may be obtained in very small prisms, having somewhat of a silky lustre. It dissolves in nitric acid with effervescence, and when the solution is evaporated to dryness a most beautiful pinkcoloured sediment remains behind. It combines with the different bases, and forms the salts called urates, most of which are white, tasteless, insoluble powders. The crystals of uric acid are composed of
[table]

Uric acid itself is composed of
[table]

28. Pyruric acid is the yellow-white sublimate which rises when uric acid is subjected to distillation. When pure it is in white small needles, which feel somewhat gritty between the teeth. It is slightly soluble in water. Concentrated nitric acid dissolves it, but by evaporation the pyruric acid may be again obtain unaltered. Its atomic weight is probably 11, and its constituents
[table]
[7:6:431]

39. Aspartic acid was obtained from the juice of the young shoots of asparagus. All the aspartates have a flavour analogous to that of beef tea. When the acid is decomposed by heat, it gives out ammonia and cyanogen. It is obvious from this that carbon, hydrogen, and azote exist in it as constituents, doubtless combined with oxygen; but no satisfactory analysis of it has been hitherto made.

40. Nitrosaccharic acid was obtained by Braconnot by the following process: Strong glue was boiled with its own weight of sulphuric acid, previously diluted with water for five hours; and the acid being saturated with lime, and the whole filtered, the liquid in about a month deposited sugar of glue. This sugar dissolves in hot nitric acid without effervescence. By cautious evaporation a white crystalline mass is obtained, which is nitrosaccharic acid. It is very soluble in water, and crystallizes in flat, striated, transparent prisms. Its taste is acid, and slightly sweet. It combines with bases, and forms salts called nitrosaccharates. It would seem to be a combination of nitric acid and sugar of glue.

41. Nitroleucic acid was obtained by nearly a similar process. Muscle of beef was boiled for five hours with its weight of sulphuric acid previously diluted with water. The acid being separated by lime, a white substance was obtained, not in the least sweet, but having the flavour of boiled meat. To this substance Braconnot, who formed it, has given the name of leucine. It dissolves readily in nitric acid without effervescence, and by cautious evaporation nitroleucic acid is obtained in a crystalline mass. It forms peculiar salts when combined with the different bases, and seems to be a compound of nitric acid and leucine.

42. Purpuric acid was formed by Dr Prout by dissolving uric acid in nitric acid, saturating the solution with ammonia, and evaporating cautiously. Red crystals speedily fell. They were dissolved in a solution of caustic potash, and this solution being poured into sulphuric acid, the purpuric acid precipitated in the state of a cream-coloured powder. It has no smell or taste, and is but very little soluble in water. In alcohol and ether it is quite insoluble. It combines with bases, and forms salts, the greater number of which have a red colour. Its constituents are,
[table]

so that its atomic weight is 5∙5, or a multiple of that number.

43. Allantoic acid is the name of the acid which Vauquelin and Buniva called amniotic, because it is found in the liquor of the allantois, and not in that of the amnios. It crystallizes in square prisms, has a white colour and pearly lustre, is insipid, and not altered by exposure to the air. It is very little soluble in water, more soluble in alcohol, but a portion of it is deposited in crystals as the solution cools. The allantates are all soluble in water, and crystallizable. The atomic weight of this acid is about 62, and its constituents seem to be
[table]

44. Hydro-carbo-sulphuric acid was obtained by mixing bisulphuret of carbon with an alcoholic solution of ammonia. Feather-shaped crystals are deposited. These being cleaned by means of bloating paper dissolved in water, and the solution mixed with dilute muriatic acid, an oily liquid separates, which is hydro-carbo-sulphuric acid. Zeise, the discoverer of this acid, considers it a combination of one atom hydrogen with an atom of a compound of sulphur and carbon, which he calls xanthine i and which he is of opinion is a compound of
[table]

so that the atomic weight of the acid is 6∙875; or we may consider the acid as a compound of
[table]

45. Theiovinic acid is formed when sulphuric acid and alcohol are digested together for some time. The liquid is then saturated with carbonate of lead, filtered, and a current of sulphuretted hydrogen gas passed through the liquid to throw down the lead. The liquid, thus containing sulphovinic acid, may be concentrated by being exposed in a vacuum over sulphuric acid till its specific gravity amount to 1*319. When raised to the boiling point, or when concentrated beyond l∙319, it is decomposed, sulphurous acid escaping, and sulphuric acid remaining mixed with an ethereal oil. It has been shown by Mr Hennell to be a compound of
[table]

46. Xanthic acid is formed when bisulphide of carbon is left in contact with an alcoholic solution of potash. Needle-shaped crystals are deposited. When these crystals are mixed with dilute muriatic acid, xanthic acid separates under the form of a liquid like oil. Zeise, the discoverer of this acid, is of opinion that it is a compound of
[table]

47. TiiEioNΛPiιτ∏ALic acid is formed by leaving concentrated sulphuric acid in contact with naphthaline. It seems to be a compound of
[table]

48. Vegeto-sulpnuric acid was formed by Braconnot in the following way: Pieces of linen or hemp cloth were left in contact with concentrated sulphuric acid. They were converted into a pulp. This pulp being diluted with water, a great deal of it dissolves, leaving a black matter. Filter, saturate the solution with carbonate of lead, filter again, and precipitate the lead from the solution by a current of sulphuretted hydrogen. The liquid, thus freed from lead, when cautiously concentrated, leaves a transparent substance like gum arabic. This gum being boiled for some time in very dilute sulphuric acid, is partly converted into a crystallizable sugar, and partly into the acid called vegeto-sulphuric. It may be separated from the sugar by digestion in rectified spirits, evaporating to the consistence of a syrup, and digesting the syrup in ether. The pure acid only is dissolved, and may be obtained in a separate state by evaporating off the ether. It is a strong, colourless acid, decomposed by boiling, and [7:6:432] then exhibits the presence of sulphuric acid. It forms soluble salts with all the bases. It is probably a compound of sulphuric acid and the sugar of linen.

CLASS II.—CHLORINE ACIDS.

No doubt the acids formed by the combination of chlorine with bases will one day rival in number the oxygen acids themselves; but the investigation of them is hardly yet begun. The consequence is, that scarcely any of them except muriatic acid, which is a combination of hydrogen and chlorine, has been hitherto investigated with care. The nature and properties of this acid have been given in this article while treating of hydrogen, to which we refer the reader.

The chlorides of sulphur and of phosphorus do not seem to possess acid properties; but corrosive sublimate possesses acid properties, and is capable of combining with and forming salts with a great number of alkaline chlorides. The chlorides of gold, platinum, palladium, rhodium, iridium, and osmium, possess also acid properties, and combine into crystallizable salts with various alkaline chlorides.

CLASS III. BROMINE ACIDS.

Bromine has bccn known for so short a time, and is still so scarce, that we need not be surprised that this class of salts is still almost unknown. Except hydrobromic acid, composed of
[table]

we are acquainted with none of the acids belonging to this class. The properties of this acid have been already given under the head of hydrogen, in a former part of this article.

CLASS IV. IODINE ACIDS.

The analogy between oxygen, chlorine, bromine, and iodine, is so great that we cannot avoid admitting that iodine, like the other supporters, has the property of forming acids when it combines with the acidifiable bases. But, excepting hydriodic acid, very few of the iodine acids have been examined. The periodide of mercury and iodide of arsenic are acids, but the salts which they form are but imperfectly known.

CLASS V. FLUORINE ACIDS.

We arc at present acquainted with eight acids, which are considered as combinations of fluorine and a base. These are,

1. Hydrofluoric acid.

2. Fluoboric.

3. Fluosilicic.

4. Fluomolybdic.

5. Fluotungstic.

6. Fluochromic.

7. Fluocolumbic

8. Fluotitanic.

1. Hydrofluoric acid was originally called fluoric acid, and under that name has been described in a former part of this article, when treating of fluorine.

2. Fluoboric acid is obtained most easily by dissolving anhydrous boracic acid in fluoric acid. A colourless gas is extricated, which may be received over mercury. An account of this acid has been given already, while treating of boron, in a preceding part of this article.

3. Fluosilicic acid is the colourless gas which is obtained when a mixture of sulphuric acid and fluor spar is heated in a glass retort. This gas has the smell of muriatic acid, and, like that acid, gas is absorbed abundantly by water, while at the same time it deposits silica in the state of a jelly. Its atomic weight appears to be 6∙5, and it seems to be a compound of
[table]

4. Fluomolybdic acid is obtained by dissolving molybdic acid in hydrofluoric acid. It has an acid, metallic, and disagreeable taste. It does not crystallize, but may be evaporated to the consistency of a syrup. It combines with bases, and forms a set of salts called fluomolybdates. There is reason to believe that this acid is a compound of
[table]

and that its atomic weight is 11∙375.

5. Fluotungstic acid is formed by dissolving tungstic acid in hydrofluoric, and it seems to be a compound of
[table]

6. Fluociiromic acid is obtained by putting equal weights of fluor spar and chromate of lead, mixed with thrice their weight of smoking sulphuric acid, into a leaden retort, and applying a gentle heat. A red-coloured gas comes over, which maybe collected in a platinum vessel over mercury. It is condensed into a liquid by exposure to a temperature of 32°. Glass instantly decomposes it. Water absorbs it and converts it into fluoric acid and chromic acid. The probability is that this gas is a compound of
[table]

We do not know whether this compound oe really entitled to the name of acid. The effect which glass and water have on it makes it difficult to subject it to the requisite trials.

7. Fluocolumbic acid is formed by dissolving columbic acid in hydrofluoric. It combines with bases, and forms salts, and seems to be a compound of
[table]

8. Fluotitanic acid is formed by dissolving titanic acid in hydrofluoric. The salts which it forms are called fluotitaniates. It seems to be a compound of
[table]

CLASS VI. CYANOGEN ACIDS.

Cyanogen is a gas which is obtained by heating prussiate of mercury, or cyanodide of mercury as it is now called, in a glass retort. It must be received over mercury. It is colourless, has a peculiar smell and a strong taste, and burns with a violet-coloured flame. It is a compound of
[table]

This substance has the property of combining with various simple bases, precisely in the way that the supporters do. With some of these it forms bodies analogous to the salts; with others, bodies possessing the properties of acids. None of its combinations hitherto observed are alkaline compounds, though it is not impossible that such may be discovered[7:6:433] hereafter. The combinations of cyanogen at present known amount to fifteen. They have been distinguished by the following names:

1. Hydrocyanic acid.

2. Cyanic acid.

3. Cyanuric acid.

4. Fulminic.

5. Chlorocyanic.

6. Perchloride of cyanogen.

7. Bromide of cyanogen.

8. Iodide of cyanogen. .

9. Hydrosulphocyanic acid.

10. Hydrosulphuretted hydrosulphocyanic acid.

11. Hydrobisulphocyanic acid

12. Disulphuret of cyanogen.

13. Seleniocyanogen.

14. Hydroferrocyanic acid.

15. Azulmic acid

We shall give as brief an accountof these important bodies (all of which are not acids) as is consistent with perspicuity.

1. Hydrocyanic acid, long known by the name of prussic acid, may be obtained by the following process: Fuse the yellow-coloured salt usually known by the name of prussiate of potash, or ferruginous prussiate of potash, in a vessel to which atmospherical air has not access. By this process the cyanodide of iron which it contains is decomposed, and an inflammable gas comes over. The iron is converted into a carburet, which may be separated by dissolving the fused salt in water. If we evaporate the filtered solution, we obtain a white salt, distinguished by the name of cyanodide of potassium. Put this cyanodide into a retort or flask slightly moistened with water, and add muriatic acid by a little at a time. The hydrocyanic acid is disengaged. Cause it to pass through a tube filled with fragments of dry chloride of calcium, and receive it into a small flask, kept as cool as possible by being surrounded with a mixture of snow and salt. Here the hydrocyanic acid condenses into a liquid.

It is a colourless liquid, having a strong smell similar to that of peach blossoms. Its taste is sharp, at first it appears cooling, but it soon excites a burning sensation in the mouth. It is very asthenic, indeed a virulent poison. At 64° its specific gravity is 0∙6969. It boils when heated to 79° ∙7, and congeals when cooled down to 5°. At 80° it assumes the gaseous form. Its specific gravity is 0∙9375, and it is a compound of one volume cyanogen gas and one volume hydrogen gas united together, without any condensation whatever: hence its specific gravity is the mean of that of its two constituents.

This acid cannot be kept. It speedily undergoes spontaneous decomposition, even when kept in the dark and in a cool place. This seems to be owing to its containing muriatic acid. It is one of the most virulent poisons known. A single drop of it applied to the eye of a middle-sized dog occasions violent convulsions, terminated speedily by death. Ammonia in some measure counteracts its poisonous effects; but from the experiments of Simeon it appears that chlorine constitutes a much more certain and complete antidote. Being put into the throat of the poisoned animal it speedily relieves the symptoms; and the animal, after the interval of some hours, again recovers its health. It is used in medicine, and possesses considerable efficacy as a remedy in dyspepsia. The strength of the acid usually sold by apothecaries is from one to two parts of hydrocyanic acid in ninety-nine or ninety-eight of water. Of this, eight drops in a glass of water are administered thrice a-day. When given in large doses it diminishes the frequency of the pulse, and even throws the patient into a state of lethargy, from which, however, he gradually recovers.

2. Cyanic acid may be formed by the following process: Mix anhydrous prussiate of potash with about its own weight of black oxide of manganese, and heat this mixture in a silver crucible to incipient ignition; then boil it in alcohol of the specific gravity 0∙832. As the alcoholic solution cools, it deposits crystals of cyanate of potash in small scales. Dissolve these crystals in water, and add nitrate of silver to the solution. Cyanate of silver precipitates in a white powder, which is nearly insoluble in water. Mix it with water, and pass through the solution a current of sulphuretted hydrogen gas. The silver is thrown down, and the cyanic acid remains in solution. The liquid now contains only cyanic acid. It has a sour taste. Its smell has some resemblance to that of acetic acid. In a few hours it undergoes spontaneous decomposition, being converted into carbonate of ammonia. It combines with bases and forms salts, and its atomic weight is 4∙25. It is a compound of
[table]

3. Cyanuric acid was discovered by Serullas, but its true nature was first ascertained by Wohler and Liebig. It may be formed by dissolving perchloride of cyanogen in hot water, and boiling the solution for some time. By evaporating the liquid muriatic acid is driven off, and cyanuric acid is deposited in crystals. It is a white solid, which crystallizes in brilliant transparent rhombs. When heated it sublimes, and is then deposited in fine needles. It has but little taste, yet it reddens ‘vegetable blues. Cold water dissolves little, but hot water is a better solvent of it. Its specific gravity is rather less than that of concentrated sulphuric acid. For volatilization it requires a beat rather superior to that at which mercury boils. It combines with bases, and forms a class of salts which have been called cyamirates. From the analyses of Wohler and Liebig, its constituents appear to be
[table]

4. Fulminic acid is formed when one hundred grains of mercury arc dissolved by means of heat in a measured ounce and half of nitric acid of the specific gravity 1∙3, and the solution is poured into two measured ounces of alcohol. Heat being applied to the mixture, an effervescence takes place, and a white matter in small crystals is precipitated, which is to be collected and washed on a filter. It constitutes fulminating mercury, or a compound of fulminic acid and oxide of mercury. From this powder fulminic acid may be obtained by the following process: Put fulminating mercury into a phial with a ground stopper, together with twice its weight of clean zinc filings, and about three quarters of a fluid ounce of water for every twenty grains of fulminating mercury employed. If the bottle be kept in the temperature of 80°, and occasionally agitated, the fulminating mercury is soon decomposed, and a solution of fulminate of zinc obtained. Filter this liquid into another phial, and add to it one third of its bulk of a saturated solution of barytes in water. The oxide of zinc is precipitated, and fulminate of barytes formed. To this fulminate add just the quantity of dilute sulphuric acid that is necessary to saturate the barytes. Sulphate of barytes falls, and there remains a solution of fulminic acid in water.

It is colourless and transparent. Its taste is at first sweet, which is followed by a peculiar astringency. Its smell is pungent and disagreeable. It is very poisonous; even exposure to its fumes excites headach. It is volatile. It combines with the different bases, and forms á set of salts, all of which have the curious property of fulminating when heated, or when struck with a hammer upon an anvil. We have two different analyses of this acid. Liebig and Gay-Lussac found its atomic weight 4 , 25; and it is, according to them, a compound of
[7:6:434]
[table]

that is, the very same with cyanic acid, though its properties are quite different from those of that acid. Mr Edmund Davy found its atomic weight 5∙25, and, on analysing it, obtained as its constituents
[table]

According to this determination, it differs from cyanic acid by containing half an atom of azote and one atom of hydrogen, which arc wanting in cyanic acid; while from cyanuric acid it differs by containing half an atom of azote, which is wanting in that acid.

5. Chloride of cyanogen may be obtained by the following process: Fill a bottle capable of holding sixty cubic inches with chlorine gas, and then put into it ninety grains of cyanodidc of mercury. Introduce as much water as-will reduce the cyanodide to a magma, but not dissolve it. Put the bottle into a dark place. In ten hours a double decomposition takes place. Corrosive sublimate is formed, and the cyanogen, combined with chlorine, will fill the vessel in the state of a gas. Surround the flask with a mixture of snow and salt. The gas is converted into solid crystals, which attach themselves to the inside of the flask. Absorb all the water by introducing chloride of calcium, while the flask is in the freezing mixture, and letting it remain in the flask for two or three days; then exposing it again to the freezing mixture to congeal the chloride of cyanogen, withdraw the chloride of calcium, and fill the flask with mercury previously cooled down to zero. Introduce a bent tube into the mouth of the flask, plunge the end of this tube into a mercurial trough, then heat the flask gently. The chloride of cyanogen melts and effervesces, and passes over in the state of a gas.

At zero, chloride of cyanogen is a transparent solid, which crystallizes in long needles. It liquefies when heated to 16°. At the ordinary temperature of the air it is gaseous, but the gas liquefies at 68° when subjected to the pressure of four atmospheres. Its smell is extremely offensive and deleterious. At 68° water absorbs twenty-five times its bulk of this gas, sulphuric ether about fifty times its bulk, and alcohol about a hundred times its bulk. These solutions may be kept for any length of time without undergoing decomposition. It has not been proved that it combines with bases, so that we have no evidence that it possesses the characters of an acid. It is a compound of one volume cyanogen gas and one volume chlorine gas united together without any alteration of volume. Hence the specific gravity of chloride of cyanogen in the gaseous state is 2 , 1527.

6. Perchloride of cyanogen may be obtained in the following manner: Fill a bottle capable of containing sixty-five cubic inches with dry chlorine gas, and after putting into it about fifteen grains of pure liquid hydrocyanic acid, shut up the mouth of the phial with aground stopper, and expose it to the direct rays of the sun. A solid matter gradually attaches itself to the inside of the bottle, while the colour of the chlorine disappears. Blow out the muriatic acid formed with a,pair of bellows, then introduce a little water and a few fragments of glass, in order, by agitation, to detach the solid matter from the inside of the vessel. Agitate well, then throw the whole contents into a dish. Pick out the pieces of glass, and break the white matter with a glass rod, to allow it to be washed. Wash it and dry it. Put it into a small retort, and heat it till it fuses; then distil it over into the receiver. It passes over in the state of a transparent colourless liquid, which crystallizes.

It is a very white substance, which crystallizes in needles. It has a strong and disagreeable odour, exciting tears. Its taste is sharp, but not strong. Its specific gravity is about ,1∙320. It melts at 281°, and boils at 374°. It is very little soluble in cold water, but dissolves readily in alcohol and cther. It is a very virulent poison. It is a compound of
[table]

Whether it be capable of combining with bases, has not yet been determined.

7. Bromide of cyanogen may be formed in the following manner: Put into the bottom of a long glass tube, shut at one end, two parts of cyanodide of mercury, and, surrounding the bottom of the tube with a freezing mixture, pour on the cyanodide one part of bromine. A violent action takes place, and much heat is evolved. Bromide of mercury and bromide of cyanogen are formed, which last substance crystallizes in long needles in the upper part of the tube. Adapt a small receiver to the tube, and by a gentle heat drive the bromide of cyanogen into it, where it crystallizes. The crystals are either small transparent cubes or long needles. The smell is strong and disagreeable. It is very volatile, and at 60° assumes the form of a gas. It is soluble both in water and alcohol. When mixed with a solution of caustic potash it undergoes decomposition, being converted into hydrocyanate and hydrobromate of potash. It is exceedingly poisonous, and is composed of
[table]

8. Iodide of cyanogen is obtained by triturating together in a glass mortar two parts of cyanodide of mercury and one part of iodine. The mixture is introduced into a wide-mouthed phial, and exposed to a heat gradually increased till the cyanodide of mercury begins to undergo decomposition; then the phial is to be taken up in a pair of pincers and placed under a glass jar standing inverted on a glass plate. White vapours issue rapidly from the mixture, and condense on the glass disc like flocks of cotton. When they cease the phial is to be again heated, which causes them to appear again. This is to be repeated as long as flocks appear. These white flocks constitute iodide of cyanogen. Put them into a long glass tube shut at one end and bent a little at the upper end, and plunge the bottom of the tube in boiling water. Iodide of cyanogen is sublimed pure, and deposited in the bent part of the tube.

It is white, and crystallized in long slender needles. Its smell is strong and irritating. Its taste is excessively caustic, and its specific gravity is greater than that of sulphuric acid, through which it falls rapidly. It is soluble in water and alcohol. When caustic potash is added to the solution, hydriodate and hydrocyanate of potash are formed. Nitric acid has no action on it. Sulphuric acid slowly disengages iodine. Muriatic acid immediately decomposes it. Dry sulphurous acid and dry chlorine have no action on it. It is a compound of
[table]
[7:6:435]

It is much less deleterious than either the bromide or chloride of cyanogen.

9. Hydrosulphocyanic acid was discovered by Po-rett, and called by him sulphuretted chyazic acid. It may be obtained in the following manner: Mix together by trituration equal weights of flowers of sulphur and ferro-ρrussiate of potaslι previously deprived of its water, and fuse the mixture over a spirit-lamp at a temperature approaching a red heat. When the fused mass has become cold, dissolve it in water, and drop into the solution caustic potash till the oxide of iron has been all thrown down; filter, evaporate the colourless liquid to dryness, and dissolve the dry residue in as little water as possible. Mix this solution in a glass retort with a quantity of concentrated phosphoric acid, and distil. Hydrosulphocyanic acid passes over into the receiver.

Hydrosulphocyanic acid thus obtained has a very sour taste. It is transparent and colourless, and has a strong smell, resembling that of acetic acid. It crystallizes at 14° and boils at 216į°. When the acid is thrown into a red hot platinum crucible, sulphur is disengaged, and burns at last with a blue flame. It possesses poisonous qualities, but is much less energetic than hydrocyanic acid. It combines with bases and forms salts. Its most striking property is the blood-red colour which it produces when mixed with solutions of peroxide of iron. This colour is so intense that we can by means of it detect a very minute quantity of peroxide of iron in solution. The constituents of this acid are,
[table]

There is reason to believe that the radical of this acid, called sulpliocuanoqen acid, and composed of
[table]

is capable of existing in a separate state. When the acid is decomposed by galvanism, a yellow-coloured matter makes its appearance, which seems to be this radical.

10. Hydrosulphuretted uydrosulphocyanic ACID was discovered by Zeise during his researches on the alterations to which bisulphurct of carbon is subjected under peculiar circumstances. He obtained it by the following process: Saturate alcohol with ammoniacal gas at 50°, mix it with 0 ’ 4 of its original volume of alcohol, and with 0T6 of that volume of bisulphuret of carbon. The mixture should be made in a phial which should be completely filled with it. Let the phial be well stopped, and kept at the temperature of 60°. In an hour and a half a salt falls in crystals. It is a combination of sulphuret of ammonia and bičarburet of sulphur. Filter the liquid as rapidly as possible into another phial, which must be hermetically sealed. Keep it for six hours at the temperature of 60°, then cool it to 46°, and finally plunge it into a freezing mixture of snow and salt. By this treatment another salt is obtained, which is a combination of sulphuret of ammonia with hydrosulphocyanic acid. Separate this salt, wash it with a little alcohol cooled down to 32°, and then press it between folds of blotting paper. Dissolve it in three times its weight of water, and add to the solution dilute muriatic or sulphuric acid. After sufficient mixture pour it at once into a great quantity of water. An oily-looking matter is collected at the bottom of the vessel, which is hydrosulphuretted hydrosulphocyame acid. It is colourless, but water decomposes it so rapidly that it has been impossible to examine its properties. It is a compound of
[table]

For, when placed in contact with a metallic oxide, the oxide is immediately reduced to a sulphuret, which combines with hydrosulphocyanic acid.

11. Hydrobisulpnocyanic acid is formed in this way. When sulphocyanodide of mercury is gently heated in j sulphuretted hydrogen gas or in muriatic acid gas, it un- : dergoes decomposition, and sulphuret or chloride of mercury is formed, together with a liquid which is deposited in the coldest part of the vessel in drops. They are at first colourless, but soon become yellow, and form small transparent crystals grouped in stars. These crystals undergo spontaneous decomposition, hydrocyanic acid being given out, and an orange-yellow opaque substance remains, which is insoluble in water. Wohler considers this substance as composed of
[table]

12. Disulphide of cyanogen may be obtained in the following manner: Into a small globular glass vessel put some cyanodide of mercury in the state of a fine powder, and pour over it about half its weight of bichloride of sulphur. Shut the vessel, and expose it for a fortnight to the action of light. A number of small crystals are gradually deposited on the upper part of the glass, while at the bottom of the glass there remains corrosive sublimate mixed with a yellow-coloured matter. The crystals may be purified by mixing them with carbonate of lime, and then subliming them.

These crystals, when thus purified, are rhomboidal plates, like chloride of potash. When a minute portion is applied to the tongue it occasions as much pain as if a sharp instrument were thrust into the place. It has a strong smell, similar to that of chloride of cyanogen. It sublimes of its own accord in close vessels at the temperature of the atmosphere. It dissolves readily in water, and is still more soluble in alcohol. It combines with bases, and therefore possesses the characters of an acid. By galvanism it is decomposed, sulphur being deposited at the positive pole and hydrocyanic acid at the negative pole. From the analysis of Lassaigne, it appears to be a compound of
[table]

13. Seleniocyanogen is formed by the same process as was given for forming hydrosulphocyanic acid, only substituting selenium for sulphur. It has not yet been obtained in a separate state, but only in combination with potash, and the salt possesses precisely the properties of sulphocyanodide of potassium.

14. Hydroferrocyanic acid is the acid which exists in the salt usually called prussiate of potaslι or ferroprussiate of potash, a yellow-coloured salt, which crystallizes in truncated octahedrons. It has a saline, cooling, and disagreeable taste, and has been long known from the property which it has of forming Prussian blue when mixed with a solution of iron. To obtain hydroferrocyanic acid from this salt, the following process may be followed: Form ferroprussiate of barytes. Dissolve this salt in cold water, and for every ten grains of it add 2∙53 grains of real sulphuric acid. Agitate the mixture, and set it aside for some time. The sulphate of barytes falls down, and [7:6:436] the water holds in solution hydroferrocyanic acid. It has a pale lemon-yellow colour, and is destitute of smell. It is decomposed by a gentle heat or by exposure to a strong light. From the way in which this acid is obtained, it must be a compound of
[table]

Or we may consider it as a solution of one atom of cyanodide of iron in two atoms of hydrocyanic acid.

15. Azulmic acid is the name given by Boullay to the charry matter formed by the spontaneous decomposition of cyanogen. It is insoluble in water and alcohol; but it dissolves in concentrated nitric acid, to which it communicates an aurora-red colour. The solution is rendered muddy by water. It dissolves with great facility in alkaline leys and in liquid ammonia. The solutions are similar to those of ulmate of potash, but a good deal more red. Acids precipitate a very light brownish-red powder, which, when dry, has no brilliancy, and resembles China-ink in colour. Its constituents, according to Boullay, are,
[table]

When potash is digested with glue, a quantity of azulmic acid is said to be formed, just as ulmic acid is formed when sugar of grapes is digested with the same base. It was for this reason that Boullay gave it the name of azulmic, meaning probably ulmic acid containing azote.

CLASS VII. SULPHUR ACIDS.

The greater number of the acidifiable bases have the property of combining with sulphur and constituting acids; while the alkalifiable bases, when combined with sulphur, are converted into alkaline bodies. In general, when a sulphur acid is placed in contact with an oxygen base, decomposition takes place; for sulphur acids combine only with sulphur bases. It is convenient to be able to distinguish the sulphur acids from the sulphur bases. To attain this object we shall call all the acid sulphur compounds sulphides, while the old term sulphuret will be restricted to the alkaline bodies formed by means of sulphur. Thus sulphide of hydrogen is an acid, while sulphuret of potassium is a base.

The names of the different sulphur acids at present known are as follows :—
[table]

All these sulphur acids have been described in a preced-: ing part of this article, when treating of their respective 1 bases.

CHAP . II. OF ALKALIES.

The alkalies consist of the simple bodies described in a former part of this article under the name of simple alka-liflable bases, united either to oxygen, chlorine, bromine, iodine, fluorine, sulphur, selenium, &c. There are therefore as many classes of alkalies as there are of acids. Besides these different classes of what may be called alkalies with simple bases, there is an alkali composed of two acidifiable bases joined together, namely, ammonia, which is a compound of azote and hydrogen. These two bodies are both electropositive, as is the case with the alkaline bases: we need not therefore be surprised at their constituting an alkali when combined. There are about twenty compound vegetable bodies which possess alkaline properties, composed of carbon, hydrogen, azote, and oxygen, united together. These may be called compound or complex alkaline bodies, in contradistinction to the alkalies with simple bases. We shall reserve the account of these bodies for the last part of this article, in which we shall describe the nature and properties of animal and vegetable bodies. The following are the names of the alkaline bodies with a simple base at present known.

1. Potash.

2. Soda.

3. Lithia.

4. Barytes.

5. Strontian.

6. Lime.

7. Magnesia.

8. Alumina.

9. Glucina.

10. Yttria.

11. Protoxide of cerium.

12. Peroxide of cerium.

13. Zirconia.

14. Thorina.

15. Protoxide of iron.

16. Peroxide of iron.

17. Protoxide of manganese.

18. Sesquioxide of manganese.

19. Protoxide of nickel.

20. Protoxide of cobalt.

21. Oxide of zinc.

22. Oxide of cadmium.

23. Protoxide of lead.

24. Protoxide of tin.

25. Peroxide of tin.

26. Oxide of bismuth.

27. Suboxide of copper.

28. Oxide of copper.

29. Suboxide of mercury.

30. Oxide of mercury.

31. Oxide of silver.

32. Oxide of arsenic?

33. Protoxide of antimony.

34. Oxide of tellurium.

35. Oxide of chromium.

36. Protoxide of uranium.

37. Peroxide of uranium.

38. Protoxide ofmolybdenum.

39. Deutoxide of molybdenum.

40. Protoxide of tungsten.

41. Deutoxide of tungsten.

42. Oxide of titanium.

43. Oxide of columbium.

The chlorine, bromine, &c. alkalies are the same as the preceding, substituting the terms chlorides, bromides, &c. respectively, instead of oxides.

Ammonia may also be considered asan alkali with a simple base, if we consider azote as that base, and hydrogen as the electro-positive body with which it is in combination. It might, if a new name were wanted, be denominated terhydrate of azote. CHAP . III. OF NEUTRAL COMPOUNDS.

Under this head a considerable proportion of vegetable and animal bodies might be comprehended. But in consequence of the still imperfect state of vegetable and animal chemistry, it will be better to reserve them to a subsequent part of this article. Here we shall confine ourselves to those neutral bodies that are employed as chemical re-agents, and which, therefore, it is of importance for the student to be acquainted with before he turns his attention to animal and vegetable chemistry. These neutral[7:6:437] substances naturally arrange themselves under the seven following heads;

1. Water.

2. Spirits.

3. Ethers.

4. Ethal.

5. Volatile oils

6. Fixed oils.

7. Bitumens.

Sect. I.— Of Water.

The properties and composition of water have been already explained in a preceding part of this article. A few observations on it as a chemical body still remain to be made.

It has the property of dissolving and combining with almost all the acids, and with several of the alkaline bodies; and as it shows an equal disposition to combine with either, and does not destroy nor conceal their acid and alkaline qualities, it is obvious that it is a neutral body. It dissolves also a considerable number of the salts, which are compounds of an acid and base. The quantity of each of these bodies which water can dissolve has a limit, and it is very various with respect to different salts. When water has dissolved as much of a salt as it can take up, we say that it is saturated with salt.

The power which thus limits the solvent property of water is the attraction which exists between the particles of the salt. When a salt is dissolved in water its particles must be equally dispersed through every part of the liquid. They must of course be arranged in regular rank and file; and the greater the quantity dissolved the smaller must the distance be between every two particles of the salt. It would appear that the greater the number of particles of salt which are dissolved by the water, the smaller is the force by which the salt and water are united.

, Water not only dissolves many salts and other bodies, but it has the property of entering into combination with a great many bodies in a solid state, constituting compounds, to which the name of hydrates has been given. There are few or none of the simple bodies that form hydrates. The supporters of combustion are soluble in it to a trifling extent; and the same remark applies to hydrogen and azote; but none of the other bases, whether acid or alkaline, are capable of uniting with it. Most of the acids are capable of forming hydrates. Such hydrates are usually called crystals of the acid. Sometimes they are in the state of powders, and sometimes they constitute jellies. Most of the alkaline bases, in like manner, constitute hydrates, some of them in crystals, but a much greater number in the state of dry powders.

Sect. II.— Of Ardent Spirits.

The term ardent spirits in this country is usually applied to the liquid obtained by distillation from different fermented liquors. But of late years two distinct species of liquid have been discovered, bearing a close resemblance to the spirits from fermented liquors usually called alcohol. These are obtained not by fermentation, but by heat. They have been called pyroacetic and pyrolig-nic spirits. We shall treat of all the three in this section.

1. Alcohol.

Fermented liquors are either the expressed juices of fruits or the hot infusions of malt. The former are called wines, the latter beer or ale. The distillation of either of these liquors furnishes alcohol, and the alcohol is always the same, whatever the liquor be from which it was obtained. When these spirits, distinguished by .the names of brandy, rum, whisky, gin, arrack, &c. according to the liquid which yields them, are redistilled, the first portion that comes over is a fine, light, transparent liquid, known in ' commerce by the name of rectified spirits, and usually sold under the name of spirit of wine. "When dry carbonate of potash or chloride of calcium is mixed with this liquor in a retort, in the requisite proportion, and heat applied, there comes over a quantity of spirit as strong as it is possible to make it. When in this state it is called alcohol.

Alcohol thus procured is a transparent liquid, colourless as water, having a well-known smell, rather strong, but not unpleasant. Its taste is hot and biting, but generally considered as agreeable; and when taken internally in considerable quantities it produces intoxication. Its specific gravity at 60° is 0∙79460. WTιen mixed with water a liquid is obtained, whose specific gravity increases with the quantity of water; but as the two liquids undergo mutual condensation, the specific gravity is always higher than the mean. The condensation is greatest when one atom of alcohol combines with three atoms of water. The specific gravity of such a combination, supposing no condensation to take place, would be 0∙89373; but its actual specific gravity is 0∙92662, so that the increase amounts to 0Ό3289. The following table exhibits the specific gravities of different atomic mixtures of alcohol and water, the specific gravity supposing no increase of density, and the amount of the condensation. It was drawn up by Dr Steel from his own experiments, which were made with great care.
[table]

Alcohol boils when heated to 173^- o . It has never yet been frozen, though it has been exposed to a temperature as low as — 90°. The boiling point, however, varies with the'strength of the liquid. If the alcohol be of the specific gravity 0∙818, it boils at 174° ∙2; when of the specific gravity 0∙903, it boils at 179° ∙96; and when of the specific gravity 0*980, it boils at 195° ∙8. The specific gravity of the vapour of alcohol is L6000, if we reckon the specific gravity of air unity.

Alcohol burns readily with a blue flame, and gives but little light, though it produces a great deal of heat. By combustion it is totally converted into water and carbonic acid gas. When alcohol is passed through a red-hot porcelain tube, it is in a great measure resolved into water and olefiant gas. By determining the quantity of water and olefiant gas formed, when a given weight of alcohol was decomposed in this way, Saussure concluded that alcohol in the state of vapour is a compound of one volume olefiant gas and one volume steam united together and condensed into one volume.
[table]

This would make the specific gravity of alcohol vapour 1∙5972, which is very near the truth.

. As olefiant gas is a compound of two atoms carbon and [7:6:438] two atoms hydrogen, and water of one atom hydrogen and one atom oxygen, it is obvious that alcohol is a compound of
[table]

so that its atomic weight is 2∙875. The analysis of Saussure has been confirmed by the subsequent analyses of Dumas and Boullay, who obtained 3∙07 atoms hydrogen, 2Ό17 atoms carbon, and 1 atom oxygen, constituting a very near approximation to the truth.

Alcohol dissolves bromine and iodine, and forms very deep-coloured solutions. Chlorine is absorbed by it in considerable quantity, but the alcohol undergoes an alteration. Phosphorus and sulphur are dissolved by it in small proportions. Alcohol dissolves a considerable number of acids, several but not many of the alkaline bodies, and a considerable number of salts. But these points will bebest noticed when treating of the substances themselves which dissolve in this liquid.

Mr Graham has shown that several salts, when dissolved in alcohol, are capable of crystallizing, and of retaining a quantity of alcohol essential to the crystalline form of the salt. Such crystals he calls alcoates.

2. Pyro-acetic Spirit.

This liquid was discovered in 1807 by Derosne, during the distillation of verdigris. When the acetates of lead, zinc, or manganese, or still better of potash or soda, are distilled in a retort with as low a heat as possible, there comes over acetic acid and pyro-acetic spirit. By saturating the liquid in the receiver with an alkali, and distilling again, the pyro-acetic acid is obtained in a separate state. It is a colourless, limpid liquid, having an acrid and hot taste, but leaving a cooling impression in the mouth. Its smell is peculiar, and has been compared to that of a mixture of oil of peppermint and bitter almonds. Its specific gravity is 0∙7864. It burns with a flame, white exteriorly, and of a fine blue within, and it leaves no residue. It boils at the temperature of 165°. It mixes with water, alcohol, and volatile oils, in any proportion. According to the analysis of Macaire and Marcet, it is composed of
[table]

Thus it contains two atoms of carbon and one atom of oxygen more than alcohol.

3. Pyroxylic Spirit.

This liquid is obtained when wood is distilled. The products of the distillation are water, acetic acid, pyroxylic spirit, empyreumatic oil, and a black matter like tar. When the watery portion, freed as well as possible from the other ingredients, is distilled at a low heat, the first portion that comes over is pyroxylic spirit. It may be freed from acetic acid by agitation with lime or magnesia, and distillation at a low temperature. It is still contaminated with oil, from which, however, it may be nearly freed by mixing it with its own weight of sulphuric acid, and distilling again.

It is transparent and colourless, having a pungent and somewhat ethereal smell. Its taste is hot, pungent, and very disagreeable from the empyreumatic oil which it holds in solution. Its specific gravity is 0∙8121. It boils at 150°. It burns with a very pale yellow flame inclining to blue, and leaves no residue. It dissolves in alcohol in any proportion. With water it becomes milky, obviously from the empyreumatic oil which it contains. It dissolves readily in oil of turpentine and in liquid potash. Camphor dissolves in it readily, but it does not dissolve olive oil. With sulphuric ether it unites in all proportions. According to the analysis of Marcet and Macaire, its constituents are,
[table]

But as the spirit is always contaminated with empyreumati( oil, no conclusion can be drawn from this result. A por∙ tion of the hydrogen and carbon is undoubtedly owing to the presence of that oil.

Sect. III.— Of Sulphuric Ether.

The term ether is applied indiscriminately to all the volatile liquids formed by the action of acids on alcohol. But these liquids are divisible into two sets, exceedingly different from each other in their characters. One set is quite free from any portion of the acid employed in its preparation, and consists of the very same constituents as alcohol, though the proportions are different; the other set consists of the acid employed in the formation of the ether, saturated with a peculiar volatile and combustible substance, which appears to be the same in all. The first of these shall occupy our attention in this section, and the second set in the following section.

Sulphuric ether is made in the following manner: A mixture of equal parts of alcohol and sulphuric acid is put into a retort, to which a large receiver is luted; and the receiver .should be surrounded with ice, or at least with cold water. Heat is applied, and as soon as the mixture boils, the ether comes over, and runs in large striae down the sides of the receiver. As soon as the ether amounts to one half of the alcohol used, the process must be stopped. To free it from alcohol and sulphurous acid, with which it is always contaminated, it is agitated in a close phial with a little water and slaked lime, till the smell of sulphurous acid is destroyed; then decant off the ether into a retort, and distil it over.

Ether is a limpid, colourless liquid, having a fragrant smell, and a hot, pungent taste. It is so volatile that it can scarcely be poured from one vessel to another without losing a considerable portion by evaporation. Wlιen poured out in the open air it disappears in an instant During its evaporation a considerable degree of cold is produced. It boils in metal vessels at the temperature of 96°. The specific gravity of the vapour is 2∙5694∙ It does not freeze, according to Thenard, though cooled down to — 58°. When admitted to a gas it increases its volume very considerably', and even doubles it if the temperature be not too low. When one volume of the vapour of ether is mixed with six volumes of oxygen gas, and an electric spark passed through the mixture, a violent detonation takes place, and the whole ether is converted into carbonic acid gas and water. The residue, after the combustion, consists of four volumes of carbonic acid gas. From this experiment it follows, that a volume of ether is a compound of four volumes carbon vapour and four volumes hydrogen gas, condensed into one volume, and combined with a volume of the vapour of water; so that its constituents are,
[table]

Thus ether is a compound analogous to alcohol. Alcohol [7:6:439] is a compound of a volume of olefiant gas and a volume of vapour of water united together and condensed into a liquid; while ether is a compound of one volume of tetarto-cαrbo∙hydrogen and one volume of vapour of water united together and condensed into a liquid.

By tetarto-carbo-hydrogen is meant a compound of such a nature, that when in the gaseous state one volume of it is composed of
[table]

so that its specific gravity is 1∙9444, or just double that of olefiant gas.

Water dissolves about one tenth of its weight of ether. Hence common ether, when agitated with water, is freed of its alcohol; but a portion of the ether is lost, which augments according to the proportion of water employed. In alcohol it dissolves in any proportion whatever. Ether dissolves phosphorus, sulphur, iodine, potash, and many other bodies, especially the acids, a considerable number of which are taken up by it.

Much light has been thrown upon the theory of etherification by the late experiments of Mr Hennell. When equal weights of alcohol and sulphuric acid are mixed together without the application of any heat, about one half of the sulphuric acid is converted into theiovinic, which is a compound of two atoms sulphuric acid and one atom tetarto-carbo-hydrogen. When this mixture is distilled, ether is formed, and passes over into the receiver, while the theiovinic acid disappears. The ether seems to originate from the tetarto-carbo-hydrogen in the theiovinic acid. That substance is induced by the action of heat to quit the sulphuric acid with which it was previously combined, and to unite with an atom of water. The sulphuric acid thus set at liberty acts upon a new portion of the alcohol, and converts it into theiovinic acid, which the heat afterwards decomposes.

In preparing ether, if we change the receiver after the ether ceases to come over, and continue the heat, sulphurous acid comes over in abundance, and a yellowish liquor quite different from ether. If we purify this liquid by means of a weak solution of carbonate of potash, it constitutes what is called sweet oil of wine. It has a yellow colour, a fragrant smell, a bitterish and pungent taste, and a specific gravity of 1 ’ 060. It does not mix with ether, but combines with alcohol. Mr Hennell has shown that it is a compound of two atoms sulphuric acid and two atoms tetarto-carbo-hydrogen. When it is kept, one half of the tetarto-carbo-hydrogen separates in a crystalline form, and the sweet oil of wine becomes theiovinic acid. If we agitate this oil of wine with a sufficient quantity of water, it is converted into theiovinic acid, and the excess of tetarto-carbo-hydrogen is separated in the form of a bright ambercoloured oil of the consistency of castor oil. Its specific gravity is 0 ’ 9. It is insoluble in water, very soluble in ether, and somewhat less so in alcohol. It burns with a brilliant flame, throwing off* some carbon.

Sect. IV.— Of Acid Ethers.

These ethers are distinguished by the epithet acid, not because they have acid properties, which is not the case, but because they contain an acid as one of their constituents. They are twelve in number, and naturally divide themselves into two sets; namely, those that contain a hydra-cid or chlorine as a constituent, and those which contain an oxygen acid. The first set comprehends four ethers; namely, muriatic ether, chloric ether, hydrobromic ether, and lujdriodic ether. The second set contains eight ethers; namely, nitric, oxalic, acetic, benzoic, formic, tartaric, ci tric, and malic ethers. All these ethers are made by distilling mixtures of alcohol and the acid which enters into each as a constituent. Scarcely any of them has been applied to any use, if we except nitric ether and acetic ether; the former of which is frequently employed in medicine, and the letter occasionally, though much more rarely.

1. Muriatic ether. — Put equal bulks of alcohol and mu-ĵ riatic acid, both as strong as possible, into a retort of sucht a size as not to hold much more than the mixture. A few grains of sand, or of platinum wire, should be put into the retort, to prevent violent agitation in boiling. Let a tube luted to the beak of the retort enter a Woulfe’s bottle double the size of the retort, half filled with water, and furnished with a tube of safety. From this bottle a tube passes to collect the muriatic ether in the state of gas in proper vessels. When heat is applied the muriatic ether passes over as a gas.

This gas is colourless: it has a strong ethereal smell, and a sweetish taste. Its specific gravity is 2 ’ 219, that of air being one. At 64° water dissolves its own bulk of this gas. When cooled down to 52° it is condensed into a liquid. In its liquid form it is colourless and transparent. At 41° its specific gravity is 0∙874. It is much more volatile than sulphuric ether, assuming the gaseous form when heated a little above 52°. It would appear from the analysis of Thenard that it is a compound of one volume of tetarto∙carbo-hydrogen and one volume muriatic acid gas condensed into one and a third volume. Supposing this composition correct, the constituents are,
[table]

2. Chloric ether is obtained by passing a current of chlorine gas through alcohol or sulphuric ether till these liquids refuse to absorb any more. When the process is terminated, an oily matter is precipitated to the bottom, the quantity of which is increased when the liquid swimming over this oil is saturated with potash. This oily-looking substance is chloric ether.

It is a thin oily-looking fluid, having a specific gravity of 1∙134. It is more volatile than water, has a smell somewhat similar to that of nitric ether, and an aromatic, hot, and somewhat bitter taste. It is very little soluble in water. It has not yet been analysed.

3. Hydroibromic ether was formed in this manner. Forty parts of alcohol of the specific gravity of 0∙827 were put into a small tubulated retort. To this one part of phosphorus was added, and finally eight parts of bromine were poured in by little at a time. Every time that bromine came in contact with the phosphorus, a rapid combination took place, and hydrobromic and phosphorous acids were formed. The mixture was now distilled by a gentle heat, and the product mixed with water. The ether separated and sunk to the bottom. It is colourless and transparent, heavier than water, has a strong ethereal smell, a sharp taste, and is very volatile. It is soluble in alcohol.

4. Hydriodic ether may be formed by a similar process.

5. What is called sulphocyanic ether may be formed by mixing one part of sulphocyanodide of potassium, two parts of sulphuric acid, and three parts of alcohol of the specific gravity 0*848, and distilling. The product of the distillation being mixed with water, the ether separates in an oleaginous state. This ether might probably be useful as a medicine.

6. Nitric ether. — This ether, which, next to the sulphuric,; is the most important of all, may be prepared in the fol-< lowing way: Put into a retort equal weights of alcohol [7:6:440] and nitric acid of the specific gravity 1∙283. Lute a bent tube to the beak of the retort, and plunge it to the bottom of a Woulfe’s bottle half filled with a saturated solution of salt in water. From this bottle a tube passes to the bottom of a second Woulfe’s bottle half filled with the same liquid. Join in this way five Woulfe’s bottles, and surround each with a mixture of snow and salt, to keep it as cool as possible. Heat being applied to the retort, a violent effervescence takes place, which must be moderated by withdrawing the fire and moistening the belly of the retort with cold water applied by a sponge or a wet cloth. Gaseous matter passes off with rapidity, carrying with it the ether which is deposited on the surface of the liquids in the Woulfe’s bottles, chiefly in the first bottle. To free it from uncombined acid, put it into a well-stopped phial, and agitate it with a quantity of chalk till it ceases to affect vegetable blues.

It has a slight-yellowish colour, and a strong ethereal smell. Its taste is strong, and quite peculiar. It is heavier than alcohol, and much more volatile than sulphuric ether. The specific gravity of its vapour is 2∙627. When liquid, it is lighter than water, and requires forty-eight parts of that liquid to dissolve it; and it communicates to it an odour similar to that of apples. In alcohol it dissolves in every proportion. It burns brilliantly with a white flame, like sulphuric acid. When kept for some time, both nitric and acetic acids are evolved in it, though neither of them can be detected at first. It was carefully analysed by Dumas and Boullay, who found its constituents
[table]

Now these atomic proportions are equivalent to
[table]

But sulphuric ether is a compound of one atom tetarto-carbo-hydrogen and one atom water. We may therefore consider nitric ether as a compound of one atom sulphuric ether and one atom hyponitrous acid; and in the gaseous state it is a compound of one volume sulphuric ether and one volume hyponitrous vapour united together without any alteration of volume
[table]

gravity of nitric ether vapour. Now the specific gravity, as determined by Boullay, is 2’627, which is within one per cent, of the calculated gravity.

7. Oxalic ether. — To prepare this ether, mix together in a retort one part of alcohol, one part of binoxalate of potash, and two parts of sulphuric acid, and distil. There comes over, first alcohol, then sulphuric ether, and at last an oleaginous liquid which collects at the bottom of the receiver. The distillation may be continued till, all the alcohol is driven out of the retort, the last portions being richest in oxalic ether. Pour the oleaginous liquor into a tall jar containing water. At first it floats, but in proportion as the sulphuric ether which it contains evaporates, it falls in large drops to the bottom of the jar. It is now to be poured on powdered litharge, and boiled till the boiling point rises to 263°. This deprives it of sulphuric acid, alcohol, and water, with which it was contaminated. Let it be now poured into a dry retort and distilled over.

It is an oleaginous liquid, having a specific gravity of 1∙0929. It boils at 263°. Its smell is aromatic, but has something analogous to that of garlic or phosphorus. The specific gravity of its vapour is 5Ό87, that of air being reckoned 1. This ether, according to the analysis of Dumas and Boullay, is composed of
[table]

Now an atom of oxalic acid is composed of
[table]

If we subtract 4’5 from 9∙125, the remainder will be 4*625, which is just the weight of an integrant particle of sulphuric ether, and consists also of the same atomic constituent; for sulphuric ether is a compound of
[table]

Thus we see that oxalic ether is a compound of
[table]

When ammoniacal gas is passed through this ether, one half of the tetarto-carbo-hydrogen combines with the oxalic acid, and forms an acid which may be called oxalovinic acid; and this acid combines with the ammonia, forming a binoxalovinate of ammonia.

8. Acetic ether. — When equal weights of concentrated, acetic acid and alcohol are mixed in a retort and distilled* a great many times, pouring back the liquid each time from the receiver to the retort, an acetic ether is obtained, mixed with alcohol, from which it is not an easy matter to separate it by repeated washings with water.

Acetic ether is limpid and colourless. It has an agreeable odour of ether and acetic acid. It has a peculiar taste. Its specific gravity is 0’882. It boils at I65°. The specific gravity of its vapour is 3Ό67. It burns with a yellowish-white flame, and acetic acid is developed during its combustion. It does not undergo any change by keeping. At the temperature of 62° it requires more than seven times its weight of water to dissolve it. It was analysed by Dumas and Boullay, and found composed of
[table]

Acetic acid is a compound of two atoms hydrogen, four atoms carbon, and three atoms oxygen, and its atomic weight is 6 ’ 25. If we subtract this from 10 ’ 875 (the weight of an atom of acetic ether), there will remain 4∙625, which is the weight of an atom of sulphuric ether. The atomic constitution is also the same. It is obvious, therefore, that acetic ether, like oxalic and nitric, is a compound of
[table]
[7:6:441]

9. Benzoic ether is prepared by distilling a mixture of four parts of alcohol, two parts of benzoic acid, and one part of muriatic acid, till half the liquid passes over. It is then poured back, and the process repeated two or three times. The greater part of the ether exists in the liquid remaining in the retort. It is separated by means of water. If we boil it on powdered litharge till the boiling point becomes fixed, and afterwards distil it over with caution, we obtain it in a state of purity.

It is a colourless, oily-looking fluid. It has a weak smell, a pungent taste, and a specific gravity of 1∙0539. Its boiling point is 409°. The specific gravity of its vapour is 5∙409. It has been analysed by Dumas and Boullay, and shown to be composed of
[table]

The remaining ethers, the formic, tartaric, citric, and malic, have been but superficially examined, and none of them has been analysed. From analogy, however, we can have little doubt that each is composed of an atom of sulphuric ether united to an atom of the respective acids employed in the formation of the ethers.

Sect. V.— Of Ethal.

This substance was obtained by Chevreul from spermaceti, and named, from its supposed analogy to alcohol and sulphuric ether, from the two first syllables of these two names.

Spermaceti was purified by repeated solutions in alcohol, which frees it from a yellow oil which it contains. So purified, it has been called cetine. The cetine is converted into a soap by mixing a hundred parts of it with a hundred parts of potash dissolved in two hundred parts of water, and keeping the solution in a temperature between 122° and 194°, agitating it frequently. When the saponification is complete, an excess of tartaric or phosphoric acid is added, and the heat kept up till the whole fatty matter collects on the surface. This fatty matter is a mixture of ethal and margaric and oleic acids. When heated with barytes water, the acids are removed, and the excess of barytes is afterwards removed by boiling the ethal in distilled water. Absolute alcohol now dissolves the pure ethal from the purified fatty matter. Heat drives off the alcohol, and leaves the ethal pure.

. Ethal is a solid, colourless body, having the translucency of wax. It melts at about 118°. When cooled slowly it crystallizes in brilliant plates. It has no smell, and scarcely any taste. It may be volatilized. Alcohol of 0∙812 dissolves it in any proportion at the temperature of 129°; but it is deposited partly in crystals as the solution cools. It is insoluble in water. It does not combine with potash nor form soap when pure, but it forms a soap when mixed with a small quantity of margaric or oleic acids. It burns like wax. According to the analysis of Chevreul, which, however, cannot be admitted to be more than an approximation, ethal is a compound of
[table]

According to this analysis, 10, or a multiple of that number, must represent the atomic weight of ethal.

Sect. VI.— Of Volatile Oils.

The term oil is applied to a number of unctuous fluids, which, when dropt upon paper, sink into it, and make it semitransparent, or give it what is called a greasy stain. These bodies are very numerous, and have been divided into volatile ĩcrA fixed oils. Volatile, called also essential oils, possess the following properties:

1. Liquid; often as liquid as water; sometimes viscid or solid.

2. Very combustible.

3. An acrid taste, and a strong fragrant odour.

4. Volatilized with water at a temperature not higher than 212°

5. Soluble in alcohol and ether, and slightly so in water.

6. Evaporate without leaving any stain upon paper. By this last test we can easily discover whether they have been fraudulently mixed with fixed oils. Let a drop of the suspected oil fall on a leaf of writing paper, and then apply a gentle heat. If the oil evaporate without leaving a stain, it is pure; if it leaves a stain it has been mixed with a fixed oil.

Volatile oils exist in great abundance in plants. All the fragrance of the vegetable kingdom is owing to them. They are usually obtained by putting the part of the vegetable containing them into a still with water, and distilling the liquid over. The oil passes over with the water, on which it usually swims.

The specific gravity of volatile oils is commonly less than that of water. Oils of sassafras, of cinnamon, and of cloves, are heavier than water. Oil of turpentine, the lightest of the volatile oils, has a specific gravity of 0∙792.

Volatile oils do not combine with alkalies and form soaps. By the action of light many of them are converted into resinous bodies, which combine readily enough with alkalies.

Sulphuric acid acts upon them with considerable energy, converting them first into a resinous substance, and at last to the state of charcoal. Muriatic acid has but little action on them. When nitric acid is thrown upon them suddenly, it sets them on fire.

A variety of these oils have been analysed by burning them in oxygen gas, and ascertaining the quantity of oxygen consumed, and the volume of carbonic acid formed. What prevents the results of these experiments from being depended on, is the difficulty of obtaining volatile oil free from all admixture of foreign bodies. They are almost all mixtures of various volatile oils, differing in their volatility, &c., which it has been impossible hitherto to separate so as to obtain each in an insulated state. They consist chiefly of hydrogen and carbon, sometimes with a little oxygen, and sometimes without any. The atoms of carbon are always more numerous than those of hydrogen; sometimes twice as numerous, as in solid anise oil; sometimes as three to two, as in liquid anise oil and oil of rosemary; sometimes approaching equality, as in oil of roses.

Sect. VII.— Of Fixed Oils. Fixed oils are distinguished by the following characters:

1. Liquid; or, if solid, easily melt when exposed to a< gentle heat. 1

2. An unctuous feel.

3. Very ’ combustible.

4. A mild taste.

5. Little smell.

6. Boiling point not under 600°.

7. Insoluble in water, and nearly so in alcohol.

8. Leave a greasy stain on paper.

These oils, called also expressed oils, from the mode of procuring them, are numerous, and arc obtained partly from vegetables, partly from animals, by simple expression. They exist usually in the seeds of cruciform plants.
[7:6:442]

They are all lighter than water; palm-oil, the heaviest, having a specific gravity of 0∙968, while neat’s-foot oil has a specific gravity of 0∙8795.

They do not begin to evaporate till they have been heated above the boiling point of water. As the heat increases, a pretty abundant vapour may be seen to rise from them; but they do not begin to boil till heated up to about 600°. At that temperature, or a little above it, they may be distilled over; but they are always somewhat altered by the process. The distilled oil is darker coloured, much more liquid, and much more volatile, than before.

When they are exposed to the open air they have the property of absorbing oxygen gas, and gradually become solid. Now there are some oils which remain transparent, when thus solidified, and which no longer possess the characters of oil, but are become quite hard, and incapable of staining other bodies. There arc others which assume the appearance of tallow, easily melt when heated, and, when thus melted, possess all the characters of oily bodies, the same as before they underwent the change of state. This has occasioned the division of the fixed oils into drying oils and fat oils.

1. Drying Oils.

The principal dry oils are the following:

1. Linseed oil, from the seeds of linum usitatissimum.

2. Walnut oil, from the fruit of juglans regia.

3. Hemp oil, from the seeds of cannabis sativa.

4. Poppy oil, from the seeds of papaver somniferum.

5. Castor oil, from the seeds of ricinus communis.

6. Croton oil, from the seeds of eroton tiglium.

7. Grapeseed oil, from the seeds of vitis vinifera.

8. Nightshade oil, from the seeds of atropa belladonna.

9. Tobacco oil, from the seeds of nieotiana tabacum.

10. Henbane oil, from the seeds of hyoscyamus niger.

11. Sunflower oil, from the seeds of helianthus annuus.

12. Cress oil, from the seeds of lepidium sativum.

These oils, in their natural state, possess the property of drying oils but imperfectly. To prepare them for the use of the painter and varnish-maker, they are boiled for some time in an iron pot. By this process they arc partly decomposed, abundance of watery vapour and of carburetted hydrogen gas being separated from them. They become deeper coloured, and acquire greater consistency'. It is common for some purposes to set them on fire, to allow them to burn for some time, to extinguish them by covering up the vessel in which they are contained, and to continue the boiling till they acquire the proper degree of viscidity. By this process they lose much of their unctuous quality, so as not to leave a greasy stain upon paper.

2. Eat Oils.

The principal fat oils are the following:

1. Olive oil, from the fruit of olea Europea.

2. Almond oil,' from the kernel of amygdalus communis.

3. Rape oil, from brassica rapa.

4. Mustard oil, from sinapis alba and nigra.

5. Plum oil, from prunus domestica.

6. Beech oil, from fagus sylvatica.

7. Hazel oil, from corylus avellana.

8. Oil of ants.

9. Oil of eggs.

10. Trane or whale oil.

11. Spermaceti oil.

These oils, when exposed to the air and light, absorb oxygen, and are converted into a substance like tallow. They are used, at least olive oil, for making soap, and also for making plasters.

3. Solid Oils.

The principal solid oils are:

1. Cacao butter, from the theobroma cacao.

2. Palm oil, from eocoa butyracca.

3. Museat balsam, from myristica officinalis.

4. Laurel oil, from laurus nobilis.

5. Japan wax.

6. Myrtle wax, from myrica cerisera.

7. Bees wax.

8. Coco oil, from cocos nucifera.

9. Butter of galam.

10. IIcg’s lard.

11. Common butter.

12. Tallow.

The melting point of these solid oils is very different. Palm oil melts at.84°, Japan wax at 98°.

We are indebted to Chevreul for a great deal of important information respecting the fixed oils. They are all compounds of two or three different substances, which may be separated from each other. These substances arc stearine, elaine, cetine, phoccnine, butyrine, hircine, and Cholesterine.

1. Stearine. — Tallow and animal fat are mixtures of stearine and elaine, the first of which is solid, and the second liquid. Stearine may be obtained by heating hog’s lard in boiling alcohol. When the liquid cools it deposits white crystalline needles, which are stearine, or we may obtain it from olive oil by freezing the oil, and while in that state subjecting it to pressure between numerous folds of blotting paper. The paper takes up the elaine and leaves the stearine. It is white, brittle, and has somewhat of the appearance of wax. It has little or no taste or smell. When heated to about 109° it melts into a liquid oil. It is somewhat soluble in alcohol, but the solubility varies in the stearine from different substances. When digested with alkaline bodies it is converted into soap, leaving a small portion in the state of the sweet principle of oils. According to Chevreul, it is a compound of
[table]

2. Elaine. — When tallow is dissolved in hot alcohol, the stearine is deposited when the alcohol cools. By distilling the residual liquid, the alcohol is driven over, and the elaine remains behind. When stearine is obtained by subjecting frozen oils to pressure between folds of blotting paper, the elaine is absorbed by the paper; and if this paper be soaked in water, and subjected to pressure, the elaine is forced out, and may be obtained in a separate state.

Elaine has much the appearance of a vegetable fixed oil, and is quite liquid at the’temperature of 59°. When pure, it is colourless, and destitute of smell. It is lighter than water, and is very soluble in alcohol, but insoluble in water. When digested with potash ley it is converted into a soap, leaving rather a greater proportion of the sweet principle of oils than stearine does. Elaine, front Chevreul’s analysis, is a compound of
[table]

But no great degree of confidence can be put in this analysis.

3. Cetine. — Spermaceti is a combination of cetine and a yellow oil, from which it is separated by repeated solutions in alcohol and crystallizations. It forms white brilliant plates. At 680° it may be volatilized without decomposition[7:6:443]. It has a very slight smell, but is destitute of taste. It is insoluble in water. One hundred parts of alcohol of the specific gravity 0∙821 dissolve 2 - 5 parts of cetine, the greater part of which is deposited as the solution cools. Potash converts it into ethal and margaric acid. When heated sufficiently it takes fire and burns like wax. Sulphuric acid gradually decomposes it by the assistance of heat. The constituents, according to Chev-reul’s analysis, are,
[table]

4. Phocenine. — It may be obtained from the oil of the common porpoise, by dissolving the oil in alcohol, and setting it aside for twenty-four hours. The alcohol swims on the top. This alcoliolic liquid being distilled, leaves an acid oil of the specific gravity 0 ’ 931. Being deprived of its acid, and treated with weak cold alcohol, phocenine is obtained.

It is a very fluid oil, of the specific gravity 0∙954. Its odour is slight, but peculiar. It is very soluble in alcohol. When treated with potash it is converted into phocenic and oleic acids, while a quantity of sweet principle of oil remains.

5. Butyrine. — Butter, besides stearine, contains two distinct oily bodies, one of which is butyrine. To procure it, free the butter of all traces of butter-milk. When kept for some days at the temperature of 66°, it separates into a granular substance, consisting of stearine, not quite free from the oily bodies, and a liquid, consisting of the two oils, still retaining stearine in solution. This liquid is yellow, and has a taste like butter. Its specific gravity is 0∙922. Digest it repeatedly in absolute alcohol till the whole is dissolved. Set the solution aside; a portion of oil gradually separates. Distil the alcoholic solution by a moderate heat. What remains is butyrine.

Butyrine is very fluid at 66°, and has a specific gravity of0∙908. It does not congeal at 32°. It has the flavour of butter. It is insoluble in water, but boiling alcohol of 0 ’ 822 dissolves it in any proportion. A solution of twenty butyrine in a hundred alcohol becomes opaque on cooling. It is readily converted into a soap when digested in potash ley.

6. Hircine. — Hircine is a liquid oil which exists in the tallow of the deer and sheep. With elaine it constitutes the liquid portion of the tallow. When saponified it is converted into hircic acid.

7. Cholesterine. — This name has been given to a fatty matter which constitutes the principal constituent of biliary calculi. It may be obtained pure by washing human biliary calculi with water, and then dissolving them in boiling alcohol. As the solution cools, the cholesterine is deposited in crystalline plates.

It is solid, white, and possessed of considerable lustre. It melts at 278°, and, when cooled, slowly crystallizes in radiated plates. It has no taste and little smell. At 680° it may be volatilized. It is insoluble in water. A hundred parts of alcohol of 0∙816 dissolve eighteen parts of cholesterine. Weaker alcohol dissolves less. It gives out no water when heated with protoxide of lead. It cannot be converted into soap, nor does it undergo any alteration when digested with potash ley. Its constituents, as determined by Chevreul, are,
[table]

The fixed oils, like the volatile, are compounds of carbon, hydrogen, and oxygen. A few of them yield small portions of azote, probably derived from some foreign substance contained in them. We must except the oil of ants, which, according to the analysis of Göbel, contains 19∙5 per cent, of azote. The proportion of oxygen seems to be greater than in the volatile oils. Thus Saussure found linseed oil a compound of
[table]

so that 7*875, or some multiple of it, is the atomic weight of this oil. It is unnecessary to give the atomic constitution of the other fixed oils which have been analysed, because there is no doubt that they constitute always mixtures of various oily bodies, which we have it not in our power to separate, and because the mere ratios of the atomic constituents throw no light upon the way in which these bodies are constituted. Linseed oil might be a compound of one atom carbonic oxide and one atom hepta-carbo-hydrogen, but we have no evidence that it is so. Stearine from olive oil, according to the experiments of Saussure, is composed of about
[table]

Thus it contains much less oxygen than linseed oil.

When the fixed oils are saponified, they are converted into the various fatty oils described in the first chapter of this division of our article.

They are insoluble in water. They dissolve, though sparingly, in alcohol, and they arc somewhat more soluble in sulphuric ether. They unite readily with one another, with volatile oils, and with bitumens and resins. They constitute soap when they combine with alkalies. With potash they form soft soap, with soda hard soap, and with other bases soaps which do not dissolve in water, and cannot therefore be employed as detergents.

Sect. VIII.— Of Bitumens.

The term bitumen has often been applied to all the inflammable substances found in the earth; but the meaning of the word is notv so far limited, that mellite sulphur are excluded. It would be proper to exclude amber likewise, and to apply the term bitumen to those bodies which have a certain analogy with fixed oils. They may be divided into two classes, namely, bituminous oils, and solid bitumens.

1. Bituminous Oils.

Only two species of bituminous oils are known. These are petroleum and mineral tallow.

1. Petroleum is an oil of a brownish-yellow colour. When pure it is as fluid as oil of turpentine, and very volatile. Its specific gravity varies from 0∙730 to 0 ’ 878. It has a peculiar smell. It may be distilled over without alteration. When pure it is called naphtha. The oil obtained by distilling pit coal, when properly rectified, seems to be identical with natural naphtha. It burns very brilliantly, giving out at the same time much smoke; It is insoluble in water, though it communicates its smcíl to that liquid. Alcohol dissolves about one fifth of its weight of it. Sulphuric ether, petroleum, fat oils, pitch, and volatile oils combine with naphtha in any proportion. It dissolves wax when assisted by heat, and caoutchouc when [7:6:444] they are boiled together; at least the whole is converted into a transparent varnish.

2. Sea wax or mineral tallow is a solid substance, found first on the banks of the Baikal Lake, in Siberia. It is white, melts when heated, and on cooling assumes the consistence of a white cerate, almost as hard as wax. It dissolves readily in alcohol, and in other respects resembles the characters of the volatile oils. It burns with a bluish-white flame, and gives out much smoke. This substance has been found repeatedly in the Highlands of Scotland. What is called hatchettine, found in Wales, is merely a variety of mineral tallow.

2. Proper Bitumens.

The true bituminous substances may be distinguished by the following properties:

1. They are either solid or of the consistence of tar.

2. Their colour is usually brown or black.

3. They have a peculiar smell, or at least acquire it when rubbed. This smell is known by the name of bituminous odour.

4. They become electric by friction, though not insulated.

5. They melt when heated, and burn with a strong smell, a bright flame, and much smoke.

6. They are insoluble in water and alcohol, but are commonly soluble in ether and the fixed and volatile oils.

7. They do not combine with alkaline leys, nor form soaps.

8. Acids have little action on them; the sulphuric scarcely any; the nitric, by long and repeated digestions, dissolves them, and converts them into a yellow substance, soluble both in water and alcohol, and similar to the product formed by the action of nitric acid on resins.

There are three bitumens, namely, asphaltum, mineral tar, and mineral caoutchouc.

Asphaltum is solid, and is found abundantly in a lake in Trinidad, in Albania, and on the shores of the Dead Sea. It was one of the principal ingredients in the celebrated Greek fire so much employed in the middle ages.

Mineral tar is nothing else than asphaltum softened by petroleum.

Mineral caoutchouc is found in Derbyshire, and is named from the great resemblance which it has to Indian rubber or common caoutchouc. It is soft and elastic, but in other respects possesses the characters of asphaltum.

Pit coal, so abundant in this country, and constituting so valuable a portion of our mineral riches, is intimately connected with bitumen. Hardly any doubt can be entertained that it is of vegetable origin, though it must have been deposited before the present race of inhabitants existed on the earth. There are five different kinds of pit coal which exist in Great Britain. They have been distinguished by the following names:

1. Kilkenny coal.

2. Caking coal.

3. Splint coal.

4. Cherry coal.

5. Cannel coal.

1. Kilkenny coal has a semimetallic lustre, is black, and does not soil the fingers. Its specific gravity is 1*4354. It consumes without flame, and leaves about four per cent, of light-brown ashes, composed principally of silica and iron. It consists of about thirty-five atoms of carbon united to two atoms of oxygen.

2. Caking coal is so called because when heated it melts into a kind of bituminous mass, in consequence of which all the pieces of coal, however small, adhere together into a cake. Its colour is velvet black, its lustre shining and resinous. Soft and very easily frangible. Fragments cubical. Brittle. Soils the fingers. Specific gravity 1∙269. It catches fire very readily, and burns with a lively yellow flame. Its constituents appear to be 33 atoms carbon, 11 atoms hydrogen, 3 atoms azote, and 1∙5 atom oxygen.

3. Splint coal occurs abundantly in the neighbourhood of Glasgow, constituting the fifth of the six Glasgow beds. Colour brownish-black. Lustre glistening, resinous. Not harder than caking coal, but much more difficultly frangible. Fragments wedge-shaped. Specific gravity 1∙290. It requires a higher temperature to kindle it than caking or cherry coal. It burns with flame, and is very durable. Its constituents seem to be 28 atoms carbon, 14 atoms hydrogen, 1 atom azote, and 3∣ atoms oxygen.

4. Cherry coal abounds in the neighbourhood of Glasgow and in Staffordshire. Colour velvet-black. Lustre splendent or shining, resinous. Does not melt nor cake. λ 7 cry easily frangible. Specific gravity 1∙265. When exposed to heat it readily catches fire, burns with a clear yellow flame, giving out much heat, but not lasting long. Its constituents appear to be 34 atoms carbon, 34 atoms hydrogen, 2 atoms azote, and 1 atom oxygen.

5. Cannel coal is so called because it burns like a candle when lighted, and is often employed as a substitute for candles. It abounds at Wigan, occurs near Coventry, in the Marquis of Anglesey’s park, is found in Ayrshire, and at Lesmahago in Lanarkshire. Colour dark-grayish black. Lustre glistening, resinous. Does not stain the fingers. Admits of a good polish, and is often cut into ornaments like jet. Fragments sometimes cubic, sometimes wedge-shaped, and sometimes amorphous, but most commonly sharp edged. About as hard as caking coal. Brittle. Not nearly so easily frangible as caking and cherry coal, but more easily than splint coal. Specific gravity 1∙272. Its constituents appear to be 11 atoms carbon, 22 atoms hydrogen, and 1 atom azote. Of these five kinds of coal, the best for coking is Kilkenny coal, or Welsh culm, which seems to agree with it. Caking coal comes next, and cannel coal is the worst of all.

DIVISION III.—OF SECONDARY COMPOUNDS.

By secondary compounds is meant the compounds formed by the union of the primary compounds with each other. Now, as the neutral primary compounds enter into but few combinations, it is obvious that the secondary compounds must consist chiefly of combinations of the acids with bases. Such compounds are called salts. They constitute a very'· numerous and important set of bodies, which it is of great consequence to understand well.

The word salt was originally confined to common salt, a substance which was known and in common use from the remotest ages. It was afterwards generalized by chemists, and employed by them in a very extensive and not very definite sense. Every body which is sapid, easily melted, soluble in water, and not combustible, was called a salt.

In process of time the term salt was restricted to three classes of bodies; namely, acids, alhalies, and the compounds which acids form with alkalies, earths, and metallic oxides. The first two of these classes were called simple salts. The salts belonging to the third class were called compound or neutral. This last appellation originated from an opinion that acids and alkalies, of which they are composed, were of a contrary nature, and that they counteracted one another, so that the resulting compounds possessed neither the properties of acids nor of alkalies, but properties intermediate between the two.

The term salt is now still further restricted. Acidsand alkalies are no longer considered as salts. The term is applied only to the combinations of acids with alkalies, earths, and metallic oxides. Now as there are nine classes [7:6:445] of acids, it is obvious that there must be as many different classes of salts.

CLASS I.—OXYGEN ACID SALTS.

This class of salts has been longest known and most completely investigated; of course the salts belonging to it are by far the most numerous. The genera of these salts are named from their acids. Thus, if the acid which a salt contains be the sulphuric, it is called a sulphate, if it be nitric, it is called a nitrate, and so on. The species are distinguished from each other by adding the name of the base. Thus sulphate of soda is a salt composed of sulphuric acid and soda; oxalate of lime is a salt composed of oxalic acid and lime. When the salt is a compound of one atom of acid and one atom of base, it is distinguished simply by its name. If the salt contains two atoms of acid united to one atom of base, the Latin numeral bis or bi is prefixed. Thus bisulphate of potash is a salt composed of two atoms of sulphuric acid and one atom of potash. When there are three, four, &c. atoms of acid, the numeral adverbs ter, quater, &c. are prefixed. Thus qziateroxalate of potash means a compound of four atoms of oxalic acid and one atom of potash. When there exists a compound of an atom and a half of acid united to one atom of base, the Latin term sesqui (one and a half) is prefixed. Thus sesquicarbonate of soda is a compound of one and a half atom of carbonic acid and one atom of soda.

When there exists a combination of two atoms of base with one atom of acid, this is denoted by prefixing the Greek numeral adverb dis. Thus diphosphate of potash means a compound of two atoms of potash with one atom of phosphoric acid. The prefixed ⅛⅛ tetrahis, &c. indicate three, four, &c. atoms of base with one atom of acid.

The arranging of the salts according to the bases is attended with such considerable advantage that it has been generally adopted by modern chemists. Now there arc fifty-one bases known to be capable of combining with acids. If therefore we divide the oxygen acid salts according to their bases, we shall have fifty-one genera. A minute description of all the salts belonging to these genera, which are very numerous, would be inconsistent with the limits to which an article of this kind ought to extend. We refer the reader who wishes for a detailed description of each of these bodies, so far as they have been examined, to the second volume of Dr Thomson’s work on the Chemistry of Inorganic Bodies, where they occupy no less a space than 566 closely printed pages. Here we shall give the characters of the different genera, and point out the number of each which have been examined; for it is scarcely necessary to observe, that in consequence of the difficulty of procuring various acids and bases, many of the saline substances have been hitherto but superficially examined.

Genus 1. Salts of Ammonia.

The salts of ammonia, with a very few exceptions, are all soluble in water.

1. When potash or lime is mixed with an ammoniacal salt, a smell of ammonia is emitted.

2. If to an ammoniacal salt dissolved in water a little solution containing magnesia be added, and afterwards some phosphate of soda dropt in, a white precipitate falls.

3. When an ammoniacal salt is exposed to heat it is completely dissipated in vapours, except when the acid has a fixed metal, or phosphorus, or boron, for its base, in which case the acid alone remains behind, the ammonia being dissipated.

4. The ammoniacal salts are not precipitated by infusion of nutgalls or prussiate of potash.

5. When a solution of chloride of platinum is dropt into an ammoniacal salt, a yellow-coloured precipitate falls in very small crystals.

This genus of salts has been long known, and pretty completely investigated. The number of ammoniacal salts at present known amount to seventy-seven. Besides these, there arc sixty-eight double salts containing ammonia. Thus the whole ammoniacal oxygen acid salts at present known, single and double, amount to 145.

Genus 2. Salts of Potash.

The salts of potash, a very few excepted, are soluble in water; but in general they are less soluble than those of ammonia.

1. Many of them can be obtained in the state of crystals, but a number of them likewise refuse to crystallize. In general they have a less tendency to form regular crystals than the salts of soda.

2. If tartaric acid dissolved in water be dropt into an aqueous solution of a salt of potash, the liquid speedily deposits a white granular sediment. This sediment has a sour taste, and consists of small crystals of cream of tartar, or bitartrate of potash.

3. If a solution of sulphate of alumina be dropt into a salt of potash, octahedral crystals of alum are soon deposited.

4. The salts of potash may be exposed to a red heat without being volatilized like the salts of ammonia. If the acid contained in the salt be combustible, it is decomposed, and carbonate of potash, mixed with a little charcoal, remains behind. If the acid is not combustible the salt usually fuses, and its nature is not altered, though to this there are some exceptions. Thus the nitric acid is gradually decomposed at a red heat, sulphurous acid lets sulphur sublime, phosphorous acid allows phosphuretted hydrogen to escape, and chloric acid gives out abundance of oxygen gas.

5. The salts of potash are not precipitated by infusion of nutgalls, nor by prussiate of potash.

6. They are not affected by sulphuretted hydrogen gas, nor by the addition of a sulphohydrate, except when their acid contains a metal for its base, in which case the acid may be decomposed and precipitated, and the potash left behind.

7. When a solution of chloride of platinum is dropt into a salt of potash, an orange, or yellow-coloured precipitate falls.

Sulphate of alumina and chloride of platinum are precipitated likewise by salts of ammonia. We must therefore, in order to know whether a salt so precipitated contains ammonia or potash for its base, expose it to a red heat. If it be an ammoniacal salt, it will be dissipated or decomposed, leaving the acid (if fixed); but a potash salt will either not be altered, or it will leave potash, usually in the state of carbonate, behind.

A salt with base of potash may be distinguished by the blowpipe in the following manner: Fuse before the blowpipe a little borax to which a small portion of oxide of nickel has been added. A yellowish glass is obtained. Fuse this bead with a little of the salt under examination. If it contain potash the bead will assume a bluish colour.

The salts of potash known and described amount to ninety-nine, besides, eighty-three double salts into which potash enters as a constituent. Thus the potash salts at present known and examined amount to 182.

Genus 3. Salts of Soda.

In general the salts of soda are much more soluble in water than the corresponding salts of potash. Many of the salts of potash contain no water of crystallization, but [7:6:446] the greater number of the soda salts contain a good deal of water.

1. When exposed to a red heat they usually speedily melt into a liquid, in consequence of the great quantity of water which they contain. If the heat be continued, the water is driven off, and the salt converted into a white powder. When the heat is further urged, if the acid be of a combustible nature it is destroyed; if it be volatile it is driven off; but if it be fixed the salt melts again at a red heat, and continues in a liquid state as long as the temperature is kept up. The salt on cooling is in the state of an opaque white mass, and is usually destitute of water.

2. No precipitate is produced in salts of soda by tartaric acid or chloride of platinum; nor does sulphate of alumina when added occasion the precipitation of octahedral crystals of alum; nor is any precipitate produced by infusion of nutgalls or prussiate of potash, except when the basis of the acid happens to be a metal.

3. One of the easiest methods of determining whether the base of a given salt be potash or soda, is to determine the shape of the crystals which it forms. If it does not shoot into regular crystals, separate the acid by means of sulphuric or nitric acid, and let the new-formed salt crystallize. Sulphate of potash crystallizes in right rhombic prisms; but commonly from truncations it puts on the form of a pyramidal dodecahedron composed of two sixsided pyramids applied base to base. Sulphate of soda crystallizes in oblique, rhombic prisms; but it is usually in long six-sided prisms longitudinally striated. Sulphate of potash when exposed to the air undergoes no change, but sulphate of soda soon falls to powder. Nitrate of potash crystallizes in long six-sided prisms, but nitrate of soda in rhomboids, the faces of which meet at angles of 106° 30' and 73° 30'.

The salts of soda known and described amount to ninety-one, besides twenty-six double salts into which soda enters as a constituent; thus the whole soda salts at present known amount to 117.

Genus 4. Salts of Lithia.

Lithia has been known only for a short time, and is scarce. This is the reason why its salts have been but superficially examined.

1. They are all soluble in water (as far as is known), and in this respect resemble the salts of potash and soda. But the carbonate of lithia is much less soluble than either the carbonate of potash or of soda.

2. When carbonate of potash is dropt into a concentrated solution of a salt of lithia, a white precipitate falls. This precipitate maybe dissolved again by diluting the liquid with a sufficient quantity of water, or by raising it to the boiling point.

3. Chloride of platinum occasions no precipitate when dropt into a salt of lithia.

4. Several of the salts of lithia melt at a very low temperature.

5. When the salts of lithia are heated to redness in a platinum vessel, they act with considerable energy upon that metal.

6. Neither prussiate of potash nor infusion of nutgalls occasion any precipitate in the salts of lithia.

7. Salts of lithia are not precipitated by caustic potash.

8. If to a salt of lithia we add a quantity of phosphate of soda, and evaporate, the solution becomes muddy. If we evaporate to dryness, and pour water on the residue, a white powder remains undissolved, which falls slowly to the bottom of the vessel.

9. When an alcoholic solution of a lithia salt is set on fire, it burns with a purple-red colour.

10. If we mix together one part of fluor spar and one and a half part of sulphate of ammonia, and add to the mixture a little of any lithia salt, and heat before the blowpipe, the flame has at first a green colour; but when the mixture fuses the colour of the flame becomes purple red.

The oxygen acid salts of lithia hitherto examined and described are only seventeen; and only two of them, the sulphate and carbonate, have been subjected to analysis.

Genus 5. Salts of Barytes.

A considerable number of the salts of barytes are insoluble in water. Indeed, if we except the nitrate and acetate, and a few other salts with vegetable acids, most of the salts of barytes are insoluble.

1. They are white or transparent, and generally affect a crystalline form.

2. If a little solution of sulphate of soda be let fall into a salt of barytes, dissolved in water, a white precipitate falls, which is insoluble in nitric acid.

3. When heat is applied to a salt of barytes it is not completely dissipated. If the acid be combustible, carbo nate of barytes remains behind; if the acid is neither combustible nor volatile, the salt continues undecomposed.

4. Prussiate of potash occasions no precipitate when dropt into a salt of barytes, unless the acid happen to contain a metallic base. The same remark applies to sulphohydrate of potassium.

5. The salts of barytes are poisonous.

6. When a fusible salt of barytes is heated before the blowpipe it tinges the flame yellow. The same coloured flame appears when alcohol containing a soluble salt of barytes is burnt.

7. Oxalate of ammonia, when dropt into a solution of a barytes salt, does not occasion an immediate precipitate.

T he salts of barytes which have been examined and described amount to eighty-seven, besides two double salts into which it enters as a constituent; making the whole barytes salts at present known eighty-nine.

Genus 6. Salts of Strontian.

The salts of strontian are in general more soluble than those of barytes, but less soluble than the salts of lime.

1. The greater number of them are capable of assuming a crystalline form, though they are not more given to crystallize than the salts of barytes.

2. Solutions of strontian arc prccipitated by the sulphates, phosphates, and oxalates; but oxalate of ammonia does not occasion an immediate precipitate when dropt into a salt of strontian.

3. We can distinguish a salt of strontian from a salt of barytes by means of succinate of ammonia. When we drop this salt into a neutral solution of strontian no precipitate falls, but a precipitate immediately appears if we drop it into a solution of a neutral salt of barytes.

4. When a piece of paper dipt into a solution of a salt of strontian is set on fire, it burns with a red flame; but if it be dipt into a salt of barytes, it burns with a yellow flame.

5. When a current of fluosilicic acid gas is passed through a solution of strontian in muriatic acid, no precipitate falls; but when the same gas is passed through a solution of barytes, a precipitate immediately falls.

6. Salts of strontian are not precipitated by prussiate of potash nor sulphohydrate of potassium, unless the acid happens to have a metallic base.

7. Salts of strontian are not poisonous.

The number of oxygen acid salts of strontian which have been examined and described amount to fifty, and eighteen of these have been subjected to analysis. Only one double [7:6:447] salt containing strontian has been yet noticed, namely, strontian hyposulphite of silver, which was formed by Herschell.

Genus r l. Salts of Lime. A considerable number of the salts of lime are insoluble in water. Some of those which are soluble cannot easily be crystallized. When a salt of lime is insoluble in water, if we boil it for some time in a solution of carbonate of potash, a white powder remains, which is soluble, with effervescence, in nitric acid, and which possesses all the characters of carbonate of lime.

1. The soluble salts of lime are not altered by the addition of pure ammonia, but the addition of potash or soda occasions the precipitation of a white matter, which is pure lime.

2. When oxalate of ammonia is dropt into a salt of lime, a dense white precipitate immediately begins to make its appearance; but citrate or tartrate of ammonia does not occasion an immediate precipitate, though racemate of ammonia does.

3. The salts of lime are not precipitated by prussiate of potash; but some of them are precipitated when infusion of nutgalls is mixed with them.

The salts of limc hitherto examined and described amount to seventy-five, besides fifteen double salts containing lime as a constituent, making altogether ninety calcareous salts at present known.

Genus 8. Salts of Magnesia.

A great proportion of the salts of magnesia are soluble in water, and capable of crystallizing.

1. When any of the fixed alkalies or their carbonates is dropt into a salt of magnesia, a white flocky precipitate falls.

2. No precipitate appears when sulphate of soda is dropt into a salt of magnesia, because sulphate of magnesia is a very soluble and crystallizable salt.

5. If phosphate of soda be dropt into a salt of magnesia, no precipitate appears; but if any ammonia be added, a white precipitate falls, which is a double salt, composed of phosphoric acid, magnesia, and ammonia. This precipitate furnishes the best method yet discovered for detecting the presence of magnesia, and even for separating it from other bodies.

4. Prussiate of potash occasions no precipitate in a salt of magnesia, unless the acid happen to have a metal for its base.

5. Magnesia has a great tendency to enter into double combinations, especially with ammonia and potash.

6. When a salt of magnesia is tinged with a little nitrate of cobalt, and fused before the blowpipe with a strong blast, it assumes a fine flesh colour, the tint of which is very feeble, and not easily distinguished till the assay is perfectly cold. When the acid of the salt is combustible or volatile, we are not able to accomplish the fusion of it before the blowpipe; in such cases we must add borax or biphosphate of soda.

The salts of magnesia which have been examined and described amount to forty-nine; of these, twenty have been subjected to analysis. There arc likewise fourteen double salts known which contain magnesia; so that the whole magnesian salts at present known amount to sixty-three.

Genus 9. Salts of Alumina.

Most of the salts of alumina are soluble in water, but few of them are capable of crystallizing.

1. They are distinguished by a sweet and astringent taste. In this respect they resemble the salts of glucina, yttria, and chromium, though they are much less sweet; and the salts of chromium want the astringency which characterizes the aluminous salts.

2. They are not precipitated by oxalate of ammonia nor tartaric acid, which sufficiently distinguishes them from salts of yttria.

3. They are not precipitated by prussiate of potash nor by tincture of nutgalls, in which respect they differ both from salts of yttria and of glucina.

4. Phosphate of ammonia, when dropt into an aluminous salt, occasions a white precipitate.

5. Hydriodate of potash occasions a white flocky precipitate in a solution of alumina, which speedily becomes yellow, and continues permanent. This is not owing to the excess of acid which the salts of alumina usually contain; for the yellow colour does not disappear on the addition of carbonate of ammonia.

6. If sulphuric acid, and then sulphate of potash, be added to a salt of alumina, and the liquid be set aside, octahedral crystals of alum soon make their appearance in it.

7. When nitrate of cobalt is mixed with a mineral containing alumina, and the mixture is exposed to the action of the blowpipe, it acquires a fine blue colour, which becomes deeper without altering its nature on the addition of more cobalt. This colour is only seen distinctly by daylight, and after the assay is cold. This method of proceeding may be followed with most of the salts of alumina.

8. Most of the salts of alumina are decomposed by a red heat, the acid being dissipated and the alumina left. The only exceptions consist of those salts which contain a fixed acid, as borate, phosphate, tungstate, &c.

The salts of alumina which have been examined and described amount only to thirty-nine; of these, eleven have been subjected to analysis. There are also eleven double salts containing alumina. Thus the whole aluminous salts at present known amount to fifty.

Genus 10. Salts of Glucina.

Glucina is so scarce a substance that its salts have been examined very imperfectly.

1. They are much more soluble in water than the corresponding salts of yttria, and a smaller number of them seem susceptible of crystallizing.

2. They are not precipitated by oxalate of ammonia or tartrate of potash, which sufficiently distinguishes them from salts of yttria.

3. Prussiate of potash occasions a white precipitate when dropt into a solution of a salt of glucina.

4. Infusion of nutgalls occasions a yellowish precipitate, which acquires a purplish tint if any iron be present.

5. The sulphate of glucina does not crystallize, nor do crystals of alum form in it when sulphate of potash 'is mixed with the solution.

6. When a salt of glucina is mixed with a little nitrate of cobalt, and exposed to the action of the blowpipe, it becomes black or dark-gray.

The salts of glucina at present known and described amount to only nineteen. Of these, only the four sulphates have been subjected to analysis. Only two double salts containing glucina have been noticed; namely, the ammonia carbonate of glucina and the sulphochromate of glucina. Genus 11. Salts of Yttria.

The greater number of the salts which yttria forms with acids remain unknown, in consequence of the great scarcity of that substance.

1. A considerable proportion of the salts of yttria are insoluble in water, and have not therefore been obtained in the state of crystals.
[7:6:448]

2. Yttria maybe precipitated from its solutions in acids by phosphate of soda, carbonate of soda, oxalate of ammonia, and tartrate of potash.

3. It is precipitated also in a white chalky state by. prussiate of potash.

4. The alkaline carbonates throw down a white precipitate when dropt into solutions of yttria in acids; but the precipitate is redissolved by adding an excess of the carbonate. In this property yttria agrees with glucina.

5. The salts of yttria have fully as sweet a taste as those of glucina, but they are also astringent. The taste is nearly similar to a mixture of a solution of alumina and glucina.

The salts of yttria known and examined amount only to seventeen. Of these, nine have recently been analysed by Dr Steel, in the laboratory of the professor of chemistry in the University of Glasgow. There are likewise five double salts into which yttria enters. Thus all the yttria salts yet known are only twenty-two.

Genus 12. Salts of Protoxide of Cerium.

These salts, which, from the scarcity of cerium, have been but imperfectly examined, possess the following characters:

1. They have a light flesh-red colour, or arc sometimes nearly white.

2. Their solution in water has a sweet taste.

3. Sulphohydrate of potassium occasions only a white precipitate, consisting of the oxide of cerium. Sulphuretted hydrogen gas occasions no precipitate.

4. Prussiate of potash occasions a snow-white precipitate, soluble in nitric and muriatic acids.

5. Gallic acid, and the infusion of nutgalls, occasion no precipitate.

6. Oxalate of ammonia occasions a white precipitate, which is soluble in nitric and muriatic acids.

7. Arseniate of potash, when dropt into a solution of protoxide of cerium, occasions a white precipitate. Tartrate of potash occasions no precipitate.

The salts of protoxide of cerium hitherto examined amount to eighteen. Of these, eight have been analysed by Dr Steel. There are likewise five double salts into which protoxide of cerium enters. Thus the salts of protoxide of cerium at present known amount to twenty-three, Gemis 13. Salts of Peroxide of Cerium.

These salts are very imperfectly investigated indeed. They are distinguished by a yellow or orange colour, but in other respects probably agree nearly in characters with the last genus of salts. Only seven salts belonging to this genus are known; and of these, four have been subjected to analysis by Dr Steel.

Genus 14. Salts of Zirconia.

Zirconia dissolves in acids only when newly precipitated and still moist. If it be dried, and especially if it be subjected to a red heat, it is acted on by acids with great difficulty.

1. The alkalies, the alkaline earths, and the earths proper, separate zirconia from all its combinations with acids.

2. The greater number of the salts of zirconia are insoluble in water. This is the case with the sulphate, sulphite, phosphate, fluate, borate, carbonate, selenite, oxalate, tartrate, citrate, mucate, and gallate. The muriate, nitrate, acetate, benzoate, and malate, are soluble in water.

3. They have an astringent, harsh, and disagreeable taste, similar to some of the metalline salts.

4. When sulphuric acid is dropt into a salt of zirconia, a white precipitate falls.

5. When carbonate of ammonia is dropt into a salt of zirconia, a white precipitate appears, which is redissolved, if an additional quantity of carbonate of ammonia be added.

6. Oxalate of ammonia and tartrate of potash occasion white precipitates when dropt into a salt of zirconia.

7. Prussiate of potash throws down nitrate of zirconia white.

8. Chromate of potash occasions a yellow precipitate.

9. The infusion of nutgalls, when dropt into a solution of zirconia, occasions a white precipitate. The sulphohydrate of potassium occasions no precipitate if the solution be free from iron.

The salts of zirconia hitherto examined amount to sixteen. Of these, only the three sulphates have been subjected to analysis. Three double salts containing zirconia are also known; thus making a total of nineteen salts of zirconia, most of which have scarcely been examined except as to colour and solubility.

Genus 15. Salts of Protoxide of Iron.

These salts, some of which have been long known and much employed, possess the following characters:

1. The greater number of them are soluble in water, and in general the solution has a greenish colour at first, but soon becomes yellow when left exposed to the air.

2. Prussiate of potash occasions a light-blue or even white precipitate when dropt into them; but it speedily becomes blue, and the intensity of the. shade deepens rapidly when it is left exposed to the air.

3. Sulphohydrate of potassium throws down a black precipitate. Sulphuretted hydrogen renders the solution nearly colourless, but occasions no precipitate.

4. Gallic acid, or the infusion of nutgalls, occasions a black or deep-blue or purple precipitate, at least if the solution be in contact with the air.

5. Phosphate of soda occasions a white precipitate.

6. Benzoate of ammonia does not precipitate the protosalts of iron; but if they be heated with nitric acid, and then neutralized, it throws them down light yellow. The action of succinate of ammonia is quite similar.

The salts of protoxide of iron hitherto formed and examined by chemists amount to thirty-eight. Of these, ten species have been subjected to analysis. There are likewise nine double salts known which contain the protoxide of iron. Thus all the salts of protoxide of iron with which we are at present acquainted amount to forty-seven.

Genus 16. Salts of Peroxide of Iron.

The aqueous solution of these salts has usually a red or yellowish-red colour. They have a sweetish, astringent, and very harsh taste. The greater number of them are incapable of crystallizing. Of those that crystallize, some form colourless (when they contain much water), and some red-coloured crystals. In general they are soluble in alcohol. They are precipitated of a very dark blue, almost black, by prussiate of potash. Their other characters correspond with those of the last genus.

The salts of peroxide of iron hitherto examined amount to forty-three. Of these, fourteen have been analysed with more or less accuracy. There are twelve double salts known which contain peroxide of iron. Thus the salts of peroxide of iron at present known amount to fifty-five.

Genus 17. Salts of Protoxide of Manganese.

Most of these salts are soluble in water. The solutions are colourless, or nearly so; but the crystals, when the salts arc capable of crystallizing, have a beautiful fleslι-red tint. This is most beautiful in the sulphate and acetate. In the tartrate and racemate the shade is so deep [7:6:449] that the salt appears red. They have usually a saline and bitter taste, something like that of Glauber salt.

1. When a fixed alkali is dropt into a solution of protoxide of manganese in an acid, a white precipitate falls, which gradually becomes black by exposure to the air.

2. Prussiate of potash throws down a white precipitate.

3. Sulphohydrate of potassium throws down a yellow precipitate. Sulphuretted hydrogen gives the solution a white colour, but occasions no precipitate unless the acid in the solution be weak.

4. Gallic acid and the infusion of nutgalls occasion no precipitate.

5. Manganese is not precipitated in the metallic state by any other metal.

6. The salts of manganese are not precipitated by succinate or benzoate of ammonia.

7. When chloride of soda is dropt into a solution of protoxide of manganese, the manganese is thrown down black and very bulky. This precipitate consists of deutoxide of manganese. Chloride of lime also throws down manganese in the state of deutoxide, but it is combined with a portion of lime.

8. Ammonia throws down a white precipitate, which gradually becomes black if air have access to it. If we add some sal ammoniac to the solution, ammonia becomes incapable of throwing down the protoxide of manganese. A solution of sal ammoniac immediately dissolves the precipitate thrown down by ammonia; but on leaving the liquid exposed to the air the precipitate again appears.

9. When a salt of manganese is heated before the blowpipe with carbonate of soda, it fuses into a green glass, which becomes bluish green when cold. With borax in the oxydizing flame it forms an amethyst-coloured glass, but in the reducing flame the colour disappears.

The salts of protoxide of manganese at present known amount to thirty-seven. Of these, thirteen have been analysed. Only three double salts containing protoxide of manganese are known. These raise the number of salts of protoxide of manganese to forty.

Genus 18. Salts of Sesquioxide of Manganese.

These salts have a reddish colour, and cannot be crystallized, nor even obtained in a solid state. They are only known in solution, and always contain a great excess of acid. Only six such salts have been hitherto described, the sulphate, nitrate, oxalate, carbonate, tartrate, and citrate.

Genus 19. Salts of Protoxide of Nichel.

The soluble salts of nickel have a beautiful emeraldgreen colour; while that of the insoluble salts is usually light green, and in some cases leek green.

1. Prussiate of potash, when dropt into a solution of a salt of nickel, throws down a milk-white precipitate.

2. Sulphohydrate of potassium throws down a black precipitate, which is a sulphurct of nickel. Sulphuretted hydrogen gas occasions no precipitate.

3. Gallic acid and the infusion of nutgalls occasion no precipitate, at least in the sulphate of nickel.

4. The ammoniacal solution of oxide of nickel has a blue colour.

5. Potash throws down an apple-green precipitate, not re-dissolved by adding an excess of the alkali.

6. Carbonate of ammonia throws down an apple-green precipitate, re-dissolved in an excess of the carbonate, rendering the liquid bluish-green.

7. The greater number of the salts of nickel, when heated with boron before the blowpipe, fuse into an orange-yellow or reddish glass, which becomes yellow, or almost colourless, on cooling. When the proportion of salt of nickel is considerable, the glass is opaque and of a dull brown while in fusion; but on cooling it becomes dull red and transparent.

The salts of nickel which have been prepared and examined are only twenty-eight, about twelve of which have been subjected to analysis. There arc also nine double salts of nickel known; so that the whole nickel salts hitherto investigated amount to thirty-seven.

Genus 20. Salts of Protoxide of Cobalt.

The greater number of the salts of cobalt are soluble in water, and have a red colour.

1. The alkalics, when dropt into solutions of these salts, throw down a blue-coloured precipitate, or reddish brown if the solution contain arsenic acid.

2. Prussiate of potash occasions a light-green precipitate.

3. Sulphohydrate of potassium occasions a black precipitate, soluble again if the sulphohydrate be added in excess. Sulphuretted hydrogen gas occasions no precipitate in these solutions.

4. Gallic acid occasions no change, but the infusion of nutgalls throws down a yellowish-white precipitate.

5. The ammoniacal solution of oxide of cobalt has the colour of port wine. It is not immediately precipitated by prussiate of potash, but after some time a reddish precipitate falls.

6. The salts of cobalt are not precipitated by the hydriodate of zinc.

7. Cobalt is not precipitated from any of its soluble salts by a plate of zinc.

8. Carbonate of ammonia throws down a red precipitate which is soluble in sal ammoniac.

9. The greater number of the salts of cobalt, when fused before the blowpipe with borax, form a transparent blue-coloured bead.

The salts of cobalt hitherto described and examined amount to twenty-four, of which there are eleven which have been subjected to analysis. There arc also five double salts known into which cobalt enters as a constituent; so that the whole cobalt salts at present known amount to twenty-nine.

Genus 21. Salts of Oxide of Zinc.

Almost all the acids act with considerable energy on zinc. Hence the salts of this metal arc easily formed; and as there is only one oxide of zinc, they are not liable to change their state, like the salts of protoxide of iron and protoxide of tin.

1. The greater number of them are soluble in water, and the solution is colourless and transparent. Many of their solutions, when properly concentrated, deposit the salt of zinc which they contain in crystals.

2. Prussiate of potash occasions a white gelatinous precipitate when dropt into aqueous solutions of salts of zinc.

3. Sulphohydrate of potassium and sulphuretted hydrogen throw down a white precipitate.

4. Gallic acid and the infusion of nutgalls occasion no precipitate when dropt into these salts.

5. Potash occasions a white gelatinous precipitate, which is readily dissolved by sulphuric or muriatic acid, and by an excess of potash. Ammonia behaves in the same manner.

6. Zinc is not precipitated in the metallic form from solutions of its salts by any other metal whatever.

7. Sulphocyanate of potash and hydriodate of potash occasion white precipitates when dropt into a solution of a salt of zinc.

8. Carbonate of potash throws down a white precipitate, [7:6:450] not soluble in the excess of the carbonate; but it may be dissolved by potash or ammonia.

9. When a zinc salt is heated before the blowpipe on charcoal, after the acid is destroyed or dissipated, the residual oxide of zinc-being reduced, gives out a brilliant light, and is gradually dissipated before the reducing flame; a white vapour at the same time condensing on the surface of the charcoal.

The salts of zinc hitherto examined and described amount to forty-four, of which nineteen species have been subjected to analysis. There are likewise six double salts which contain zinc as a constituent. Thus the salts of zinc at present known amount to fifty.

Genus 22. Salts of Oxide of Cadmium.

Cadmium being a scarce metal, and but recently discovered, the salts of its oxide have not been very carefully studied. A considerable number of them are soluble in water. The aqueous solutions are colourless, or have a very slight shade of yellow. The insoluble salts are white powders.

1. When a fixed alkali is dropt into a solution of a salt of cadmium, the oxide is precipitated in the state of a white hydrate, which is not again redissolved by adding an excess of the alkali.

2. Ammonia likewise precipitates it in the state of a white hydrate. The precipitate is again redissolved when an excess of ammonia is added.

3. The alkaline carbonates throw down cadmium in the state of a white carbonate. This carbonate does not form a hydrate, as is the ease with the carbonate of zinc. Neither is it redissolved by the addition of an excess of carbonate of ammonia, as is the case with the carbonate of zinc, unless there existed a notable excess of acid in the solution before the addition of the carbonate of ammonia.

4. Phosphate of soda throws down cadmium in the state of a white powder, while zinc is thrown down by the same precipitant in the state of crystalline scales.

5. Sulphuretted hydrogen and the sulphohydrates precipitate cadmium yellow or orange. This precipitate resembles orpiment, but may be distinguished by the facility with which it dissolves in muriatic acid, and by its bearing a red heat without being altered.

6. Prussiate of potash occasions a white precipitate when dropt into a salt of eadmium.

7. Infusion of nutgalls does not occasion any precipitate.

8. When a plate of zinc is put into a solution of a salt of eadmium, the eadmium is precipitated in dendritical crystals, and in the metallic state.

The salts of cadmium hitherto described and examined amount to fifteen. Of these, twelve have been analysed. There is also one double salt, namely, the potash sulphate of cadmium, making the whole cadmium salts at present known amount to sixteen.

Genus 23. Salts of Protoxide of Lead.

A considerable number of these salts are not soluble in water unless when they contain an excess of acid. These before the blowpipe, on charcoal, yield readily a button of lead. The solutions of those that are soluble are transparent and colourless, and are distinguished by a sweet and astringent taste.

1. Prussiate of potash occasions a white precipitate when dropt into a solution of a salt of lead.

2. Sulphohydrate of potassium occasions a black precipitate. A similar precipitate is thrown down by sulphuretted hydrogen.

3. Gallic acid and the infusion of nutgalls occasion a white precipitate.

4. When a plate of zinc is put into a solution of a salt of lead, the lead is most commonly thrown down in leaves in the metallic state. Sometimes it falls in the state of a white powder.

5. When potash is dropt into a solution of a salt of lead, a white precipitate falls, which is redissolved on adding an excess of the alkali.

6. When chromate of potash is dropt into a solution of lead, a beautiful orange-coloured precipitate falls. When this powder is digested in caustic potash it assumes a fine scarlet colour.

7. When sulphate of soda is dropt into a solution of lead, a white precipitate falls.

The salts of lead which have been formed and examined with more or less accuracy amount to eighty-eight, and of these no fewer than fifty-one have been subjected to analysis. Not above five double salts containing protoxide of lead are at present known. Doubtless many others might be formed, though hitherto they have escaped the researches of chemists.

Genus 24. Salts of Protoxide of Tin.

The salts of tin have not been subjected to a rigid examination by chemists. The examination is attended with difficulties, and contains nothing very attractive. The protoxide has the strongest affinity for acids, though both oxides have the property of combining with acids and forming salts.

1. Several of the salts of protoxide of tin are insoluble in water, and can therefore be obtained only in the state of white powders. Those that dissolve in water are white, the solutions are colourless, and have an astringent, harsh, and metallie taste. When in solution they rapidly absorb oxygen, and are converted into the corresponding persalts.

2. When a plate of zinc is put into a solution of a salt of tin, the tin is thrown down in the metallic state in fine thin plates.

3. Prussiate of potash occasions a white gelatinous precipitate.

4. Sulphohydrate of potassium occasions a coffee-brown precipitate.

5. Neither gallic acid nor the infusion of nutgalls occasions any precipitate.

6. When chloride of gold is dropt into a dilute solution of a salt of protoxide of tin, a purple, or at least a reddish-brown precipitate falls. For the formation of the beautiful colour called purple of Cassius, both the protoxide and peroxide of tin ought to be in the solution.

7. A solution of potash throws down a white precipitate, which dissolves in an excess of the alkali. If the solution be boiled, a black powder falls, which is metallic tin, while a compound of peroxide of tin and potash remains in solution.

8. Ammonia throws down a white precipitate, not soluble in an excess of ammonia.

9. The solutions of protoxide of tin redden litmus paper. The salts of protoxide of tin hitherto formed and examined amount to twenty-three. Hardly any of them have been subjected to a rigid analysis. Few double salts of tin are known, excepting those which contain chlorides of that metal.

Genus 25. Salts of Peroxide of Tin.

These salts in many of their characters resemble those of the last genus, but they are united by a weaker affinity, and few or none of them can be exhibited in the state of crystals.

1. Potash dropt into a solution of a salt of peroxide of tin throws down a white precipitate, soluble in an excess of the alkali; but no black powder appears on boiling.

2. Ammonia throws down a white precipitate, which is soluble in a great excess of ammonia.
[7:6:451]

3. Prussiate of potash occasions no immediate precipitate; but after some time the whole congeals into a stiff, yellow jelly, which is insoluble in muriatic acid.

4. Sulphohydrate of ammonia throws down a yellow precipitate, and redissolves by adding an excess of the precipitants. Sulphuretted hydrogen produces no immediate effect, but after some time a yellow precipitate falls.

5. A bar of zinc throws down a white gelatinous precipitate.

Only ten salts of peroxide of zinc have been hitherto examined, and not one of these has been subjected to an accurate analysis.

Genus 26. Salts of Elach Oxide of Copper.

The greater number of the salts of copper are soluble in water, and the solutions have a blue or green colour, or at least they speedily acquire that colour on exposure to the air. Their taste is exceedingly nauseous, and they are poisonous.

1. When ammonia is poured into a solution of a cupreous salt, the colour becomes a deep blue, with a slight shade of red.

2. Prussiate of potash occasions a red precipitate, which becomes brown when washed and dried.

3. Sulphobydrate of potassium, or sulphuretted hydrogen, throws down a black precipitate.

4. Gallic acid occasions a brown precipitate.

5. A plate of zinc or iron, when put into a solution of a salt of copper, throws down the copper in the metallic state.

The salts of copper which have been formed and examined by chemists amount to seventy-one. Of these, thirty have been subjected to analysis. There are no fewer than eighteen double salts which contain black oxide of copper as a constituent. Thus the salts of black oxide of copper at present known amount to eighty-nine.

Genus 2Ί. Salts of Suboxide of Copper.

Of this genus only nine salts have hitherto been examined. They are never blue or green, but white, red, brown, or black. When exposed to the air they speedily absorb oxygen, and are converted into the corresponding salts of black oxide of copper.

Genus 28. Salts of Oxide of Bismuth.

The salts of bismuth are commonly white. Their solutions in water are transparent and colourless. When much diluted with water, a white precipitate falls, consisting chiefly of hydrated oxide of bismuth.

1. Prussiate of potash occasions a white precipitate, sometimes with a shade of yellow.

2. Sulphohydrate of potassium, or sulphuretted hydrogen, throws down a dark-brown precipitate.

3. Gallic acid, or the infusion of nutgalls, occasions an orange-yellow precipitate.

4. When a plate of copper or tin is put into a solution of a salt of bismuth, the bismuth is precipitated in the metallic state.

The salts of bismuth which have been examined by chemists with more or less accuracy amount to twenty-three, several of which have been subjected to analysis.

Genus 29. Salts of Suboxide of Mercury.

Mercurial salts are very frequently but little soluble in water. Some of them crystallize, and others can be obtained only in the state of white powders.

1. When strongly heated they are volatilized and dissipated, and traces of mercury may sometimes be observed.

2. Prussiate of potash occasions a whitish precipitate, which becomes yellow on exposure to the air. This precipitate is very scanty, unless the solutions be concentrated.

3. Sulphohydrate of potassium occasions a black precipitate. The same precipitate is thrown down by sulphuretted hydrogen.

4. Muriatic acid, when poured into a solution of a salt of suboxide of mercury, occasions a white precipitate.

5. Gallic acid, or the infusion of nutgalls, occasions an orange-yellow precipitate.

6. Hydriodate of zinc dropt into a solution of a salt of suboxide of mercury throws down a fine yellow precipitate.

7. Chromate of potash throws down a fine red precipitate.

8. When potash is dropt into a solution of a salt of suboxide of mercury, a black precipitate falls, not soluble in an excess of the potash.

9. A plate of copper being put into a liquid mercurial salt, gradually precipitates mercury in the metallic state.

The salts of suboxide of mercury hitherto examined by chemists amount to thirty-eight. Of these, ten have been subjected to analysis, but not with much accuracy. There are very few double salts known in which the suboxide of mercury forms a constituent.

Genus 30. Salts of Ped Oxide of Mercury.

The salts belonging to this genus have a considerable analogy to those of the last. When they dissolve in water the solution is transparent and colourless. The salts of this genus insoluble in water dissolve in nitric acid, and the solution is transparent and colourless.

1. When potash is dropt into a salt of red oxide of mercury, a yellow precipitate falls, not soluble in an excess of the potash; but if to the liquid we previously add some sal ammoniac, then the potash precipitate is white. The same colour is observable when the liquid contains much uncombined acid.

2. Ammonia throws down a white precipitate, not soluble in an excess of the re-agent.

3. Carbonate of potash throws down a reddish-brown precipitate, not soluble in an excess of the re-agent. Carbonate of ammonia throws down a white precipitate. The same observation applies to oxalate of ammonia and prussiate of potash. 'The prussiate of potash precipitate after some time becomes blue.

4. Sulphohydrate of ammonia added in very small quantity produces a black precipitate, which, when the liquid is shaken, becomes white, and remains long suspended. When sulphobydrate of ammonia is added in excess, the precipitate is black, and is not altered by agitation. It is insoluble in ammonia, but dissolves in potash. Sulphuretted hydrogen acts in the same way.

5. Iodide of potassium throws down a scarlet-coloured precipitate, and chromate of potash a yellowish-red powder, provided the liquid be not too dilute.

6. A plate of copper put into a solution of oxide of mercury is soon whitened, being converted into an amalgam.

7. When a salt of oxide of mercury is mixed with carbonate of soda, and heated before the blowpipe, the mercury is restored to the metallic state.

The salts of red oxide of mercury hitherto examined by chemists amount to twenty-seven.

Genus 31. Salts of Oxide of Silver.

The only acid which dissolves silver well is the nitric. The solution is transparent and colourless, but very caustic. It readily deposits beautiful crystals. Many of the salts of silver are insoluble in water.

1. The solutions of the soluble salts are colourless and transparent. The insoluble salts are white, and in some cases yellow or red.

2. A solution of potash dropt into a salt of silver gives [7:6:452] a light-brown precipitate. Carbonate of potash throws down a white precipitate. Both of these precipitates are redissolved when ammonia is added.

3. When ammonia, in very small quantities, is poured into a salt of silver, a brown precipitate falls, which dissolves at once when a little more ammonia is added.

4. When the salts of silver are exposed on charcoal to the action of the blowpipe, they are reduced, and a globule of silver is obtained.

5. Prussiate of potash, when dropt into a solution of a salt of silver, occasions a white precipitate.

6. Sulphohydrate of potassium throws down a black precipitate.

7. Muriatic acid, or the chlorides of the alkaline bases, occasion a heavy white flaky precipitate resembling curd.

8. Gallic acid and the infusion of nutgalls occasion a yellowish-brown precipitate, at least in several of the solutions of silver.

9. The solution of sulphate of iron precipitates the silver in the metallic state.

10. When a plate of copper is put into a solution of silver, the silver is precipitated in the metallic state, retaining, however, a little of the copper in the state of an alloy.

The salts of silver hitherto examined by chemists amount to forty-four. Very few of them seem to contain chemically combined water. The number of double salts into which oxide of silver enters as a constituent amount to ten. Thus all the silver salts at present known amount to fifty-four.

Genus 32. Salts of Peroxide of Gold.

The oxide of gold appears to partake more of the properties of an acid than of a base; yet there are a few saline compounds known, in which it is united with an acid as a base. Indeed the only solution of gold which we are acquainted with is the chloride, which is yellow and very acrid. The action of re-agents on this solution is as follows :—

1. Potash added in excess produces no change at first, but by degrees the liquid assumes a greenish colour, and a little black matter falls down.

2. Ammonia throws down a dirty-yellow precipitate, which is fulminating gold, and which is redissolved by adding the ammonia in great excess.

3. Carbonate of potash produces no precipitate, but carbonate of ammonia effervesces with the liquid, and throws down a yellow precipitate.

4. Prussiate of potash strikes an emerald·green colour.

5. Nitrated suboxide of mercury occasions a black precipitate.

6. Sulphate of iron throws down the gold in the metallic state; so does oxalic acid, but not so completely.

7. Protochloride of tin strikes a purple colour with very dilute solutions, and throws down a brown-coloured precipitate when the solution is more concentrated.

8. Sulphohydrate of ammonia throws down a dark-brown precipitate, which is redissolved on adding an excess of the sulphohydrate.

The salts of gold at present known amount only to eight, namely, the sulphate, nitrate, iodate, arseniate, molybdate, acetate, benzoate, and pinate, all of which have been examined very superficially.

Genus 33. Salts of Peroxide of Platinum.

These salts are not better known than those of the preceding genus. Almost the only solution of platinum which we can form is the chloride. Its characters are the following :—

1. It has a fine brownish-red colour, and is transparent.

2. Potash throws down a yellow precipitate, which is not sensibly soluble in acids; but it dissolves when heated in an excess of potash, and does not again precipitate when the liquid cools.

3. With ammonia the phenomena are exactly the same as with potash.

4. Carbonates of ammonia and potash produce a similar effect. But the precipitates are not redissolved when heated in an excess of the alkaline carbonates.

5. Neither soda nor its carbonates throw down any precipitate.

6. Nitrated suboxide of mercury throws down a yellowish-red precipitate.

7. Neither oxalic acid nor phosphate of soda occasions any precipitate.

8. Sulphuretted hydrogen changes the colour to brown, and by degrees a brown precipitate falls, which becomes gradually black. Sulphohydrate of ammonia produces the same effect, but the precipitate is redissolved when an excess of the sulphohydrate is added.

9. A plate of zinc precipitates platinum from its solution in the state of a black metallic powder.

Only eight salts belonging to this genus have been examined, and these very superficially. They are the sulphate, nitrate, iodate, arseniate, chromate, oxalate, benzoate, and camphorate.

Genus 34. Salts of Protoxide of Platinum.

This genus of salts, owing to the difficulties attending the productions of protoxide of platinum, is almost wholly unknown. Only three of them have been formed, namely, the sulphate, nitrate, and acetate. They are soluble in water, and have a greenish-brown colour.

Genus 35. Salts of Oxide of Palladium.

The scarcity of palladium has hitherto prevented chemists from fully investigating these salts.

1. They are almost all soluble in water, and the colour of the solution is a fine red.

2. Prussiate of potash occasions a dirty yellowish-brown precipitate.

3. Sulphohydrate of potassium occasions a blackish-brown precipitate.

4. The alkalies throw down an orange-coloured precipitate.

5. Mercury and sulphate of iron throw down the palladium in the metallic state.

6. Protochloride of tin renders the solution opaque, by throwing down a brown precipitate; but if the solution be sufficiently diluted, it assumes a fine emerald-green colour.

7. Neither nitrate of potash nor sal ammoniac occasions any precipitate.

The salts of palladium hitherto formed amount only to eight, namely, sulphate, disulphate, nitrate, iodate, arse-niate, oxalate, citrate, and benzoate.

Genus 36. Salts of Peroxide of Rhodium.

The characters of the salts belonging to this genus are so imperfectly known that a detailed description is out of our power. The metal is so scarce that chemists have it not in their power to examine them.

1. Their solution in water is red.

2. Prussiate of potash occasions no precipitate.

3. Neither is any precipitate produced by sal ammoniac or the alkaline carbonates; but the pure alkalies throw down a yellow powder, soluble in an excess of alkali.

Only four of these salts are at present known, namely, sulphate, nitrate, arseniate, and acetate.

Genus 37. Salts of Protoxide of Iridium.

This genus of salts is almost entirely unknown.
[7:6:453]

1. The salts of iridium appear to be soluble in water, and to have a colour at first green, but which changes to red by concentrating the solution in an open vessel.

2. Neither prussiate of potash nor the infusion of nutgalls occasions any precipitate, but both render the solution colourless.

3. They are partially precipitated by sal ammoniac, and the precipitate has a deep-red colour.

Genus 38. Salts of Oxide of Osmium.

This genus of salts is still altogether unknown.

Genus 39. Salts of Oxide of Tellurium.

The scarcity of tellurium, which cannot be procured in any quantity, has prevented the investigation of these salts.

1. The salts of tellurium, when insoluble in water, are white powders. The soluble salts form transparent and colourless solutions.

2. Alkalies throw down from the solution a white precipitate, which disappears again if the alkali be added in excess.

3. Prussiate of potash occasions no precipitate.

4. Sulphohydrate of potassium throws down a brown or blackish precipitate.

5. The infusion of nutgalls occasions a flaky precipitate of a yellow colour.

6. Zinc, iron, and antimony, when put into a solution of tellurium in an acid, cause the tellurium to separate in the state of a black powder, which assumes the metallic brilliancy when rubbed.

7. Sulphite of ammonia, when added to a solution of tellurium, throws down a black powder, which is tellurium in the metallic state.

8. Sulphohydrate of ammonia added in excess to a solution of tellurium, throws down a black precipitate, which is redissolved by digestion if the quantity of sulphohydrate be sufficient.

Only nine of these salts have been formed, and not one of them has been subjected to a rigid analysis.

Genus 40. Salts of White Oxide of Arsenic.

It has been already stated in this article, that white oxide of arsenic possesses the characters of an acid, and not of a base. Yet several acids have the property of dissolving this acid, and of keeping it in solution, so that with them it seems to act the part of a base. Sulphuric acid dissolves it by digestion, but lets it fall again on cooling. Muriatic acid forms a permanent solution, from which, however, most of the white oxide falls when the solution is diluted with water.

Genus 4L Salts of Protoxide of Antimony.

The best known solution of antimony is the solution in muriatic acid. It becomes milky when diluted with water, but if an excess of muriatic acid be added, the precipitate is again redissolved.

1. Potash or ammonia added to this solution throws down a white precipitate, which is not redissolved by adding an excess of the alkali.

2. The same effects are produced by carbonate of potash and carbonate of ammonia.

3. Phosphate of soda and oxalic acid also occasion a white precipitate.

4. Prussiate of potash occasions a white precipitate when dropt into a solution of protoxide of antimony. The precipitate is merely the protoxide of antimony. When the precipitate is applied in a sufficiently concentrated state, no precipitate falls.

5. Sulphohydrate of ammonia throws down an orangecoloured precipitate, which is redissolved by adding an excess of the precipitant. Sulphuretted hydrogen throws down the same orange-coloured precipitate.

6. When a plate of iron or zinc is plunged into an antimonial solution, a black powder precipitates in great abundance, and very speedily, when there is an excess of acid and the solution is not too much concentrated.

The salts of protoxide of antimony hitherto examined amount to sixteen. There is also a double salt containing the same oxide, tartar-emetic, which is better known than any other of the antimonial salts. It is a compound of
[table]

Genus 42. Salts of Protoxide of Chromium.

The solutions of the salts of protoxide of chromium (for the greater number of them are soluble in water) have usually a dark-green colour, though some of them are blue and some of them purple. The intensity of the colour is such that most of them are opaque, even when dilute. When evaporated to dryness they do not yield crystals, but leave an opaque mass of so deep a green that it appears black. The taste of these solutions is a powerful and pure sweet, which is very agreeable when the solution is slightly acidulated by a trifling excess of acid.

1. Potash throws down a green precipitate, which is again dissolved by adding an excess of the alkali.

2. Ammonia and its carbonate also throw down a green precipitate.

3. Prussiate of potash occasions no precipitate; but when the mixture is heated it becomes dark brown or opaque, yet no precipitate falls.

4. The infusion of nutgalls throws down a green precipitate in flocks.

5. Sulphuretted hydrogen occasions no precipitate, provided the salt of chromium be free from all traces of chromic acid. Sulphohydrate of ammonia throws down a precipitate in green flocks, probably in consequence of an excess of ammonia.

6. When benzoate of potash is dropped into a concentrated solution of muriate of chromium, a precipitate falls; but no precipitate falls when the solution is dilute.

The salts of chromium hitherto examined amount to eighteen, besides a few double salts into which the protoxide of chromium enters.

Genus 43. Salts of Protoxide of Uranium.

The protoxide of uranium has a dirty-green colour, and its salts, at least when in solution in water, have the same colour. The taste of these salts is astringent.

1. Caustic potash dropt into a solution of protoxide of uranium throws it down green.

2. Prussiate of potash throws down a brownish-red precipitate, which does not assume the form of flakes, like prussiate of copper.

3. Gallic acid strikes a chocolate-brown colour when the salt is neutral.

4. Sulphuretted hydrogen occasions no precipitate, but sulphohydrate of ammonia throws down a brownish-yellow powder.

5. No precipitate is occasioned by zinc, iron, or tin.

The salts of protoxide of uranium are almost unknown; only three of them, the sulphate, nitrate, and carbonate, having been hitherto formed. The carbona'te is a lightgreen powder..
[7:6:454]

Genus 44. Salts of Peroxide of Uranium.

The colour of the salts of the peroxide of uranium is a fine yellow, and their taste is astringent.

1. Gallic acid and prussiate of potash produce the same effect upon them as upon the last genus.

2. Carbonate of ammonia throws down a yellow precipitate, which is redissolved by an excess of the carbonate. The solution has a lemon-yellow colour.

3. Carbonate of soda throws down a yellow precipitate, which is rcdissolved by an exccss of the precipitant.

4. Chromate of potash throws down a fine ochre-yellow precipitate, of great intensity of colour.

5. Phosphate of soda throws down a yellowish-white precipitate.

The salts of peroxide of uranium hitherto examined amount to twenty-five. Of these, seven have been subjected to analysis. From these analyses it appears that this oxide is much given to combine with an atom and a half of acid, and so to form sesquisalts. There are also five double salts known into which the peroxide of uranium enters; so that the salts of peroxide of uranium known amount to thirty.

Genus 45. Salts of Protoxide of Molybdenum.

This genus of salts has been very superficially examined. Most of them have a green, brown, or black colour, similar to the solution of sesquioxide of manganese in cold muriatic acid, without the evolution of chlorine. The taste is simply astringent, without any thing metallic. They are not so apt to absorb oxygen as the salts of deutoxide of molybdenum, and may therefore be concentrated without so much risk of alteration. Sometimes (especially when they have an excess of acid) they assume a purple colour, precisely like the salts of sesquioxide of manganese in the same circumstances. Eleven of these salts have been formed, but they have been all very superficially examined.

Genus 46. Salts of Deutoxide of Molybdenum.

The salts of deutoxide of molybdenum, while they retain water of crystallization, arc red.; but when deprived of their water they become black. Their solutions have an astringent taste, and communicate at the same time an impression of acidity, and leave a feeling of something metallic in the mouth.

1. When infusion of nutgalls is added to a solution of these salts, the colour becomes bright yellow, with a shade of brown, and a small quantity of grayish-brown matter precipitates.

2. Prussiate of potash throws down a dark-brown precipitate, which is not redissolved by an excess of the precipitant.

3. A rod of zinc strikes a black colour, while protoxide of molybdenum mixed with zinc gradually precipitates.

4. The insoluble salts of deutoxide of molybdenum, when put into an alkaline solution, become black, because the oxide is changed into molybdic acid, and is taken up, provided there be a sufficient quantity of alkali.

Thirteen salts of deutoxide of molybdenum have been examined, though rather superficially. The difficulty of procuring the deutoxide in sufficient quantity presents a bar to these investigations.

Genus 47. Salts of Molybdie Acid.

Molybdic acid is not only capable of forming salts by combining with bases, but it may also be made to act the part of a base, and combine with acids.

Molybdic acid does not combine with water; but when molybdenum or its oxides are acidified by nitric acid, this acid dissolves molybdic acid; and when the solution is di luted with water it has a yellow colour; but it soon be-: comes muddy, and deposits molybdic acid in the form of a white powder. When this precipitate is washed and dried it is a white matter, which, when ignited, gives out about one per cent, of water. The ignited mass is soft to the touch, and may be spread upon the skin. In this state it dissolves easily in acids, and forms a genus of salts which have not been much examined. About nine of them have been examined, though rather superficially. They have either a yellow colour, or are colourless and transparent.

Genus 48. Salts of Tungstic Acid.

It is known that tungstic acid is capable of combining as a base with other acids. But none of these salts have been hitherto examined except the sulphate and nitrate, and these superficially. The former is a white, the latter a yellowish powder, both soluble in water.

Genus 49. Salts of Columbic Acid.

The white oxide of columbium, though it possesses the characters of an acid, is capable also of combining with acids as a base, and of forming salts which have scarcely been examined. The only salt of this kind hitherto examined is the sulphate. With phosphoric and boracic acids columbic acid fuses into a transparent and colourless glass.

Genus 50. Salts of Titanic Acid.

The characteristic property of solutions of titanic acid in acids is the bulky, dark reddish-brown precipitate, which falls on the addition of infusion of nutgalls, similar in appearance to coagulated blood.

1. Titanic acid is thrown down from its solution in acids by boiling, but the precipitate cannot be washed. When we collect it on a filter, the liquid passes colourless as long as it is acid; but when it becomes pure water, it assumes a milky appearance, and the whole titanic acid passes along with it through the filter. When the solution contains zirconia, the whole titanic acid cannot be separated by boiling.

2. Titanic acid is not precipitated by sulphuretted hydrogen gas nor by sulphohydrate of ammonia added in excess.

3. When a rod of tin is plunged into a solution of titanium, the liquid around it gradually assumes a fine red colour. A rod of zinc, on the other hand, occasions a deep-blue colour.

The salts of titanic acid hitherto examined by chemists amount only to nine; and of these, not one is capable of crystallizing, and none of them constitutes a neutral salt.

CLASS II.—CHLORINE SALTS.

Chlorine, like oxygen, combines with all the salifiable bases, and doubtless forms acids with many of them; but except those of muriatic acid or hydrochloric acid, scarcely any of the salts of chlorine have been investigated. Of late, indeed, the salts of chloride of mercury, and other eight chlorides which possess acid properties, have been formed and examined by Bonsdorf. But this rich field is still very imperfectly traversed.

Genus 1. Muriates or Chlorides.

The chemical law is, that whatever principle has converted the acidifiable base into an acid, the same principle must have converted the alkalifiable base into an alkali. Oxygen acids unite only with oxygen bases, and chlorine acids with chlorides. When a chlorine acid is united to an oxide, a double decomposition usually takes place, [7:6:455] water being formed and a chloride. Muriates, therefore, must consist of muriatic acid united to a chloride; but such salts, supposing them to exist, have not yet been investigated. Most of the salts usually called muriates are really chlorides. Whether these are also muriates has not yet been determined.

A considerable number of the chlorides are soluble in water. The alkaline chlorides have a saline taste, and form transparent and colourless solutions. Such also are the solutions of the earthy chlorides. The colours of the metalline chlorides depend upon the nature of the metallic base.

When a solution of nitrate of silver is dropt into a chloride, a white, heavy, curdyprecipitatefalls, which dissolves readily in ammonia, and which blackens when exposed to the direct rays of the sun.

The number of chlorides and muriates at present known amount to forty-seven, the greater number of which have been subjected to a rigid chemical analysis.

Genus 2. Chlorostannates.

Both the chlorides of tin possess the characters of an acid, though only a very few of their chlorostannates have been hitherto examined. Chlorostannate and bichloro-stannate of ammonia may be obtained in crystals, by mixing sal ammoniac with a solution of chloride of tin. Chlorostannate of potassium, sodium, and barium, have also been formed. No doubt many other salts belonging to this genus might be obtained, if the requisite trouble were taken.

Gemis 3. Chlorohydrargyrates.

Corrosive sublimate possesses the characters of an acid, and is capable of combining with other chlorides, and of forming a genus of salts, to which the name of chlorohy-drargyrates has been given. Some of these, as sal alern-l>roth, or chlorohydrargyrate of ammonia, have been long known. Eighteen of these salts have been particularly examined by Bonsdorf, and most of them analysed by him. With many of the bases it would appear that corrosive sublimate is capable of combining in various proportions.

Genus 4. Chloro-aurates.

The chloride of gold possesses likewise acid properties, and combines readily with the alkaline chlorides, with several of which it forms beautiful crystals. Several of these salts have been long known, while others have been examined more lately by Professor Bonsdorf. There are eleven chloro-aurates which have been examined, and four of these have been subjected to analysis.

Genus 5. Chloroplatinates.

It has been long known that chloride of platinum unites with sal ammoniac and with several other chlorides. Bonsdorf has lately turned his attention to these salts, and examined fifteen of them. No fewer than eleven of these have been subjected to analysis. They consist chiefly of one atom of bichloride of platinum united to one atom of an alkaline chloride. Water, when present, is either in four, six, or eight atoms; but several of the salts contain no water.

Genus 6. Chloropalladiates.

Chloride of palladium combines with chlorine bases, when, after adding a little muriatic acid, the solutions are mixed together. The mixture must be evaporated to dryness, the residue dissolved in water, and crystallized in the vacuum of an air-pump over sulphuric acid. The chloropalladiates hitherto examined are very soluble in water, and likewise in alcohol. They have usually a brown colour. Ten of them have been examined, chiefly by Bonsdorf.

Gemis r l. Chlororhodiates.

This genus of salts, consisting of chloride of rhodium combined with alkaline chlorides, owing to the great scarcity of rhodium, is very imperfectly understood. Only two of them are known, namely, chlororhodiates of potassium and sodium, both of which have been subjected to analysis.

Genus 8. Chlorο-iridiates.

This genus of salts is equally unknown with the preceding, and for a similar cause, the difficulty of procuring iridium. Five combinations of chloride of iridium with alkaline chlorides have been formed, and examined with more or less care.

Genus 9. Chloro-osmiates.

Five salts composed of chloride of osmium united to an alkaline chloride have been examined by Berzelius, and their properties imperfectly investigated.

CLASS III. BROMINE ACID SALTS.

The analogy between chlorine and bromine is so perfect that we cannot have the least doubt that both are capable of entering into similar combinations. But from the short time that bromine has been known, it is evident that chemists have not yet had time to examine the whole of its combinations. Indeed the only salts of bromine with which we are at present acquainted are the hydrobromates or bromides.

Genus 1. Bromides or IIydrobrornates.

These salts are easily recognised by the property which they have of becoming yellow and giving out bromine when they are acted on by hodics which have a strong affinity for hydrogen, as chloric acid, nitric acid, and especially chlorinc. All the bromides are decomposed by chlorine, with the disengagement of bromine. The bromides or hydrobromates hitherto examined and described amount to twenty-eight.

Genus 2. Eromohydrargyrates.

The bromide of mercury possesses the characters of an acid; and two of the salts which it forms have been noticed by Lowig, namely, bromohydrates of ammonia and of potassium, CLASS IV. IODINE ACID SALTS.

The investigation of this class of salts has not made much greater progress than the preceding. But now that iodine can be procured at a cheap rate, it is to be hoped that some chemist will take the trouble to investigate them., Genus 1. Hydriodates or Iodides.

The analogy of these salts is complete with the chlorides and bromides. They must all be alike in their composition. There are twenty-three iodides at present known.

Genus 2. Iodostannates. Genus 3. Iodoplumbates. Genus 4. Iodohydrargyrates.

It is known that the iodides of tin, lead, and mercury have acid properties, and of course that they are capable [7:6:456] of combining with the alkaline iodides and forming salts; but few or none of these salts have been examined, except four iodohydrargyrates, which were investigated by Bonsdorf.

CLASS V.—FLUORINE ACID SALTS.

As fluorine has not hitherto been obtained in a separate state, it must still be regarded as a hypothetical substance. But the evidence in its favour is so strong, that we believe all chemists are at present disposed to consider it as by far the most probable opinion. At all events, the genera of salts classed under it have a real existence, whatever may be the ultimate end of our views respecting the nature of their constitution.

Genus 1. Fluorides, IIydrofluates, or Eluates.

The salts composed of fluoric or hydrofluoric acid have received different names, according to the opinion entertained respecting the nature of the acid which they contain. Those who consider it as a compound of a combustible base and oxygen call these salts fluates ; those who consider the acid as a compound of fluorine and hydrogen call them hydrofl nates ; while those who are of opinion that fluorine is analogous to oxygen, and that when hydrofluoric acid comes in contact with a base a double decomposition takes place (fluorine uniting with the base, while the oxygen and hydrogen form water), give them the name of fluorides. This last opinion is by far the most plausible, though it would be too much to affirm that it has been demonstrated.

The fluorides or hydrofluates hitherto described and examined by chemists amount to thirty-six: the greater number of these are soluble in water. The fluorides of barium, strontium, calcium, and magnesium, are insoluble. The soluble salts cannot be kept in glass vessels without undergoing decomposition.

Genus 2. Fluoborates.

These salts, consisting of combinations of fluoboric acid and bases, have been but imperfectl; r examined. Twelve of these salts have been formed. They are almost all soluble in water.

Genus 3. Fluosilicates.

Of these salts twenty-seven species have been formed and examined in a cursory manner, almost all by Berzelius. They are mostly soluble in water. Fluosilicic acid affords us an easy method of distinguishing barytes from strontian. It precipitates the former, but forms a very soluble salt with the latter.

There are five other genera of fluorine acid salts, namely, fluomolybdates, fluotung states, fluochromates, fluocolum-bates, and fluotitaniates, which have been so little examined that they may be considered as still almost unknown.

CLASS VI. CYANOGEN ACID SALTS.

This class of salts will ultimately contain a great number of genera. It promises also to throw light upon the nature of organic compounds; for cyanogen is not only itself derived from the animal kingdom, but it is liable to undergo changes quite analogous to those which puzzle us so much at present when we attempt to obtain definite views respecting the organic kingdoms of nature.

Genus 1. Cyanodides and Hydrocyanaies.

That cyanogen, like chlorine, combines with the greater number of simple bases, and converts them into a species of salt, has been proved by the most decisive experiments.

Of these, no fewer than twenty-two have already been formed and described. They are of exceedingly easy decomposition, and constitute the prussiates long ago formed and examined by Scheele. It excited at that time great astonishment that they differed so much from the ferroprussiates.

Genus 2. Cyanates.

As cyanic acid contains oxygen, this genus of salts might with propriety have found its place among the oxygen acid salts. We have placed them here because, in the present state of our knowledge, it is better that all the salts containing cyanogen should be placed together. The cyanates consist of combinations of the cyanic acid with bases. The number of them hitherto formed is only nine, and none of them possesses any remarkable properties.

Genus 3. Cyanurates.

This genus consists of combinations of cyanuric acid with bases. The acid has been so recently discovered, and obtained in so small quantities, that scarcely any of the salts which it forms have been investigated.

Genus 4. Fulminates.

This genus of salts possesses the remarkable property of fulminating in general very loudly when struck upon an anvil, or when heated. They owe this property to the fιιl-minic acid which they contain, the nature and constitution of which has been explained in a preceding part of this article. These fulminates are easily obtained, by double decomposition, from the fulminate of mercury. Mr E. Davy has described no fewer than twenty-four of them. The most formidable of thfem is fulminate of silver, originally discovered by Mr Howard.

Genus 5. Sulphocyanodides.

This genus consists of combinations of the hydrosulphocyanic acid originally discovered by Mr Porrett with bases. It is at present the opinion that this acid loses its atom of hydrogen, while the oxides give out their oxygen, and are converted into simple bases. Hence the name sulphoey∙ anodides by which they are distinguished. Of these salts twenty-seven are known, most of which were first examined by Mr Porrett. The most remarkable of them is the hydrosulphoeyanated peroxide of iron, which has a beautiful crimson colour, and is very deliquescent.

Genus 6. Bisulphocyanodides.

This genus of salts is still almost unknown. Four of them have been formed by Wohler, but only very superficially examined.

Genus Ί. F errocy anodides.

This genus of salts contains those bodies formerly distinguished by the name of ferroprussiates. They are, many of them, powders thrown down by the action of a solution of ferroprussiate of potash on a metallic solution. They consist in general of two cyanodides united together; and it is to this double combination that they are indebted for their greater permanency than the simple cyanodides. The most important of them all is the ferrocyanodide of 1)otassium, which used to be called ferroprussiate, or simply prussiate of potash. It is a fine yellow salt, crystallized in octahedrons composed of two four-sided pyramids with square bases, applied base to base, and the apexes of both pyramids truncated. Its taste is very strong and disagreeable. It loses its water when gently heated. A red heat decomposes the cyanodide of iron which it contains; and by throwing down the iron from its solution, and afterwards evaporating, we obtain cyanodide of potassium.
[7:6:457]

The ferrocyanodides at present known amount to twenty-nine, but the greater number of them have only been very superficially examined.

Many other genera of cyanogen salts will be hereafter added to the preceding list. It is known at present that the following exist :—

Manganese cyanodides. Nickel cyanodides. Cobalt cyanodides. Zinc cyanodides. Copper cyanodides. Mercury cyanodides. Silver cyanodides. Tellurium cyanodides.

All of these, and doubtless many more, are capable of forming each a genus of salts similar to the ferrocyanodides, and doubtless containing as many species.

CLASS VII. SULPHUR ACID SALTS.

It has been already stated that sulphur, when it combines with the acidifiable bases, converts many of them into acids, while its compounds, with the alkalifiable bases, constitute alkalies or salifiable bases. The acid compounds of sulphur we call sulphides, the alkaline sulphureis. A sulphide has the property of combining with a sulpliuret, without decomposition, and of forming a salt; but when it comes in contact with an oxide, chloride, bromide, or iodide, decomposition takes place. Hence all the sulphur-salts contain as a base a sulphuret. The genera of sulphur-salts will increase much when the general attention of chemists is turned towards them. Hitherto only a few have been investigated.

Genus 1. Sulphohydrates.

The acid of this genus has been long known under the name of sulphuretted hydrogen gas, and its acid properties are well determined. But as the term sulphuretted hydrogen is not well adapted for the generic name of a class of salts, it has been deemed requisite to change it to sulphohydrogen, from which sulphohydrate, a term analogous to the generic names of the oxygen acid salts, is easily derived. In a similar way all the genera of the sulphur-salts are formed. What we call sulphohydrates, then, is the same as the salts formerly called hydrosulphurets, and first imperfectly described by Berthollet. Eight of these sulphohydrates have been particularly examined, namely, those which have for their bases ammonia, potassium, sodium, lithium, barium, strontium, calcium, and magnesium.

Genus 2. Eisulphocarbonate.

The acid of this genus is the transparent liquid composed of two atoms of sulphur and one atom of carbon, formerly distinguished by the name of bisulphuret of carbon, and now called bisulphide of carbon. It combines with many of the sulphurets, and forms salts, many of which are insoluble powders; while others are soluble, and capable of crystallizing. Twenty-seven such combinations have been examined, though not with much care. They may be frequently formed by placing bisulphide of carbon in contact with an alcoholic solution of a sulphuret. A good many are easily procured by double decomposition.

Genus 3. Sulpho-arseniates.

Arsenic and sulphur combine, as has been already explained, in three proportions, and all the three possess acid characters. By suĭpho-arseniates we mean those sulphur-salts that have the sulphide of arsenic, composed of
[table]

and whose atomic weight is 9∙75. It is analogous to arsenic acid.

The sulpho-arseniates may be formed in various ways.

1. By digesting a sulphuret with sulphide of arsenic.

2. By treating a sulphohydrate with sulphide of arsenic.

3. When an arseniate is decomposed by sulphide of hydrogen, the oxygen salt is destroyed, and an equal number of atoms of sulphur enter into the salt in place of the oxygen. This decomposition proceeds at first slowly, but becomes at last more rapid; and it is the best method of obtaining in a state of purity those salts that do not crystallize. The decomposition is completed when the salt is no longer rendered muddy by chloride of barium or calcium. Those arseniates which are soluble in muriatic acid (though insoluble in water) may be decomposed, if their basis consists of a metal which is thrown down by sulphide of hydrogen, for example arseniate of copper.

4. When sulphide of arsenic is dissolved in caustic ammonia, or by means of an earthy hydrate: but in that case the sulpho-arseniate is mixed with an arseniate, and the sulphide of arsenic is driven off by acids without any smell of sulphide of hydrogen.

5. When sulphide of arsenic is boiled with the carbonates. The carbonic acid may be completely driven off; but in this case also there is a mixture of arseniate present.

6. When sulphide of arsenic is fused in the dry way with a hydrate or a carbonate, which is present in excess. In that case we obtain a sulpho-arseniate, mixed with a sulphate and an arseniate, while metallic arsenic sublimes.

7. When sulphide of arsenic is digested with a solution of quatersulphuret of potassium. All higher sιιlphurets produce the same salts, while at the same time sulphur is precipitated.

8. When an arseniate is mixed with a sulphohydrate of ammonia. Ammonia and the excess of the sulphohydrate are distilled off, and the sulpho-arseniate remains in the retort. This method answers only with those salts whose bases are not precipitated by ammonia.

The colour of the sulpho-arseniates having an alkaline metal for a base is yellow when anhydrous. The aqueous solutions are nearly colourless. The colour of the metalline salts varies. The taste of these salts is hepatic, and at the same time a very nauseous bitter. When decomposed by an acid, they give out a peculiar hepatic odour, like the smell of orpiment in linseed-oil varnish. Most of them are insoluble in water. Those containing the bases of the alkalies and alkaline earths, and a few others, constitute exceptions. They have a strong tendency to form subsalts, consisting of an atom of the acid combined with an atom and a half of the base. These subsalts crystallize very readily, while this is frequently not the case with the neutral salts; hence the difficulty of obtaining the neutral salts.

When alcohol is mixed with a concentrated solution of these salts, it occasions a peculiar alteration in them. A subsalt containing two thirds of the sulphide of arsenic is precipitated, commonly in a crystalline state, and the liquid becomes yellow. It now holds in solution a bisulpho-arseniate, sometimes mixed with a small portion of the subsalt held in solution. From this spirituous liquid the bisulpho-arseniate may be obtained by hasty evaporation in a flat glass. It leaves a solid matter, of a lemonyellow colour, which is decomposed by water, leaving sulphide of arsenic. If the spirituous solution in considerable quantity be concentrated on the sand-bath it gives, [7:6:458] by slow cooling, a light-yellow striated or sealymass, and at the bottom of the retort is deposited a fine red or reddish-yellow powder. The yellow, crystallized mass is persulphuret of arsenic, and the red substance deposited sulphide of arsenic.

The sulpho-arseniates are decomposed by acids with the evolution of sulphide of hydrogen. If the solution be dilute, no effervescence takes place, the liquid merely smells of sulphide of hydrogen. Even carbonic acid gas passed through the solutions of these salts throws down sulphide of arsenic.

The sulpho-arseniates have a great tendency to form double salts with each other, and this disposition is most remarkable in those which have a tendency to unite when in the state of oxygen salts. Thus sulpho-arseniate of sodium and ammonia unite into a crystallized double salt.

When these salts are heated to redness in an open vessel they are easily decomposed, sulphurous acid and arsenious acid are given out, and a sulphate remains without any trace of an arseniate.

The sulpho-arseniates hitherto examined amount to thirty-seven. Of these, five have been subjected to analysis. For the investigation of these salts we are indebted to Berzelius.

Genus 4. Sulpho-arsenites. '

These salts are composed of orpiment, or sesquisulphide of arsenic, and the alkaline sulphurets. They may be obtained in the samewayas the sulpho-arseniates, substituting for arsenic acid and sulphide of arsenic, arsenious acid and orpiment. They are formed exclusively in the dry way, and cannot be obtained by means of the alkaline sulphurets.

Alkaline sulphohydrates dissolve orpiment only till the solution contains a bisulpho-arseniate. The sulphurets of barium, calcium, and magnesium, take up a very inconsiderable excess of orpiment.

These salts (when their bases are colourless), whether neutral or in the state of subsalts, are colourless, or have only a slight tint of yellow. The salts with coloured bases have in general the same colours with the sulpho-arseniates; their taste and smell are also similar.

They are best obtained either in a solid form or in a dilute solution. The subsalts may be kept better than the neutral or supersalts. When a solution of tìiese salts is evaporated, it begins, at a certain degree of concentration, to assume a brownish-yellow colour. It then deposits a brown powder, which increases till the salt dries, when it is in a great measure decomposed into sulpho-arseniate and subsulpho-arsenite. Water dissolves only the first of these salts, leaving the second, which, however, may be taken up by boiling water. Alcohol produces a similar deposition.

Orpiment dissolves easily in caustic potash or soda. The cold solution is nearly colourless. When boiled it assumes a dark-brown colour, and at last deposits a dark-brown powder, which when dry is almost black.

The sulpho-arsenites with an alkaline basis are not decomposed at a red heat in a retort. The others lose more or less of their orpiment. By alcohol they are decomposed in the same way as the sulpho-arseniates. The subsalts, which are thrown down by alcohol, are obtained only when the solution is not fully saturated with orpiment. By acids they arc altered in a way analogous to the sulpho-arseniates. Easily reducible oxygen bases or oxides form with them, in the cold, arsenites, and when boiled with them, arseniates, while the reduced metal unites with the sulphur, producing a sulpho arseniate.

Thc sólptlons, when exposed to the air, undergo similar alterations with the sulpho-árseniates, but they depo-sľt'ïm síiìjfliur. 1 ' ‘ '· υ ' ; ij ' t; j, , f ∙ t wfi

The sulpho-arsenites described and examined amount to thirty-three. Of these, those which have for a base the sulphurets of the alkalies and alkaline earthy bases are soluble in water. Most of the others are insoluble.

Genus 5. Hyposulpho-arsenites. Realgar, which is a compound of one atom sulphur and one atom arsenic, has likewise the property of combining with alkaline sulphurets. These salts may be called hyposulpho-arsenites, from analogy with the hyposulphites and hypophosphites, which exhibit analogous combinations among the oxygen acid salts.

This combination does not take place directly, for when realgar is digested with sulphuret of potassium, or with caustic potash, it is decomposed, and gives a dark-brown powder, consisting of arsenic combined with a minimum of sulphur. When sulpho-arsenite of potassium is melted with an additional quantity of arsenic, we form hyposulpho-arsenite of potassium, which easily swells up, and the excess of arsenic makes its escape. In water the salt is decomposed, just as when realgar is dissolved in potash.

If orpiment be boiled with carbonate of potash or soda in a tolerably concentrated solution, and be filtered while boiling hot, a colourless liquid passes through, which, after cooling, deposits (within twelve hours) a copious precipitate, quite similar to kermes mineral. This is a hyposulpho-arsenite of potassium or sodium. It is soluble in water, but not so while the liquid contains sulpho-arsenite of potassium in solution. Let it be collected on the filter, and when the liquid has been drained from it, a little pure water must be poured on it once or twice. It soon swells out, becomes gelatinous, and the liquid passes through pure yellow. The salt precipitates again if the liquid holding it in solution be mixed with more water. It dries into a translucent red mass.

On the filter remains a dark-brown powder, insoluble in water, which is a bihyposulpho-arsenite of potassium. It melts easily when heated, gives out nothing volatile, and leaves a translucent red mass, insoluble in water. Caustic potash dissolves it with the same phenomena as realgar. When the neutral sulpho-arsenites of the bases of the alkalies and alkaline earths are exposed to spontaneous evaporation, they leave dark-red insoluble compounds, which are bihyposulpho-arsenites.

With glucinum, yttrium, and aluminum, such compounds are not formed. The red solutions give light-coloured precipitates, with the evolution of sulphide of hydrogen.

With sulphuret of zirconium realgar unites to a darkbrown precipitate, which sinks slowly. With manganese, zinc, and cerium, are obtained red or dark-yellow precipitates, not like the sulpho-arseniates or sulpho-arsenites; but the remaining metals give precipitates quite similar to the sulpho-arsenites.

Genus 6. Sulphomolybdates.

The sulphomolybdates consist of combinations of the alkaline sulphurets with tersulphide of molybdenum, which is analogous in its constitution to molybdic acid. The sulphomolybdates are most easily obtained when an oxygen salt is decomposed by sulphide of hydrogen. The decomposition goes on with difficulty in’ dilute solutions, but rapidly in concentrated ones. The liquid becomes red, like a bichromate, or (if it contain iron) reddish brown. These salts, when pure, have a red colour; a shade of brown indicates the presence of iron. An excess of tersulphide of molybdenum likewise renders the colour darker. During evaporation the liquid emits the smell of sulphide of hydrogen, but no precipitate falls, at least at first.

When burnt they are decomposed. Those which contain the basis of an alkali or alkaline earth are changed [7:6:459] into quatersulphurets of the base, and into bisulphide of molybdenum. The salt of potassium is decomposed to the amount of two thirds, the salt of sodium farther, and the rest altogether. The sulphomolybdates, with weaker bases, give out sulphur, and leave a compound of the base with bisulphide of molybdenum. When the solutions of these salts are left exposed to the air, they are but little altered when in the state of bisulphomolybdates; but the subsalts are oxydized rapidly even in a solid form, and a molybdate with a subsulphite and sulphite is formed, leaving a neutral sulphomolybdate. A grayish-brown matter is gradually deposited, during which the beautiful colour of the solution is altered. It becomes opaque and dark brown, then greenish brown, and at last pure blue. The liquid contains a solution of sulphate and molybdate of potash, together with molybdate of molybdenum.

Thirty-two of these sulphomolybdates have been formed and examined. Several of these crystallize and form very beautiful salts.

Genus 7. Eypersulphomolybdates.

These salts are combinations of the quatersulphide of molybdenum with the sulphurets. Sixteen species have been examined, but not very minutely.

Genus 8. Sulphotungstates.

The acid of these salts is the tersulphide of tungsten, corresponding in its composition with tungstic acid. Thirty-two species have been described by Berzelius, many of them rather imperfectly. Several of them are soluble in water, and form crystals of a ruby-red, or sometimes of a fine-yellow colour. Many of them are insoluble powders, of a yellow or brownish-yellow colour.

Genus 9. Sulphotellurates.

These salts consist of combinations of sulphide of tellurium with the sulphurets. The sulphide of tellurium is best obtained by decomposing either the tellurates or the salts in which oxide of tellurium acts the part of a base, by a current of sulphide of hydrogen. A brown flocky precipitate falls, which is sulphide of tellurium. When heated in close vessels the sulphur is driven off, and pure tellurium remains. Eighteen species have been described, several of which dissolve in water and crystallize. The colour of these salts is usually yellow, sometimes very dark.

Genus 10. Sulpho-antimoniates.

There are three sulphides of antimony, namely, persulphide, analogous to antimonic acid; bisulphide, analogous toantimonious acid; sesquisulphide, analogous to oxide of antimony. Each of these is capable of combining with the sulphurets and forming a genus of sulphur-salts. These may be distinguished by the names of sulpho-antimoniates, sulpho-antimonites, and hyposulpho-antimonites, according to the mode of naming which we adopted for the sulphosalts of arsenic. The antimonial sulphur salts have not yet been investigated; of course it is impossible to give any account of them here. The subject, however, is interesting, and is calculated to throw much light upon some of the most complicated ores in the mineral kingdom. We do not at present know any sulpho-antimoniates; but there are two sulpho-antimonites, namely, feather ore, which was considered as a common ore of sesquisulphide of arsenic, but has been lately shown to be a compound of
[table]

Jamesonite, a mineral first distinguished from common sesquisulphide of antimony by Mohs. It is a compound of
[table]

There are at least five different species of hyposulpho-antimonites whose existence has been recognised in the mineral kingdom. These are,

1. Bertltierite, composed of
[table]

2. Zinhenite, composed of
[table]

3. Bournonite, composed of
[table]

4. Barh-red silver ore, composed of
[table]

5. ⅛Iiarairite, composed of
[table]
PART III.

CHEMISTRY OF ORGANIC BODIES.

The substances which constitute the subjects of the chemistry of organic bodies are the principles of which vegetables and animals are composed. In animals, for example, we find glue, albumen, muscle, bone, &c. In vegetables we have sugar, starch, gum, resin, &c. The object of this part of the article is to give an account of the chemical properties of these most important substances.

Organic bodies differ from unorganized bodies in many important particulars. They are in general of a much more complex character than inorganic bodies, containing a very considerable number of atoms united together in some way that we do not as yet understand completely. It would appear that as many as forty or fifty atoms (and in some cases a great many more), belonging to two, three, or four different simple substances, are somehow or other united so as to constitute an integrant particle of the organic matter.

The electrical theory of affinity, which is at present prevalent in chemistry, necessarily leads to the notion that union can take place only between two atoms in different' states of electricity. The compound atoms or particles thus formed may be conceived to be in opposite states of electricity, though undoubtedly these opposite states must be weaker than in the simple substances before union. One atom combined with one atom makes a binary compound. If two binary compounds be in opposite electrical states they will combine and form a quaternary compound, or a compound containing four atoms. Should these quaternary compounds be in different electrical states, they may combine two and two and make an octonary com[7:6:460]pound, or a compound of eight atoms. Two of these uniting would make a particle containing sixteen atoms. Two of these united would make a particle containing thirty-two atoms. In this way we might suppose compounds to unite, containing, any number of particles whatever, as long as the electric states continued different. But it is evident that the intensity of the electricity must diminish after every new combination; consequently the intimacy of the combination must become less and less, and hence it must happen that they are much more easily decomposed than inorganic bodies, which, containing fewer atoms, or, what comes to the same thing, consisting of a much smaller series of combinations, must be united by a much greater difference in the electric state of the combining bodies.

It is probably the consequence of this little intensity with which the constituents of organic bodies are united, that they are all capable of being decomposed by heat, which is but rarely the case with inorganic bodies. To the same cause probably we are to ascribe the combustibility which almost all of them possess. Even when the constituents of an organic and inorganic body are the very same, we find the organic body combustible, and the inorganic incombustible. Thus oxalic acid and carbonic acid are composed each of carbon and oxygen; oxalic acid of two atoms carbon and three atoms oxygen, and carbonic acid of one atom carbon and two atoms oxygen.

Oxalic acid is combustible, and easily decomposed by heat; while carbonic acid is incombustible, and not decomposed by heat, unless assisted by affinity. Thus, if we pass carbonic acid through red-hot charcoal, it is decomposed and converted into carbonic oxide, which is capable of burning. It is in this way that carbonate of lime is deprived of its acid. The coal with which it is mixed deprives it of an atom of oxygen; and the whole, thus converted into carbonic oxide, occasions, by its combustion, the intense heat which continues for so long a period in a well-constructed lime-kiln. We conceive that most of the peculiarities which distinguish organic bodies are derived from their very complicated structurc, which necessarily involves a feeble affinity. How far their formation and properties depend upon the principle of life, we have no means of determining; but till the inadequacy of the former cause to produce all the peculiarities of organic bodies be proved, we are disposed to rest satisfied with it.

Organic bodies naturally divide themselves into two great branches, according as they belong to the vegetable or animal kingdom. We shall treat of each of these kingdoms in succession.

DIVISION I. OF VEGETABLE BODIES.

Vegetables are too well known to require any definition. They are perhaps the most numerous set of bodies belonging to this globe. The species already known amount to at least 60,000; and as great additions are daily making to this number, and vast tracts of country remain yet unexplored, the probability is, that the whole species of plants on the globe are not fewer than 120,000. The nature of the substances which belong to the vegetable kingdom has attracted the attention of chemists almost from the commencement of the science. Their number has increased as analytical chemistry improved, and very great accessions have been made to that number during the course of the present century.

The principles of vegetables, or the different substances which may be extracted from the vegetable kingdom, naturally divide themselves into three sets, namely, acids, alhalies, and neutral bodies. These three sets will constitute the subject of the three following chapters.

CHAP . I. OF VEGETABLE ACIDS.

The acids which exist in the vegetable kingdom, oı which may be obtained by certain processes from vegetable principles, amount to about fifty-eight. We thoughl it better to describe them in a former part of this article, while treating of primary compounds. We refer the reader who wishes to make himself acquainted with these acids to that part of our article.

CHAP . II. OF VEGETABLE ALKALIES.

Ammonia probably occurs in the vegetable kingdom, but certainly rarely, and rather as a product in certair decompositions which vegetable bodies containing azote are apt to undergo, than as a real constituent of vegetable substances. Potash and soda occur in small quantities ir vegetables, always or almost always in combination with acids. Lime is also a pretty common constituent; but it occurs only in small quantity, and, like potash and soda, is almost always in combination with an acid. Lithia has never been found in the vegetable kingdom; and barytes, strontian, and magnesia, are exceedingly rare. These substances have been described in a preceding part of this article, and are not usually considered as belonging to the vegetable kingdom. But there are a considerable number of vegetable principles, which may be extracted by chemical processes, and obtained in a separate state, and which possess alkaline properties; for they are capable of combining with and neutralizing acids; These in general act with great energy on living beings. Some of them are narcotics; others violent stimulants, and as such very active poisons; while there are others which act as emetics, or cathartics, or tonics. We shall devote this chapter to the description of these important bodies, all of which have been made known to chemists since the beginning of the present century,—with very few exceptions, indeed, since the year 1810. The investigation was begun by Sertürner, an apothecary at Eimbeck, in Hanover, who extracted morphin from opium, and pointed out its alkaline characters in 1817. The subject was taken up by Pelletier and Caventou, who made known a variety of these vegetable alkalies. Of late years Dumas and Boullay, and Liebig, have particularly distinguished themselves in these investigations.

Sect. I.— Of Morphin.

Opium is a milky juice obtained by incisions from the unripe seed vessels of the papaver somniferum. It speedily becomes solid, and assumes the dark-brown colour by which opium is characterized. It has a peculiar smell, and a particular but bitter taste. It has been long used as a narcotic and a powerful antispasmodic. It is a very complicated substance; but the most important of its constituents are two acids and two alkalies. The acids are the meconic and the codeic. The first of these has been described in the former part of this article, but the codeic has never yet been obtained separate, so that its existence is still problematic. The two alkaline bodies have received the names of morphin and narcotin, the latter of which was discovered by Derohne in 1803. Morphin, in opium, is believed by Robinet to~be in combination with codeic acid.

Morphin maybe extracted from opium by the following process; Digest opium in water till every thing soluble is taken up, then evaporate the solution to the state of an extract. Three parts of this extract are agitated with one part and a half of water, and then mixed in a retort with twenty parts of ether, and heated. The retort is attached to a receiver, and boiled till five parts of the ether are distilled off. The ether remaining in the retort has [7:6:461] by this time extracted the narcotin salt from the extract. The process is now interrupted, and the ether in the retort, hot as it is, is decanted into a separate vessel, and the rest of the narcotin salt is washed out of the extract by the five parts of ether that have been distilled over. The thin extract now remaining is allowed to cool, and then mixed with a very little water, and after standing an hour is decanted from a crystalline precipitate, which consists likewise of the narcotin salt. It is now diluted with more water, and then precipitated by caustic ammonia. The precipitate is collected on the filter. When the filtered liquid is heated, a little additional portion of morphin separates, which is added to the former quantity in the filter. After washing it well with cold water, it is dried, and then boiled with alcohol of the specific gravity 0∙84, amounting to three times the weight of the opium employed, and the solution mixed with a little ivory-black, to deprive the morphin of its colouring matter. Being now filtered while boiling hot, the morphin is deposited in white crystals as the liquid cools. By this process the morphin is obtained pure, but the whole portion which exists in the opium is not extracted. Opium yields at an average about one sixteenth of its weight of pure morphin.

. Morphin forms white crystals in prisms, sometimes terminated by four-sided pyramids. When heated cautiously it melts, without undergoing decomposition, into a yellowliquid not unlike melted sulphur, which on cooling becomes white and crystallizes. When heated more strongly in an open vessel it smells like resin, smokes, and burns with a lively red flame, giving out much smoke, and leaving an unburnt charcoal.

Its taste is very bitter and astringent, and when taken into the stomach in a state of solution it acts very powerfully; but in a solid state its action is, comparatively speaking, very trifling. It is insoluble in cold water, and but slightly soluble in boiling water; and the portion dissolved, not exceeding τ ⅜θth of the weight of the water, separates as the solution cools. It dissolves in forty times its weight of cold, and in thirty times its weight of boiling alcohol. It is hardly soluble in ether. It dissolves also in fixed and volatile oils, and may be fused with camphor.

• Morphin has been repeatedly analysed by means of oxide of copper. The most accurate of these analyses seem to be those made by Pelletier and Dumas, and by Liebig. The following little table shows the constituents according to these analyses.
[table]

Liebig made a very careful analysis of sulphate of morphin, and found it composed of
[table]

According to this analysis, the salt is a compound of one atom of acid, one of atom morphin, and six atoms of water; and an atom of morphin weighs 36∙5. But the analysis of the chloride of morphin gave only 34 , 17 for the atomic weight of morphin. The mean of these two quantities is 35∙33. Now the number of atoms of carbon, hydrogen, azote, and oxygen, corresponding with the preced ing analysis, and giving the atomic weight of morphin nearest to 35∙33, is the following·:
[table]

It would appear from this analysis that the atomic weight of morphin is 35∙5, and that it is a compound of no fewer than fifty-nine atoms; but of the way in which these atoms are combined we have at present no distinct idea.

The salts of morphin are formed by dissolving morphin; in the dilute acids till they are saturated, and then evaporating the liquid. They are colourless, and the greater number of them crystallize. They have a very sharp and disagreeably bitter taste. The alkalies precipitate the morphin from the solutions of these salts. But when very dilute solutions of these salts are mixed with caustic ammonia, either no precipitate falls, or it is again taken up; but it appears again when the liquid is heated. They are thrown down by the infusion of nutgalls; and this re-agent is so delicate that it indicates the presence of a morphin salt in solution, containing no more than oõ Ţįth of its weight of it; but as this property is not peculiar to morphin salts, it cannot serve to detect them. The most characteristic property of these salts is, that when they are mixed with a little of a salt of peroxide of iron, they strike a fine blue colour. This colour is destroyed by heat, by alcohol, and acetic ether, but not by sulphuric ether. Sulphate of morphin contains three atoms of water; of these, two atoms may be driven off by heat, but the remaining atom cannot be separated without destroying the salt. Morphin acts most powerfully upon the animal economy when combined with acetic acid. It is the opinion of some that the patent medicine called the black drop, which is known to be more powerful than laudanum, is an infusion of opium in acetic acid.

Sect. II.— Of Narcotm.

The other alkaline constituent of opium, detected originally by Derohne, is narcotin, called opian by some modern German chemists. It may be extracted from opium by means of ether in combination with an acid, hitherto unknown, by the process described in the last section. This salt is to be dissolved in hot water, and digested with some ivory-black, to deprive it of its colouring matter. From the filtered liquid the narcotin is to be precipitated by caustic ammonia. If the precipitate is not colourless, it must be dissolved in muriatic acid, digested again with ivory-black, filtered, and finally precipitated by ammonia.

Narcotin is obtained in white loose flocks, but when it is dissolved in hot alcohol or ether it shoots into rhombic prisms, usually larger than the crystals of morphin. It falls also in scales having a pearly lustre. When the temperature is elevated a little, it melts, and loses about three per cent, of its weight. When cooled very slowly, it crystallizes from a variety of points, but when rapidly cooled it becomes translucent, and splits in all directions. Its behaviour when heated is similar to that of morphin. Cold water does not dissolve it, and hot water not more than 3⅛0th part of its weight of it. Cold alcohol dissolves τ ⅛θth, and hot alcohol ⅛th of its weight of it. Ether dissolves it in considerable quantity, and much more abundantly when hot than when cold. It dissolves likewise in volatile and fixed oils. It is distinguished from morphin [7:6:462] by the following characters: 1. It is tasteless, whereas morphin is bitter; 2. It is soluble in ether, in which morphin is insoluble; 3. Whether in a separate state, or combined with acids, it does not strike the blue colour with solutions of peroxide of iron, which characterizes morphin and its salts.

We have two analyses of it, one by Pelletier and Dumas, and another by Liebig. The following little table shows the results:
[table]

As none of the salts of narcotin have been subjected to analysis, we do not know the weight of an atom of this substance; but the smallest number of atoms of each constituent, corresponding with Liebig’s analysis, is the following:
[table]

This would make the atomic weight as high as 70; but, from the very small quantity of azote present, we think that an error might have easily been committed in that part of the analysis. The analysis of Pelletier and Dumas gives us
[table]

so that the two analyses are irreconcilable. Liebig’s being the latest, and made apparently with much care, is probably the nearest to the truth.

The salts of narcotin are obtained by dissolving that principle in the diluted acid, and then concentrating the solution sufficiently. Their taste is more bitter than that of the morphin salts. They dissolve readily in water, and redden litmus paper. The narcotin is thrown down both by the alkalies and by the infusion of nutgalls. The precipitate by nutgalls has a light-yellow colour. Several of them are soluble in alcohol, and still more soluble in ether.

The action of narcotin is not nearly so violent upon the animal economy as that of morphin. It may be taken to the extent of a couple of drachms in the day, without any sensible effect whatever. Orfila found that half a drachm of it dissolved in oil very soon destroyed the life of a dog. In smaller doses it occasioned a stupor, from which the animal could not be roused. Acetate of narcotin was found almost without action on dogs.

Sect. III.— Of Strychnin.

Strychnin was discovered in 1818 by MM. Pelletier Caventou, in the fruit of three different species of strychnos, namely, nux vomica, ignatia, and columbrvna. The first of these fruits has been long known in this country under the name of nux vomica, the second under that of St Ignatius’ bean, and the wood of the tree which bears the third species of fruit has been long known under the name of snakewood. The upas tree of Borneo, and the woorora, with which the South American Indians poison their arrows, owe their poisonous qualities to the presence of strychnin in them.

Strychnin may be obtained from nux vomica in the following manner: Digest nux vomica, previously reduced to powder, in alcohol, and evaporate the alcoholic solution, which is very deep coloured, to dryness. Dissolve the 1 dry residue in water, and drop into the solution Goulard’s extract as long as a precipitate continues to fall. By this means a variety of substances, particularly the colouring matter of the nux vomica, are thrown down; while the strychnin remains in solution, combined with the acetic acid of the extract (diacetate of lend'). A current of sulphuretted hydrogen is passed through to throw down the lead. To the filtered liquid add magnesia, and boil. The magnesia displaces the strychnin, which is precipitated. Wash the precipitate in cold water, and then digest it in alcohol. The strychnin will be dissolved, while the magnesia (in excess) remains behind. By evaporating the alcoholic solution, the strychnin separates either in powder or in small crystals. The strychnin thus obtained usually contains some brucin, and some other impurities, from which it may be freed by digestion in spirits of the specific gravity 0 ’ 88. The strychnin remains undissolved. It may now be dissolved in boiling alcohol, and left to crystallize.

It crystallizes in very small four-sided prisms; but when the alcoholic solution is rapidly cooled, it falls down in small white grains. It has no smell, but its taste is excessively bitter, leaving a kind of metallic impression in the mouth. It is not altered by exposure to the air. When heated it does not melt, like morphin and narcotin; it gives out no water, but undergoes decomposition when heated to the temperature at which olive oil boils, or about 600°. When strongly heated it swells, blackens, gives out a little empyreumatic oil, some water containing acetate of ammonia, and leaves a very bulky charcoal behind. It requires 2500 times its weight of boiling water, and 6667 times its weight of cold water, to dissolve it. When the cold solution is diluted with a hundred times its weight of water, it still retains a distinctly bitter taste. In alcohol it is exceedingly soluble, even when the spirit is not quite free from water; but it is scarcely soluble in ether. It is soluble in volatile oils, and more soluble when they are hot than when cold. In fixed oils it dissolves only in minute quantity, yet it gives them a bitter taste. When heated with sulphur it undergoes decomposition at the melting point of the sulphur, and sulphuretted hydrogen gas is given out.

Strychnin has been analysed by Pelletier and Dumas, and by Liebig. The following table exhibits the constituents according to their determination:
[table]

Liebig determined the atomic weight of strychnin by the quantity of dry muriatic acid which it is capable of absorbing. A hundred parts of strychnin absorbed 15*02 parts of this gas. This would make the atomic weight 30∙79. The number of atoms which agrees best with the preceding analysis, and with this atomic weight, are the following:
[table]

This would make the atomic weight 30∙5.
[7:6:463]

Strychnin acts with great violence on living beings. About half a grain of it is sufficient to destroy the life of a rabbit: convulsions are induced, and the animal dies in about five minutes, in consequence of a violent attack of tetanus. The same effects take place when strychnin is introduced into a wound. Morphin diminishes the violence of its action, but does not neutralize it or destroy its effects.

Strychnin appears to be one of the strongest of the compound vegetable alkalies, and it precipitates many organic bodies from their solution in acids. The salts of strychnin have an excessively bitter and disagreeable taste. They are precipitated by tannin. When treated with nitric acid they assume a red colour, provided they were in a solid state when the acid was applied. Twelve species of salts of strychnin have been formed and examined. The nitrate and sulphate of strychnin crystallize, and act with more violence when taken internally than strychnin itself. With both nitric and sulphuric acid strychnin combines in two proportions, forming neutral and bisalts. All the salts of strychnin are more poisonous than strychnin itself.

Sect. IV.— Of Prucin.

Brucin was discovered in 1819, by Pelletier and Caventou, in the bark of the Pritcea antidysenterica, usually distinguished by the name of false angustura bark. It exists also in the nux vomica. The easiest method of obtaining it is the following: Macerate the brucea bark in water, mix the infusion with some oxalic acid, and evaporate to the consistence of an extract. Digest this extract at the temperature of 32° with absolute alcohol, which will dissolve every thing except the oxalate of brucin. Boil this oxalate with magnesia and water, and then dissolve the precipitated brucin in boiling alcohol. When the solution cools, brucin is separated in crystals.

. Brucin thus obtained is white, and crystallized in foursided oblique prisms. Its taste is very bitter, with a certain degree of acridity, which remains long in the mouth. When rapidly precipitated, it falls in pearly scales, similar in appearance to boracic acid. The crystals constitute a hydrate of brucin. If they be heated a little above 212°, they melt and give out about 19 per cent, of water. The fused mass has the appearance of wax. When pulverized and put into water, it recovers in a few days its chemically combined water. In the open air it behaves when heated like the preceding bodies. It requires 850 times its weight of cold, and 500 times its weight of boiling water to dissolve it. It dissolves very easily in alcohol, even as weak as 0∙88. It is insoluble in ether and in the fixed oils, but the volatile oils dissolve it in small quantity. Its most characteristic property is the red or yellow colour which it assumes when treated with nitric acid. The protochloride of tin strikes with it a fine violet colour, and the same coloured precipitate falls down. By this mode of precipitation brucin may be separated from morphin when they happen to be mixed.

Brucin has been analysed by Pelletier and Dumas, and by Liebig. The following are the results obtained:
[table]

Todetermine the atomic weight of brucin,“Liebig ascertained how much muriatic acid gas the dry alkali would absorb. The result was, that,eighty-five parts, of brucļn absorb 11∙1 parts of the acid gas. The muriatic acid gas being thrown down by nitrate of silver, he obtained 412 parts of chloride of silver, indicating 10∙15 parts of chlorine. The mean of these two results gives us 35∙64 for the atomic weight of brucin. The number of atoms deduced from Liebig’s analysis, and agreeing best with the atomic weight thus found, is the following:
[table]

This makes the atomic weight 34∙375. Were we to take the number of atoms of carbon at thirty-four, according to the analysis of Pelletier and Dumas, the atomic weight would be 35∙5. This last is probably nearest the truth.

Sect. V.— Of Quinin.

Some steps towards the discovery of this important principle had been made by Vauquelin and by Gomes in 1811; but it was in 1820 that Pelletier and Caventou pointed out its alkaline character, and showed how it might be obtained in a separate state. Since that period sulphate of quinin has been introduced into medicine, and has almost superseded the administration of bark. Quinin may be extracted from the yellow bark, the cinchona cordifolia, by the following process:

Let the yellow bark be coarsely pulverized, and boiled in eight times its weight of water, containing five per cent, of sulphuric acid. Let this boiling be repeated with an additional dose of acidulated water. Filter and squeeze out the liquid portion from the undissolvea bark. Mix the liquid thus obtained with unslaked lime amounting to a fourth of the weight of yellow bark employed. Agitate well, and as soon as it begins to exhibit alkaline characters, let it be passed through the filter. The lime remaining is to be washed with a little cold water, exposed to pressure, and then dried. It is then to be boiled three times in succession in different portions of alcohol of the specific gravity 0∙836. Mix the filtered alcoholic liquors with a little water, and distil. The quinin remains, but not in a state of absolute purity. To free it from the colouring matter with which it is still combined, we must dissolve it in an acid, and digest the solution with ivory·black. When now thrown down by an alkali, it is white. The following method is said to yield pure quinin:

The yellow bark is digested in water holding one per cent, of muriatic acid. The acid liquor is concentrated till it acquires the specific gravity of 1∙109. It is then precipitated by the protochloride of tin, after which the liquid remains only slightly yellow. A current of sulphuretted hydrogen gas is passed through the liquid, to throw down any excess of tin which it may contain. The quinin is now precipitated by means of a caustic alkali.

Quinin crystallizes with great difficulty, but is obtained by precipitation by an alkali in white curdy looking flakes, which, when dried, rarely preserve their white colour. When dissolved in alcohol of 0∙8l5 to full saturation, and left during winter in a dry place to spontaneous evaporation, it shoots into small crystals, the form of which, according to Pelletier, is different from that of cinchonin. Both the crystals and flocks are in the state of hydrate. By gentle heating, about four per cent, of water is driven off, and the quinin melts into a translucent liquid, which when cold assumes the appearance of resin, and, like resin, becomes strongly electrified negatively when rubbed. When the melted matter is put into water it gradually absorbs the chemically combined water.

The taste of quinin is ; excessively bitter, similar to that of the bark from which it has been extracted. It is [7:6:464] slightly soluble in water when assisted by heat, two hundred parts of boiling water being capable of dissolving one part of quinin. It is very soluble in alcohol, which, after evaporation by heat, leaves a soft viscid mass. It dissolves also in ether; and, when assisted by heat, it is soluble in the fixed and volatile oils.

Quinin has been analysed by Pelletier and Caventou, and by Liebig. The following table exhibits the results which they obtained:
[table]

Liebig, to determine the atomic weight of quinin, analysed the sulphate, and found its constituents to be,
[table]

According to this analysis, the atomic weight of quinin is 42∙915. But as the salt is a disulphate, the atomic weight must be 21∙5.

The number of atoms deduced from the analysis of qui-nin by Liebig, and according best with this atomic weight, are as follow:
[table]

This number, 24∙875, considerably exceeds the weight derived from the analysis of the sulphate; yet the ratios of the constituents deduced from Liebig’s analysis have been preserved, excepting a small addition to the oxygen. It is only 1*86 instead of two atoms. We believe that the quantity of azote has been slightly underrated.

The salts of quinin are distinguished by an excessively bitter taste, like that of the bark itself. They are soluble in water, and some of them in alcohol and ether. Their solutions are precipitated by oxalic acid, tartaric acid, and gallic acid, and by the salts containing these acids. They are thrown down also by the infusion of nutgalls. Of these salts, by far the most important is the sulphate, which has been introduced into medicine as a substitute for bark, of which it possesses the medicinal virtues, with this great advantage, that a few grains of it go as far as an ounce of bark. Quinin unites with sulphuric acid in three proportions. The neutral sulphate is deposited by cautious evaporation in long small plates or needles, having a pearly lustre. It is very difficultly soluble in cold water, but dissolves very readily in boiling water. It dissolves easily in alcohol, but is little soluble in ether. When heated it melts, and assumes the appearance of wax. In a higher temperature it assumes a fine red colour, and burns all away without leaving any residue. The water which it contains amounts to 15∙254 per cent, of the weight of the salt. Of this it loses three fourths in a gentle heat. The remainder adheres obstinately to the salt.

Bisulphate of quinin crystallizes in four-sided rectangular prisms. It reddens litmus paper, but its taste is not sensibly sour. At the temperature of 54° it dissolves in eleven times its weight of water. It is very soluble in rectified spirits, but scarcely soluble in absolute alcohol. It effervesces when exposed to the air. The water of crystallization in it amounts to 24∙66 per cent. The composition of these two salts, according to Baup, is as follows:

1. Neutral Salt.
[table]

2. Bisulphate.
[table]

The disulphate of quinin is obtained when a boiling-hot solution of sulphate of quinin is precipitated by disulphate of barytes, added slightly in excess. The solution being filtered while boiling hot and left to cool, deposits the disalt in crystals, which may be purified by washing them in cold water. Few of the remaining salts of quinin crystallize, and none of them has been applied to any useful purpose.

Sect. VI.— Of Cinchonin.

Cinchonin is obtained from the gray or pale Peruvian bark by the same process as quinin, only it is more easily obtained pure, in consequence of the property which it has of crystallizing. Precipitate a solution of it in sulphuric acid by a caustic alkali. Wash the precipitate well, dry it, and then dissolve it in boiling alcohol. When the solution cools, the cinchonin is deposited in crystals.

The crystals are small four-sided prisms. Its taste is similar to that of quinin; at first it seems slight, but it becomes very strong, and remains long in the mouth. When heated it loses no weight, and does not melt until it begins to undergo decomposition, at which temperature a portion sublimes unaltered. It is almost insoluble in cold water, and it requires 2500 times its weight of boiling water to take it up. It is much less soluble in alcohol than quinin, and is almost insoluble in ether. In fixed and volatile oils it dissolves in very small quantity.

The following table exhibits the constituents of cinchonin, according to the analysis of Pelletier and Caventou, and Liebig:
[table]

To determine the atomic weight of cinchonin, Liebig tried how much muriatic acid gas a given weight of cin-chonin would absorb. The result was, that a hundred parts of cinchonin absorbed 22∙698 of the acid. This makes the atomic weight 20-37.

The number of atoms agreeing best with this atomic weight, and derived from Liebig’s analysis of cinchonin, is the following:
[table]

If there were one additional atom of oxygen present, the atomic weight deduced from these numbers would almost tally with that from the muriate.

The salts of cinchonin have a very bitter taste, not un∙i like those of quinin. They exist both neutral and with an excess of acid. Like salts of quinin, they are precipitated [7:6:465] by oxalic acid, tartaric acid, and gallic acid salts, and by the infusion of nutgalls. The sulphate has been tried as a medicine, but it does not answer nearly so well as the sulphate of quinin.

Sect. VII.— Of Veratrin.

Veratrin was discovered in 1819, by Pelletier and Ca-ventou, in the seeds of the veratrum sabadilla, veratrum alburn, and the roots of the colchicum autumnale, or meadow saffron. To obtain it from the seeds of the veratrum sabadilla, the following process may be employed: Boil the seeds in water, and mix the filtered solution with acetate of lead, which throws down the colouring matter. Filter and precipitate the excess of lead by a current of sulphuretted hydrogen. Drive off the excess of sulphuretted hydrogen by heat. Then boil the liquid with magnesia, which throws down the veratrin. Dissolve the veratrin thus thrown down, by digesting the undissolved magnesia in boiling alcohol. From the alcohol it is thrown down by evaporation, or dilution with water. Veratrin, when obtained in this way, is usually yellow coloured. It may be deprived of its colouring matter, either by repeated solutions, or by digesting it with ivoryblack.

>. It is a white powder, which does not seem capable of being obtained in crystals. It has no smell, but when introduced into the nostrils in very minute quantity it produces violent and long-continued sneezing. Its taste is exceedingly acrid, without any mixture of bitterness. When given internally in very minute quantities, it produces excessive vomitings, and irritates the mucous membranes. This irritation proceeds along the intestines when the dose is a little stronger, and a very few grains are sufficient to occasion death.

It is very little soluble in cold water. Boiling water dissolves a hundredth of its weight of it, and acquires a sensible acridity. It dissolves in great abundance in alcohol. Ether dissolves it also, but not in such quantity. It melts when heated to the temperature of about 122°. In this state it resembles wax. On cooling it congeals into an amber-coloured and translucent mass. When strongly heated it swells up, and is decomposed, producing a great deal of oil, water, &c. and leaves a bulky charcoal, which, when incinerated, leaves scarcely any residue. It restores the blue colour of litmus paper reddened by acids.

It was analysed by Pelletier and Dumas, and found by them composed of
[table]

The atomic weight, if any confidence can be put in the analysis of sulphate of veratrin by Pelletier and Caventou, is not less than 150; but their analysis of muriate of veratrin gives only 107 for the atomic weight. The number of atoms which agrees best with the preceding analysis, and with this last atomic weight, is the following:
[table]

This would make the atomic weight 104∙375. It would not be surprising if it should ultimately turn out to be 52, and to be a compound of
[table]

This is nearly in the ratio of the anal; r sis of veratrin by Pelletier and Dumas; and it supposes the sulphate to be a compound of three atoms veratrin and one atom sulphuric acid.

The salts of veratrin have a sharp and burning taste. Veratrin dissolves in concentrated solutions of acids to saturation, and the solutions do not redden litmus paper; but when they are diluted with water they lose their neutral state, a portion of the veratrin separating. These salts cannot be crystallized; when evaporated they assume the form of gummy-like masses. The only one in which traces of crystallization have been observed is the supersul-phate of veratrin; but it must be acknowledged that these salts have been only superficially examined.

Sect. VIII.— Of Emetin.

This substance was discovered in 1817, by Pelletier and Majendie, in the root of the plant used as an emetic, and generally known by the name of ipecacuanha. It may be extracted in the following manner:

The root, previously reduced to powder, is digested in the first place in ether, which separates an oily matter having a strong smell. It is then boiled in alcohol. The alcoholic solution is filtered, mixed with a little water, and the alcohol is distilled off. The residue being mixed with a little more water, is filtered from a fatty matter, which separates. This liquid is now boiled with caustic magnesia, which precipitates the emctin. The undissolved magnesia mixed with the emetin is washed with cold water, and then digested in boiling alcohol, which dissolves the emetin. By evaporating the alcohol, the emetin is precipitated, still mixed with a little colouring matter. To purify it, let it be dissolved in an acid, and mixed and agitated with ivory-black. The liquid being now filtered and precipitated by an alkali, the emetin is obtained in a state of purity.

Emetin thus obtained is in white scales, which become yellowish by exposure to the air. It has a very slight bitter taste, and no smell. It is scarcely soluble in cold water, but boiling water is a better solvent of it. When heated it melts very easily, and sublimes in a temperature hardly so high as 122°. It dissolves very readily in alcohol, but is almost insoluble in ether and oils. It combines with acids like an alkali, though the salts which it forms always redden vegetable blues. It acts very powerfully as an emetic: half a grain taken into the stomach occasions violent vomiting, followed by sleep, and the animal awakes in a state of health. Twelve, or even six grains, occasioned vomiting, followed by death. A violent inflammation of the lungs and intestinal canal appears to be the proximate cause of the death which in this case ensues.

Emetin has been analysed by Pelletier and Dumas, who found its constituents,
[table]

As no attempt has been hitherto made to determine the atomic weight of emetin, this analysis does not enable us to give the atomic constitution of this remarkable substance[7:6:466]; but the smallest number of atoms which correspond with the preceding numbers are the following:
[table]

Hence the atomic weight is 40∙125, or some multiple of that quantity.

Dilute sulphuric acid produces no other effect upon it than to combine with it; but when heated with concentrated acid it is charred and destroyed. Nitric acid dissolves it, and forms a fine red-coloured solution, which gradually passes into yellow, while nitrous gas exhales, and crystals of oxalic acid are formed. Muriatic, phosphoric, and acetic acids combine with it readily, and may be saturated with it. Gallic acid throws it down in the state of a dirty-white precipitate. It is precipitated equally by the infusion of nutgalls.

Sect. IX.— Of Delphinin.

This alkaline body was discovered in 1819, by Lassaigne and Feneulle, in the seeds of the delphinium staphisagria, or stavesaere, which is occasionally employed externally to destroy vermin. It may be obtained in the following manner:

Digest the seeds in water acidulated with sulphuric acid. Then precipitate the acid liquid by an alkali or magnesia. Wash and dry the precipitate, and boil it in alcohol, which dissolves the delphinin. To free it completely from foreign matter, it may be obtained from the alcohol by evaporation, and dissolved in an acid. Let the solution be digested with ivory-black, and after filtration let it be mixed with an excess of caustic ammonia. The precipitate is gelatinous, not unlike newly precipitated alumina. If we dissolve it in alcohol, and evaporate the solution, it falls in the state of a crystalline powder, which when dried becomes translucent.

Its taste is fecbly bitter, and it restores the blue colour of litmus paper reddened by acids. When heated it melts like wax, and on cooling assumes the appearance of resin. It appears, from the experiments of Brandes, to be insoluble in water, though it communicates its taste to that liquid; but it dissolves very easily in alcohol and ether. When these liquids at a boiling heat are saturated with delphinin, it falls down again in flocks as they cool. It is soluble both in fixed and volatile oils.

With acids it forms salts which rarely afford crystals; their taste is bitter and sharp. According to Feneulle, it forms both neutral salts, bisalts, and disalts. Neutral sulphate of delphinin, according to him, is composed of, sulphuric acid 3∙116 or 5, delphinin 100 or 160.

If any confidence could be put in this analysis, the atomic weight of delphinin would be 160. No attempt has hitherto been made to analyse it.

Sect. X.— Of Solanin.

This alkaline substance was discovered in 1822, by Desfosses, in the berries of the solanum nigrum. It has been since discovered in the stalks, leaves, and berries, of the solanum dulcamara, and likewise of the tuberosum., or common potato. To obtain it, we have only to press out the sap of the ripe berries, filter it, and mix it with caustic ammonia. From the unripe berries it may be obtained also, but it is then impure, and of a green colour. The gray precipitate from the ripe berries is to be well washed and dried, and then dissolved in boiling alcohol. By slow evaporation the solanin is deposited in a white powder, having somewhat of a pearly lustre. It has a weakly bitter and nauseous taste. It melts when heated a little above 212°, and on cooling concentrates into a lemon-yellow mass. It restores the blue colour of litmus paper reddened by an acid. It is insoluble in cold water, and requires 8000 times its weight of boiling water to dissolve it. It is very soluble in alcohol, but little so in ether. In the oils it is insoluble. With acids it forms neutral salts which have a bitter taste. The sulphate, nitrate, and muriate, when dry, have a gummy-like appearance, and are easily reduced to powder. According to Desfosses, 100 parts of solanin neutralize 10∙981 parts of sulphuric acid. This would make its atomic weight 45∙5.

From trials made upon a cat, it would appear that solanin is highly emetic and narcotic. Upon dogs it acted as an emetic, but did not induce sleep. In large doses it is poisonous. No attempt has been made to analyse it.

Sect. XI.— Of Picrotoxin.

This alkaline substance was discovered by Boullay in 1811, in the cocculus indicus, which is the fruit of the menispermum cocculus. It may be obtained in the following manner:

Let the berries be boiled in water as long as any thing is taken up, and let the liquid be concentrated into an extract. Digest this extract in alcohol of the specific gravity 0 ι 827. Filter the alcoholic solution, and leave it for some days in a cool place: drops of a solid crystalline fatty matter are gradually deposited on the sides of the vessel. Decant off the clear liquid, and distil it in a retort till the alcohol is abstracted. To the extract remaining in the retort add a little water. Mix it well with about one sixth of its weight of caustic magnesia, and thefi dry the mixture. The extract contains much uncombined acid, and more of the fatty matter formerly mentioned, which now combines with the magnesia and becomes insoluble. Let the matter be now boiled with alcohol of the specific gravity 0∙87, as long as anything dissolves. Mix this liquid with ivory-black, which will deprive it of most of its colouring matter. Filter and evaporate; picrotoxin not quite pure separates during the evaporation. Being again dissolved in spirits, and left to spontaneous crystallization, i t shoots into groups of small, colourless, oblique, four-sided prisms.

Its taste is insupportably bitter. Cold water dissolves] one seventy-fifth, and boiling water one twenty-fifth part of its weight of it. It is still more soluble in water containing a little alkali. Boiling alcohol of 0 , 8 dissolves one third of its weight of it. Ether of 0∙716 specific gravity dissolves four tenths of its weight of it, but it is insoluble both in fixed and volatile oils.

It dissolves in acids, but the saturated solutions still possess acid qualities. Several of its salts are capable of crystallizing. They have a very bitter taste, and are but little soluble. According to Boullay, 100 parts of picrotoxin saturate 11∙1 parts of sulphuric acid. This would make its atomic weight 45.

Sulphate of picrotoxin forms silky needles possessed of great beauty. It is soluble in 120 times its weight of boiling water. The nitrate at first contains an excess of acid. When evaporated to one half, it becomes viscid, and concretes on cooling into a transparent mass, like mucilage. If it be kept in the temperature of 140° it swells up, becomes opaque, and at last quite white, similar in appearance to calcined alum. If in this state we keep it in a temperature below that of boiling water, adding a little water occasionally, the whole excess of acid exhales, and the taste of the salt becomes purely bitter. The phosphate, oxalate, tartrate, and acetate, may be obtained in needles.

Picrotoxin is very poisonous, producing vertigo, convulsions[7:6:467], and death. Ten grains destroyed a dog in about three quarters of an hour. Its salts seem to be less poisonous than the alkali itself. No attempt has hitherto been made to analyse it.

Sect. XII.— Of Daphnin.

This alkaline principle was first detected by Vauquelin in 1812, in the daphne alba. In 1822 it was discovered in the bark of the daphne mezereum by MM. C. G. Gmelin and Baer.

If an infusion of the bark of daphne mezereum be made in boiling water, and if the filtered solution be mixed with magnesia, and distilled in a retort as completely as can be done without burning, we obtain a sharp-tasted liquid, acting strongly as an alkali, and having the smell and taste of the bark. If this matter be saturated with an acid, and the solution concentrated, a crystalline salt is obtained. If we dissolve this salt in a little water, mix the solution with magnesia, and distil, we obtain the alkaline substance in a concentrated state. To this substance the name of daphnin has been given.

. It crystallizes in four-sided oblique prisms, which are transparent and colourless. Its taste is bitter and disagreeable. When heated it melts, swells up, becomes black, and gives out an acid liquid. By nitric acid it is destroyed, and partly converted into oxalic acid. It is but little soluble in cold, but very soluble in hot water. When mixed with a little potash, carbonate of potash, bąrytes water, or lime water, it becomes golden yellow, and loses its property of crystallizing. It is easily soluble in alcohol and ether.

No attempt has been made tα analyse this substance, or to examine the salts which it may form with acids.

Sect. XIII.— Of Digitalin.

Le Royer discovered, in 1824, that if the dried leaves of digitalis purpurea, or fox-glove, be digested with ether in a close vessel, and the solution be afterwards concentrated, by distilling off the ether to the consistency of an extract, water dissolves from this extract an acid salt, having a peculiar alkaline basis, and leaves a green faecula. The acid salt is treated with oxide of lead evaporated to dryness, and the dry residue treated with ether, which leaves the salt of lead, but dissolves the digitalin. When the ether is driven off, the digitalin remains in the form of a brown butter-looking substance, having a sharp taste, and acting weakly as an alkali upon litmus paper reddened by an acid. When dissolved in alcohol, and dried on a glass plate, it gives microscopic crystals, which speedily absorb moisture from the atmosphere. It dissolves readily in water, and possesses the characters to which digitalis is indebted for its celebrity as a medicine. It has been but very imperfectly examined.

Sect. XIV.— Of Jalappin.

This alkaline substance was first obtained by Mr Hume in 1824, by the following process: Jalap in powder is macerated for a couple of weeks in weak acetic acid. A dark-coloured solution is obtained, which is filtered, mixed with caustic ammonia, and well agitated. A granular powder precipitates, consisting, of small crystalline grains, which is to be washed in cold water. Being again dissolved in acetic acid, and thrown down by ammonia, it is obtained in small needles. It has neither taste nor smell. It is insoluble in cold, and but little soluble in boiling water. It dissolves well in alcohol, but is insoluble in ether. Its colour is snow-white. An ounce of jalap yields about five grains of this substance. How far jalappin possesses,the peculiar properties which characterize jalap, has not been ascertained. Indeed the subject has been very imperfectly investigated.

Sect. XV.— Of Parillin and Smilacin.

Palotta stated, in 1825, that if the infusion of sarsaparilla be digested with a little hydrate of lime, an alkaline basis is separated, which, after being washed and dried, is soluble, and, dissolved in boiling alcohol, is deposited as the solution cools, in the state of a white powder, having a bitter and disagreeable taste. It gives a brown colour to tincture of turmeric, dissolves in acids, and forms salts, which produce nausea when taken into the stomach, and diminish the celerity of the pulse. To this alkaline substance he has given the name of parillin.

Falchi states, that if the pith of sarsaparilla be macerated in water, and the solution, after having been treated with ivory-black and filtered, be left to spontaneous evaporation, small light-yellow crystals separate, which are slightly soluble in alcohol, have little taste, yet leave a strong impression in the throat, and give a green colour to syrup of violets. To this substance he has given the name of smilacin. Its properties have scarcely been investigated.

Sect. XVI.— Of Ehabarharin.

Mr Carpenter, in 1826, published the following formula for obtaining this substance: Boil for half an hour six pounds of coarsely bruised Chinese rhubarb, in six gallons of water acidulated with two and a half fluid ounces of sulphuric acid. Strain the decoction, and submit the residue to a second ebullition in a similar quantity of acidulated water, and submit it again to a third boiling. Unite all the three decoctions, and add by small portions recently powdered lime, constantly stirring it to facilitate its action on the acid decoction. When the decoction has , become slightly alkaline, it deposits a red, flocculent precipitate, which is to be separated by straining through a linen cloth. It is to be washed and dried, and digested in alcohol for several hours in the water bath. The rhabarbarin is taken up, while the gypsum, &c. remains. Separate the alcoholic solution, and distil off three fourths of the alcohol. There remains a strong solution of rhabarbarin. Add as much sulphuric acid as will exactly neutralize it, and evaporate the solution to dryness in a low heat. A brownish-red coloured matter is obtained, intermingled with brilliant specks, having a pungent styptic taste, soluble in water, and having the smell of native rhubarb. This sulphate of rhabarbarin contains the whole virtues of rhubarb in a concentrated state.

Sect. XVII.— Of Cathartin.

The examination of the leaves of senna (cassia acutifolia) was begun by Bouillon, La Grange, and more lately by Braconnot; but it was Lassaigne and Feneulle who in 1821 first extracted from it the cathartic principle to which that plant owes its introduction into medicine. To this principle they gave the name of cathartin. It was obtained by the following process: The decoction of the dried leaves of senna was precipitated by acetate of lead, and the filtered solution was treated with sulphuretted hydrogen gas, to throw down all excess of lead that might have been added. The liquid was now evaporated to dryness, and the residue treated with alcohol, which dissolved the cathartin, together with some acetate of potash. The alcoholic solution was distilled off to the consistence of an extract, and then mixed with alcohol containing some sulphuric acid, in order to throw down the potash in the state of sulphate. The liquid was now filtered, to-separate the sulphate of potash. The'excess of sulphuric acid was thrown down by aċetate of lead;'and the excess of lead [7:6:468] being got rid of by sulphuretted hydrogen, nothing remained but cathartin, held in solution by acetic acid. Adding a little ammonia, and evaporating to dryness, we obtain the cathartin in a separate state.

. It has a yellowish-red colour, and cannot be made to assume a crystalline form. Its smell is peculiar. Its taste is bitter and nauseous. It is very soluble both in water and alcohol, but insoluble in ether. When exposed to the open air, it gradually attracts humidity. Its aqueous solution is precipitated in brown flocks by the infusion of nutgalls; and the diacetate of lead occasions a precipitate having the same shade of colour. The sulphated peroxide of iron strikes with it a brown colour. The alkalies do not throw it down from its aqueous solution. Whether it possess alkaline properties has not been examined, but it is probable that it does, because in senna it seems to exist in the state of malate. It possesses the pure gative qualities of senna in great perfection.

Sect. XVIII.— Of Nicoin.

The peculiar principle in the leaves of the tobacco (m- cotiana latifolia and tabacumf to which the name of nico- ŵî-has been given, was discovered by Vauquelin in 1809. Its alkaline properties were afterwards investigated by Posselt and Reiman in 1828. It may be obtained by the following process:

Distil a mixture of dry tobacco with water and hydrate of potash. Pour on the residue twice its weight of water, and distil again. Neutralize the distilled liquid (containing nicoin and carbonate of ammonia) with sulphuric acid, and evaporate in a moderate heat not quite to dryness. Digest the residue with absolute alcohol, which will leave sulphate of ammonia undissolved. To the alcohol solution add a little water, and then distil off the alcohol. Mix the residue with an excess of potash ley, and distil. An oily, almost colourless liquid comes over, which is to be agitated with ether, renewed repeatedly till the whole nicoin is separated from the water. By exposing the ethereal solution to the heat of a water bath, the ether may be distilled off, and the nicoin remains,

Nicoin thus obtained is a colourless liquid, which does not congeal at 21°. Its specific gravity is greater than that of water. It stains paper like grease, and in twelve hours the spots assume a yellowish colour. At 295° it may be distilled slowly over. It boils at 464°. It has a strong smell, especially when heated similar to that of tobacco. It is a strong poison, and acts as a narcotic. A single drop introduced into the mouth of a dog occasioned death.

It dissolves readily in water, alcohol, and ether. This last liquid is capable of separating it from water. It is soluble in fixed and volatile oils. It combines readily with the acids and forms salts. These salts are soluble in water, and the solutions may be evaporated to dryness in a moderate heat without the loss of any nicoin. When mixed with a fixed alkali, the smell of nicoin becomes sensible. When mixed with iodine they strike a kermes red colour. This is characteristic of these salts. The phosphate, sulphate, oxalate, tartrate, and acetate of nicoin have been formed and examined. They all dissolve in water. The phosphate, oxalate, and tartrate crystallize; the sulphate and acetate can be obtained only in the state of a syrup. There is some reason for suspecting that the atomic weight of nicoin is a little below 28*68.

Sect. XIX.— Of Gentianin.

This vegetable principle was discovered by Henry and Caventou i:« 1822, in the root of the Gentiana lutea. It may be obtained by the following process:

The powdered root is digested in ether for twenty-four hours. The yellow-coloured solution, containing gentianin, oil, acid, and an odorous matter, is left to spontaneous evaporation in the open air, by which the gentianin speedily separates. The residue is again digested in alcohol, and the yellow tincture evaporated. The residual matter is again washed with very dilute alcohol, which takes up the gentianin, and leaves an oily matter behind. This last solution being evaporated, there remains behind gentianin, acid, and odorous matter. .When this mixture is boiled with some magnesia and water, and the liquid is evaporated to dryness, the odorous principle is driven off. Ether being boiled in the residue, dissolves pure gentianin, and lets it fall when distilled off.

Gentianin thus obtained is in yellow needles, destitute of smell, but has an aromatic and bitter taste. It is not poisonous, and does not restore the blue colour of litmus paper reddened by an acid. It dissolves slightly in cold water, but sufficiently to communicate its bitter colour to that liquid. Boiling water dissolves it rather more abundantly. It is very soluble in alcohol and ether, and is deposited in crystals when these solutions are evaporated. It combines with the mineral acids, and forms compounds which are slightly coloured, and have a more bitter taste than gentianin itself. The sulphate and phosphate of gentianin are almost colourless. The acetate has a yellow colour. The fixed alkalies deepen the colour of gentianin, and render it rather more soluble in water.

Sect. XX.— Of Corydalin.

This vegetable principle was discovered by Wackenro-der in the roots of the corydalis tuberosa {fumaria bulbο-sa). The coarsely powdered root is macerated for some days in pure water, and the maceration is repeated with water acidulated with sulphuric acid. The filtrated liquids are mixed with carbonate of soda till the liquid becomes distinctly alkaline. The precipitate formed is collected on a filter and washed with alcohol. After being dried it is now to be dissolved in dilute sulphuric acid, and the solution is to be filtered in order to separate a greenish resinous matter which remains undissolved. The acid solution being mixed with some potash, dark-coloured corydalin is precipitated, and after this an additional dose of alkali throws down corydalin in a purer state. If it be dissolved in alcohol, and the solution evaporated, the corydalin may be obtained in crystals.

When pure, it is in the state of white prisms and scales. When heated, it melts below 212°, and floats in a melted state on the surface of water. It has no smell. Its taste is bitter, but not strong. When in solution, the taste resembles that of quinin. On vegetable blues it acts as an alkali.

It is very sparingly soluble in cold water; even boiling water dissolves but a minute quantity of it. It is very soluble in absolute alcohol, but the solubility is diminished the more the alcohol is diluted with water. The solution has a greenish-yellow colour. It dissolves also in ether, and with a similar colour. It dissolves and neutralizes acids. From these solutions it is thrown down white by alkalies, and yellowish white by tincture of nutgalls. The sulphate, muriate, nitrate, and acetate of corydalin have been formed and examined. The last of these salts may be obtained in the state of crystals, but this is not the case with the three others.

Sect. XXI.— Of Xanthopicrin.

This alkaline substance has been lately discovered by Chevalier and Pellelan, in the bark of the Xanthoxylon cariboeum. The bark is digested in alcohol, and the spirit being distilled off, leaves an extract, which is digested first in water, and afterwards in ether. What remains undissolved[7:6:469] is taken up by alcohol; and the solution being evaporated, crystals of xanthopicrin are separated.

It has a greenish-yellow colour and a silky lustre. It has no smell, but a very bitter and astringent taste. It is not altered by exposure to the air, and does not restore the blue colour of litmus paper reddened by an acid. It is moderately soluble in water. It dissolves also readily in alcohol, especially when hot. In cther it is insoluble. It dissolves in dilute acids, and is precipitated by alkalies.

Sect. XXII.— Of Hesperidin.

This substance was discovered by Lcbreton in 1828, in the ripe and unripe fruits of different species of orange and lemon trees. To obtain it, the white portion of the unripe orange is freed by a silver knife from the green rind and the innermost part of the fruit. It is then digested in water of a temperature between 75° and 86°, filtered and concentrated to three fourths of its original bulk. A little albumen precipitates, which must be separated. The malic acid which it contains must now be saturated with lime, and the liquid must be evaporated to the consistency of a syrup. This syrup being digested in alcohol of the specific gravity 0∙817, gum, albumen, a brown bitter matter, and malate of lime, are left undissolved. Let the solution be filtered and evaporated, and let the granular extract remaining be mixed with twenty times its weight of water or distilled vinegar, and often agitated. Being left undisturbed for eight days, the hesperidin is deposited in small crystals.

It has the form of soft, silky needles, without smell, and at first appearing tasteless, but leaving a bitter impression in the mouth. It is almost insoluble in cold water, but it dissolves in sixty times its weight of boiling water. When the solution cools most of it is deposited in white flocks. In cold alcohol it is very little soluble, but it dissolves abundantly in hot alcohol. In ether, fixed and volatile oils, it is insoluble. It is insoluble in dilute sulphuric and muriatic acids, but dissolves in alkaline leys. When the aqueous solution is mixed with sulphated peroxide of iron, a brownish-red precipitate falls. It is very soluble in hot acetic acid.

Sect. XXIII.— Of Guaranin.

This substance was discovered by Martius, in guarana i which is prepared by drying the fruit of the poullinia sorbilis. It may be obtained by the following process: Mix guarana with three tenths of its weight of caleined lime, and digest it repeatedly in alcohol of 0∙852 specific gravity. Filter the solution, concentrate it a little, and allow it to cool in order to separate a greenish fat oil. Evaporate to dryness, and heat the dry residue. Guaranin sublimes, first in the state of yellowish white, and then of white feathery crystals. When heated it gives out a peculiar smell. It has a bitter taste, and possesses the characters of a weak alkali. It is but little soluble in water, but is easily soluble in hot alcohol. It may be fused with camphor into a white crystalline mass. The aqueous solution gives a white precipitate with tincture of nutgalls. When distilled, besides other products, ammonia is given out, showing that it contains azote as a constituent. With iodine it combines into a brown mass. When heated with concentrated sulphuric acid it is partly charred.

Sect. XXIV.— Of Piperin.

This substance exists in black and long pepper. It was first noticed by Oerstedt in 1819, and afterwards more minutely examined by Pelletier in 1821. It may be obtained in the following way:

Boil pepper in alcohol. Evaporate the tincture to dryness, and wash the residue with water. What remains undissolved by the water is to be dissolved in hot alcohol. Set the solution aside for a few days, that it may have time to deposit crystals. These crystals, by washing in cold alcohol, and subsequent solution in hot alcohol or ether, and crystallization, are to be freed from a greenish-white resin. Such is the process of Pelletier: other processes have been proposed by Buehner, Mcli, Pfeil, Henkenius, and Winkler.

It crystallizes in oblique four-sided prisms, whose faces are inclined to each other at angles of about 85° and 95°. When heated to about 212° it melts into a light-yellow transparent oil, which hardens on cooling into a light-yellow, translucent, resinous-like matter. It has very little taste, and what it has is probably derived from a little of the oil of pepper, of which it is not easy to free it. It is insoluble in cold, and only slightly soluble in boiling water. It is very soluble in alcohol, less so in ether; but dissolves better in these two liquids when hot than while cold. Acetic acid is also a good solvent of it. Dilute sulphuric, nitric, and muriatic acids do not act sensibly on it; but when these acids are concentrated they alter its nature. Concentrated sulphurie acid gives it a blood colour, but the colour disappears if the acid be diluted with water. Muriatic acid acts in the same way, only the colour produced is not red, but an intense yellow. Nitric acid renders it first greenish yellow, then orange, and at last red. By long continued action oxalic acid and a bitter matter are formed. When distilled it produces water, acetic acid, oil, carburetted hydrogen gas, but no ammonia. Though, from the experiments of Oerstedt, we have placed piperin among alkaline bodies, there is reason to believe, from the subsequent researches of Pelletier, that its properties are not alkaline, but that it approaches nearer to resins. If so, it is rather an acid than an alkaline body.

Sect. XXV.— Of Plumbagm.

This substance was discovered by Dulong, in the root of the plumbago Europcea in 1828. It may be obtained by the following process:

The roots, not too woody, are digested in lukewarm ether. After separating the solution, distil off the ether, and boil the dry residue in water. Plumbagin and gallic acid will be taken up. Filter the liquid boiling hot; on cooling, flocks of plumbagin are deposited. Decant the liquid off these flocks, and boil it again on the black residue. The liquid being again filtered while boiling hot, and allowed to cool, deposits more plumbagin. This process is to be repeated several times, till the residue is exhausted of plumbagin. By dissolving the plumbagin two or three times successively in cther, or in alcohol mixed with ether, it is deprived of the gallic acid with which it is at first contaminated.

It crystallizes in soft, oblique, lemon-yellow needles, when the ethereal or alcoholie solution is concentrated. From a saturated aqueous solution it falls in flocks. When gently heated it melts, and concentrates on cooling into a yellowish, fibrous mass. It may be partly volatilized without decomposition.' Its taste is sharp and hot, though, according to Derohne and Henry, the first impression is that of sweetness.

It is very little soluble in cold water. In hot water it is more soluble, communicating a lemon-yellow colour to the liquid, and being again deposited in crystalline flocks when the liquid cools. It is soluble in alcohol both cold and hot, and is precipitated in flecks by the addition of water. It is soluble also in ether. It dissolves in sulphuric acid with a lemon-yellow colour; the addition of water throws it down in yellow flocks, but an additional dose of water takes them up again. The same phenomena take place with nitric acid.
[7:6:470]

The addition of a little ammonia or fixed alkali increases the solubility of plumbagin in water, communicating at the same time a cherry-red colour. Lime water produces the same change of colour. Diacetate of lead dropt into an aqueous solution of plumbagin occasions a kermes red precipitate, and leaves the liquid of a red colour. Sulphate of copper communicates a reddish colour, and very dilute perchloride of iron strikes a dirty-red colour. Tartar-cme-tic, nitrate of lead, acetate of lead, nitrated suboxide of mercury, have no action on it.

Sect. XXVI.— Of Jamaicin.

This substance was detected in 1824, by Hüttenschmid, in the bark of the Geoffroya Jamaicensis, or cabbage-bark tree of Jamaica. It may be prepared by the following process:

Boil the bark repeatedly in alcohol of the specific gravity 0∙832. From the filtered decoctions distil off the alcohol. Dissolve the residue in water, and filter the liquid. Mix it with acetate of lead as long as any precipitate falls, and throw down the excess of lead by a current of sulphuretted hydrogen gas. Filter the liquid, and add a little sulphuric acid to it. Sulphate of Ĵamaicin falls in small grains. Concentrate the residual liquid till as many of these crystals as possible are obtained. Dissolve the sulphate of Ĵamaicin in water, and digest the solution with carbonate of barytes, till all the sulphuric acid is abstracted. Filter while boiling hot, and concentrate the solution till the Ĵamaicin is deposited in crystals.

The crystals are lemon yellow, translucent, four-sided tables; fusible below 212°; very bitter tasted, and seem to possess purgative properties. They dissolve readily in water, and the colour of the solution is lemon yellow. The aqueous solution gives a yellow precipitate with tincture of nutgalls. It dissolves also in alcohol. It possesses alkaline qualities, dissolves in acids, and forms-salts. The phosphate, sulphate, nitrate, and muriate crystallize. They have a bitter taste; they are soluble in water and alcohol, and burn when sufficiently heated. The oxalate and acetate are also capable of crystallizing.

Sect. XXVII.— Of Słirinamin.

This substance was also obtained by Hüttenschmid, from the bark of the Geoffroya Surinamensis.

To prepare it, digest the bark in alcohol, and from the alcoholic solution distil off the spirit. Digest the remaining extract in water, and mix the solution with acetate of lead. Filter and throw down the excess of lead by means of sulphuretted hydrogen gas. Filter again, and then evaporate the solution. A portion of surinamin precipitates. The rest may be obtained by digesting the liquid with magnesia, filtering, and further evaporation.

It is in white, bulky, woolly needles. Its taste is slight but disagreeable, and, when given to the extent of two grains, it had no sensible action on a pigeon. It is but little soluble in cold, but moderately soluble in hot water. The aqueous solution is not altered by iodine, ammonia, nitrated suboxide of mercury, and the tincture of nutgalls. In hot alcohol it is less soluble than in water. In dilute sulphuric acid it dissolves with facility. The solution is light red, tastes like sulphate of magnesia, and yields crystals. The muriatic solution of surinamin also yields crystals.

When heated in a tube it gives out first a smell resembling bruised plums, and at last gives out a vapour containing ammonia, and leaves a bulky charcoal. When dissolved in nitric acid, the solution is at first violet, and at last Berlin blue. In forty-eight hours the colour vanishes, and violet-coloured flocks are precipitated.

Sect. XXVIII.— Of Asparαgin.

This substance was discovered in 1808, by Vauquelin and Robiquet, in the juice of asparagus sativus, or common asparagus. It was afterwards discovered in marshmallow-root by Bacon, and in liquorice-root by Robiquet and Plisson. The juice of the asparagus is expressed in the usual way, filtered, evaporated to the consistence of a . syrup, and then set aside. Crystals of asparagin are gradually deposited.

The crystals are white, and are four-sided oblique prisms, whose faces are inclined to each other at angles of 130° and 50°. It is hard and brittle. Its taste is cooling and disagreeable. It does not produce any change on vegetable blues. It dissolves pretty well in water, but is insoluble in alcohol unless it be diluted with water. The aqueous solution is not affected by sulphohydrate of potassium, oxalate of ammonia, chloride of barium, acetate of lead, and tincture of nutgalls.

When heated, it swells and emits penetrating vapours, affecting the eyes and nose like the smoke of wood. Nitric acid dissolves it with the evolution of nitrous gas. The solution has a yellow colour and a bitter taste, like that of an animal substance in the same acid. Lime disengages a considerable quantity of ammonia.

The evidence that asparagin is an alkaline body is far from being complete.

Sect. XXIX.— Of Salicin.

This principle has lately been discovered in the bark of the salix alba, or white willow, by M. Leroux. It has much analogy in its medical properties to quinin, and, like it, is found an effectual remedy for intermittent fever. The bark of the salix monandra, after it has reached the age of three years, appears, from the experiments of Μ. Leroux, to be much richer in salicin than that of the salix alba. It may be procured in the following manner:

The dried bark is to be reduced to a coarse powder,] and boiled in water for a couple of hours. The decoctiont is to be filtered, and the bark subjected to pressure. Mix the liquid thus obtained with diacetate of lead as long as any precipitate continues to fall. Filter and boil the liquid with carbonate of lime till all the excess of lead added be thrown down, and acetic acid present be saturated. Decant off’ the clear liquid, and wash the sediment two or three times, and, mixing the whole liquids together, evaporate to the consistence of an extract. Expose the extract to pressure between folds of blotting paper, and expose the dry matter remaining to the action of alcohol of the specific gravity 0 ’ 837. Filter and concentrate by distilling off the alcohol. The salicin precipitates in crystals having a pearly lustre.

The taste is very bitter, and there is also something aromatic, like that of the bark of the willow. A hundred parts of water at the temperature of 67° dissolve 5 ’ 6 parts of salicin. Hot water is a much better solvent, and boiling water dissolves it in any proportion whatever. It is soluble also in alcohol; but ether and oil of turpentine do not take up the smallest quantity of it.

Concentrated sulphuric acid, poured on salicin, gives it a very beautiful red colour, very similar to that of bichromate of potash. It dissolves in nitric and muriatic acids without acquiring any colour. The solution is not precipitated by nutgalls, gelatine, acetate or diacctate of lead, alum, or tartar emetic.

When boiled in excess with lime water, no combination takes place; nor is it capable of dissolving'oxide of lead. When heated a few degrees above the terpperature of boiling water, it melts, and,on cooling assumes a crystalline form. When thus treated it loses no water. If it be [7:6:471] exposed to a higher heat it assumes a lemon-yellow colour, and becomes brittle like a resin.

It was analysed by MM. Pelouze and Jules Gay-Lussac, who found its constituents as follows:
[table]

As no attempts have been made to determine the atomic weight of salicin, we cannot, from this analysis, determine its atomic constitution; but the smallest number of atoms corresponding with these proportions is,
[table]

Its atomic weight, then, is 31∙375, or some multiple of that number.

Sect. XXX.— Of Populm.

This substance was detected in 1830, by Μ. Braconnot, in the bark of the populus tremula. He found afterwards that the leaves of that tree furnish it in greater abundance. It may be extracted by the following process:

Boil the leaves in water, and pour into the solution diacetate of lead. A fine yellow precipitate falls. Filter the liquid, and evaporate it to the consistence of a syrup. When it cools, the populin separates under the form of a very bulky crystalline precipitate. Expose it to strong pressure between folds of linen cloth; then heat it with a hundred and sixty times its weight of water and a quantity of ivory-black, and filter the liquid while boiling hot. On cooling it deposits abundance of very fine silky needles. When dried on blotting paper it is a very light matter, having a snow-white colour.

Populin has a swect taste, not unlike that of liquorice. It requires about two thousand times its weight of cold water to dissolve it. The aqueous solution is not affected by most of the metalline salts; but chloride of sodium throws it down unchanged, and in the form of crystals. It is soluble in seventy times its weight of boiling water. Boiling alcohol dissolves it in much greater proportion, and when the liquid cools it is totally converted into a crystalline magma. It is very soluble in acetic acid and nitric acid, and it may be precipitated from these solutions by the alkalies. Phosphoric acid dissolves it also; but when that acid is too concentrated, it converts it at once into a resin. The weak mineral acids, when hot, act upon it as they do on salicin; they convert it into a white resinous powder, perfectly similar to that produced from salicin. Like salicin, it gives a purple-red solution with concentrated sulphuric acid.

When treated with nitric acid it furnishes, as salicin does, a great quantity of crystallized carbazotic acid, but no oxalic acid. When heated sufficiently with potash it is converted into oxalic acid, as is the case with all organic bodies. When heated, it first melts into a transparent and colourless liquid; it then burns with a strong flame, giving out at the same time an aromatic odour. By distillation it would seem to yield an empyreumatic oil and benzoic acid.

How far this substance is alkaline has not been examined, but its ready solution in acids seems to favour that notion.

Sect. XXXI.— Of Colombia.

This substance has been lately discovered by Wittstock, in the root of the Colombo. He considers it as the active principle of that plant. We have not yet seen any description of it.

It is crystallized in small needles, and has a very white colour. Liebiu analysed it, and found its constituents
[table]

It contains no azote. As no attempt has been made to determine the atomic weight of colombin, we cannot give its atomic constitution; but the smallest number of atoms which corresponds with the above analysis is,
[table]

so that its atomic weight approaches 31∙5, or some multiple of that number.

Sect. XXXII.— Of Mudarin.

This substance has been recently detected by Dr Duncan, in the bark of the root of the calotropis mudarii, or mudar. Its alkaline qualities have not been made out, but we place it here in consequence of its bitter taste, which assimilates it to many of these bodies. It may be obtained by the following process:

Digest the powdered root in cold rectified spirits. When the greater part of the spirit has been distilled off, the liquid becomes darker coloured, but retains its transparency. As it cools, a white granular resin is deposited. Let the liquid evaporate spontaneously to dryness, and digest the dry matter in cold water, which dissolves the coloured portion, and leaves the resin. This solution consists chiefly of mudarin.

When evaporated spontaneously to dryness, it forms a transparent brown-coloured matter, not crystalline, but cracking in all directions, and not adhering to the vessel in which it formed. It has no smell, but an intensely bitter and nauseous taste. It is very soluble in cold water, but much less soluble in that liquid while hot. It dissolves also in alcohol, and the solubility increases with the temperature. In ether, oil of turpentine, and olive oil, it does not dissolve.

When a saturated solution in cold water is heated to 74°, it becomes slightly opal. At 90° the transparency is nearly gone, and the liquid assumes the form of a jelly; but if allowed to cool, it becomes, in a day or two, as liquid and transparent as ever. At 95°, a soft, brownish coagulum begins to separate from a liquid nearly colourless, and the coagulum contracts in size as the heat increases; so that at 212° it has the consistency of pitch. This matter dissolves very slowly in water; yet that liquid takes it upas completely as at first, if time be allowed for its action.

No trials seem to have been made respecting the solubility of this substance in acids. Indeed we have no evidence that the mudarin, as examined by Dr Duncan, was pure.

CHAP. III. OF NEUTRAL VEGETABLE PRINCIPLES.

These substances exist in great abundance in plants, and may be considered as the principal ingredients of which they arc composed. It has not yet been ascertained that they possess either the characters of acids or of alkalies. This ignorance of any definite compounds into which they can enter stands, very much in the way of the attempts which have been made to determine their constitution[7:6:472], and renders all knowledge of their atomic weight quite uncertain. It is not unlikely that not a few of these bodies will be arranged hereafter either among acids or alkalies, when they come to be more completely investigated. Sugar, gum, and several of the resins, appear to be acids; while starch and lignin bear a closer'relation to alkaline bodies. But till these analogies be more closely investigated, we must be satisfied with arranging them under the name of neutral or indifferent substances. These substances will occupy our attention in the following sections.

Sect. I.— Of Sugar.

Sugar exists, though in no great quantity, in a great variety of vegetables; and as every vegetable principle distinguished by a sweet taste has been called sugar, there can be no doubt that substances possessed of very different properties have been confounded together under the same name. The most important of all the species of sugar is that extracted from the sugar-cane, employed in this country as a common article of food. We shall therefore describe it in the first place, and afterwards point out the characters of the other species, so far as they have been ascertained.

1. Cane Sugar. — It is obtained from the arundo sacchari-fera, saccharιιm officinarum, or sugar-cane, which seems to be a native of India and China, but has been long cultivated to a great extent in the West Indies. Good sugar-canes give about half their weight of juice, by boiling which, the sugar is obtained in small grains or crystals. It is afterwards refined in this country, and converted into the beautiful white crystalline mass known by the name of loaf sugar. Its taste, is a strong and agreeable sweet. Its colour is white, and when properly crystallized it is translucent or semitransparent. The crystal is an oblique four-sided prism, whose base is a rhomb, the length of which is to its breadth as ten to seven, and whose height is a mean proportional between the length and breadth of the base. These crystals contain water, and appear to be composed of
[table]

The specific gravity of sugar is 1∙5629. It is soluble in the third part of its weight of cold, and in any proportion whatever of hot water. The concentrated solution is called syrup. It is thick and adhesive, and may be employed to agglutinate pieces of paper together. It is soluble in eighty times its weight of absolute alcohol; but as the solution cools, the greater part of the sugar is deposited in crystals. It is soluble in four times its weight of boiling alcohol of the specific gravity 0 ’ 830, and the solubility increases with the weakness of the spirits.

It is not altered by exposure to the atmosphere; if the air be damp, however, it is apt to absorb moisture.

When heat is applied to sugar, it melts at 250°, then swells, becomes brownish black, emits air bubbles, and exhales a peculiar smell known by the name of caromel. At a red heat it instantly bursts into flame with a kind of explosion. The colour of the flame is white, with blue edges.

Sugar seems to have the property of entering into combinations with the bases, and of forming definite compounds which have some analogy to salts. The following are the principal of those which have been noticed.

lsí, Saccharate of Ammonia. Twenty parts of sugar absorb one part of ammoniacal gas, and is changed into a thick, flexible, shining, crystalline mass, smelling of ammonia. It is a bisaccharate, composed of
[table]

2d, Saccharate of Potash. Sugar dissolves in potash ley, and forms a liquid having not the least sweetness. When boiled to the thickness of a syrup, it is not miscible with alcohol; but if the potash be neutralized by sulphuric acid, boiling alcohol is capable of again extracting sugar from it.

3rZ, Saccharate of Strontian. When equal quantities of strontian and sugar are dissolved in hot water, the solution has a light-yellow colour and a caustic taste. On cooling it deposits crystals which absorb carbonic acid from the atmosphere. These crystals are probably nothing else than hydrate of strontian.

⅛th, Saccharate of Lime. Lime dissolves in syrup in far greater quantity than in pure water. When the solution is slowly evaporated, it deposits four-sided prisms. It has a bitter and alkaline taste, but no sweetness. It would appear from Daniel’s observations that lime has the property of gradually decomposing sugar, and of converting it into a substance analogous to gum.

ĩ>th, Saccharate of Lead. When a solution of sugar is digested on oxide of lead, the oxide is gradually dissolved; but after a certain interval a light white powder makes its appearance. This is saccharate of lead. According to Prout, it may be obtained in crystals. Its constituents, as determined by Berzelius, are,
[table]

There is reason, from the composition of the crystals of sugar, to consider its atomic weight as 20 ’ 25. If so, the saccharate here analysed was obviously a disaccharate, composed of
[table]

6/7«, Saccharate of Copper. Syrup dissolves black oxide of copper rather abundantly. The solution is green, and it is not precipitated by the alkaline carbonates, but the copper is thrown down by the common precipitate of potash.

Sugar has been repeatedly and carefully analysed by different chemists. The following little table exhibits its constituents, according to the various experimenters.
[table]

The number of atoms that agree best with the analysis of Prout is as follows:
[table]

But this does not fully accord with the atomic weight deduced from the analysis of the crystals of sugar and disaccharate of lead. It would be necessary to add another atom of carbon, which would raise the proportion of carbon[7:6:473] to 44Ţ per cent, considerably exceeding that deduced from any of the preceding analyses. Hence it is likely that the true atomic weight of sugar does not exceed 19∙5.

Maple sugar, and the sugar extracted from beet, carrot, &c. are precisely of the same nature with that from the sugar-cane. z 2. Sugar of Figs. — The sugar of figs may be seen in a concrete state on the outside of that fruit as it is commonly sold in this country. When we dissolve this fruit in boiling alcohol, and set the solution aside with a small piece of wood or a quill in it, we readily obtain the sugar in crystals. As the shape of these crystals is quite different from that of common sugar, it obviously constitutes a peculiar species; but its characters have not yet been determined.

3. Sugar of Grapes. — This sugar is obtained from the juice of ripe grapes, which in a good year contain from thirty to forty per cent, of solid matter, the most of which consists of sugar. The acid which it contains must be, in the first place, saturated with chalk. Draw off the clear juice, mix it with 'white of egg, and boil. The scum which collects on the surface is to be taken off, and the liquid boiled till its specific gravity becomes l∙32. It is then set aside for two or three days, when a granular mass of sugar is deposited. The liquid portion is poured off. The crystals are a mixture of three parts solid sugar and one part syrup, and this syrup cannot be separated. By means of ivory-black it may be made white.

. Grape sugar crystallizes so imperfectly, that the shape of its crystals has not been made out in a satisfactory manner; but it is different from that of common sugar. It is usually in very minute needles, collected together in small spheres. Its taste resembles that of honey. It contains much more water than common sugar. It melts at 212°, or a little higher, and loses about eight per cent, of its weight. On cooling it constitutes a yellowish translucent mass, which attracts moisture from the atmosphere.

It is not so soluble in cold water as common sugar, requiring once and a third of its weight of that liquid dissolve it. In Boiling water it is very soluble; but the syrup has not the same consistence as common sugar, and cannot be drawn into threads. The solution is sweeter than the sugar itself. It may be kept without alteration; but if we mix it with yeast it ferments, and the sugar is gradually decomposed into alcohol and carbonic acid. It is much less soluble in alcohol than common sugar.

Its affinity for salifiable bases is much weaker than that of common sugar, yet it unites with them, and forms compounds having a bitter taste. If we add an excess of the base, and heat the liquid to 140° or 160°, the sugar becomes brown, and gives out the smell of caramel; When saturated with lime it is converted into a slimy matter, from which alcohol throws down white curdy flocks. These, when dried, become Reht brown, and are composed of
[table]

Saussure analysed this sugar, and found it composed of
[table]

The atomic constitution which agrees best with this analysis is the following:
[table]

Thus it would contain two atoms less carbon and half an atom more oxygen. But no confidence can be put in this estimate till satisfactory experiments have been made to determine its atomic weight.

4. Sugar of Starch. — When starch is boiled in water acidulated with sulphuric acid, employing one part of starch for every four of water, replacing the water as it evaporates, and continuing the boiling till it is found that when a few drops of the liquid are mixed with twice its volume of alcohol no precipitate falls, the starch is converted into sugar. The length of time necessary for this conversion depends upon the proportion of sulphuric acid present. If it amount to one per cent, of the water, thirty-six hours’ boiling will be required. Two and a half per cent, of acid reduces the time to twenty hours, while ten per cent, reduces it to seven or eight hours. The boiling may take place in a copper or wooden vessel. To obtain the sugar from this liquid, we must saturate the acid with chalk, and filter. The liquid is to be then boiled to a thin syrup, and afterwards allowed to shoot into crystals. In three days it is generally all converted into a yellowish granular mass, without any mother liquid. We may obtain it quite white if we digest the liquid before concentrating it with ivory-black.

During this process nothing is abstracted, from the atmosphere nor from the water. The process goes on equally well in close vessels as in open vessels. The acid is not altered, and the weight of the sugar exceeds that of the starch employed. Saussure found that 100 parts of starch became 110∙14. The shape of the crystals, according to Saussure, is a small table, or cube. The properties of starch sugar, so far as known, are the same as those of sugar of grapes. The presence of gluten seems to prevent starch from being converted into sugar by boiling it in dilute sulphuric acid, for neither flour nor meal can in this way be converted into sugar. Yet, when barley meal is infused in hot water, it is well known that the infusion becomes sweet; for it can be fermented into beer. Malt (which is barley germinated) is converted into sugar by simple infusion in hot water. It has not been made out yet by decisive experiments that this sugar is the same with starch sugar; but it is very probable that it is. Starch, in its conversion into sugar by sulphuric acid, seems to pass through the state of gum. The constituents of starch sugar, according to the analysis of' Saussure, are the following:
[table]

These numbers agree best with
[table]

But whether the difference between this analysis and that of sugar of grapes, which lies chiefly in the oxygen, results from an error in the analysis, or from a real difference in the constitution of the two sugars, cannot at present be determined.

The crystallizable sugar of honey is considered at present as identical with sugar of grapes, though we are not aware of any series of experiments by which that identity has been established.

5. Mushroom Sugar. — This sugar may be extracted from the agaricus volvaceus, and several other mushrooms. It crystallizes in rectangular prisms with square bases. It has such a disposition to crystallize, that when a very [7:6:474] weak aqueous solution of it is put upon the surface of a vessel, it is immediately sprinkled with small acicular crystals. When heated this sugar melts, swells, and takes firc, giving out the odour of caramel. There remains a small quantity of charcoal, which is destitute of alkali. Acids do not deprive this sugar of the power of crystallizing, as they do common sugar. When digested with nitric acid it produces abundance of oxalic acid. It is capable of undergoing the vinous fermentation.

6. Manna. — Manna is the produce of a great variety of trocs, and even of other plants; but the manna to be met with in apothecaries’ shops is chiefly the produce of the fraxinus ornus, a species of ash which grows abundantly in Sicily and Calabria. It flows out during summer in the state of a clear sap, which gradually concentrates into drops, and then constitutes manna. A good deal exudes from the larch, but so mixed with turpentine that it cannot be employed.

• Pure manna is very light, and appears to consist of a congcrics of fine capillary crystals. Its taste is sweet, but rather nauseous, in consequence of a foreign matter with which it is contaminated. It is easily obtained pure by dissolving it in hot alcohol to saturation, and setting the solution aside. The pure manna is deposited in a white spongy crystalline mass, bearing some resemblance to camphor. Its taste is agreeably sweet, and it melts on the tongue like snow.

The crystals arc fine translucent four-sided needles. It dissolves very readily in alcohol, and crystallizes on cooling. When digested in nitric acid it yields both oxalic and malic acid. Its solution does not ferment like that of sugar, hence it seems incapable of furnishing alcohol. It was analysed by Saussure, and by Prout, who obtained from it,
[table]

The atomic proportions agreeing best with Dr Prout’s analysis are,
[table]

This is the same atomic weight as we found for common sugar, though the constitution of manna is obviously different. But no conclusion can be drawn from these analyses till we have obtained definite notions respecting the atomic weight of manna, and till we know whether the crystals contain any water.

7. Liquorice Sugar. — This substance is obtained from the roots of the glycirrhyza glabra, or common liquorice, a plant cultivated in the south of Europe, and cven in England. The decoction of these roots inspissated by boiling is known by the name of black sugar, or liquorice sugar. To obtain pure liquorice sugar, the following process may be followed:

Macerate liquorice roots in boiling water, and concentrate the liquid in a very gentle heat. Then mix it with sulphuric acid, which will occasion a white precipitate, consisting of liquorice sugar mixed with albumen. Let the precipitate be washed in water acidulated with, sulphuric acid, and at last .with a small quantity of pure water. Alcohol will now dissolve the sugar, and leave the albumen behind. To the solution add cautiously carbonate of potash til] the liquid loses its acid, characters. Then filter and evaporate. The sugar remains under the brm of a yellow translucent brittle mass, which does not ιdhere to the vessel. In nearly the same way may it be extracted from the common black sugar oĩ commerce.

When in powder it resembles pounded amber. Its taste s sweet, with a peculiar flavour which is well known to characterize liquorice. It dissolves readily both in water and alcohol. It cannot be deprived of its yellow colour by ivory-black. When heated it swells like borax; and taking fire it burns with a clear flame, emitting much smoke.

Its most remarkable characters are the strong affinity which it has for acids, bases, and even for several salts.

With acids it forms compounds, which are nearly insoluble in water; hence the addition of an acid throws it down from its aqueous solution. Sulphate of liquorice sugar is a glutinous, resinous-looking substance, which, when dried, becomes yellow and translucent. Its taste is simply swcet, like that of the sugar; but it dissolves much more slowly in the saliva. It dissolves in boiling water, and is deposited in a gelatinous state as the liquid cools. It is soluble in alcohol; and when the solution is evaporated it leaves an opaque, straw-yellow matter. It burns precisely like the pure sugar, and leaves no ashes.

Acetate of liquorice sugar is pretty similar to the sulphate, but much more soluble in boiling w ʹ ater.

So great is the tendency of liquorice sugar to unite with bases, that we must take care not to add more of a base than is just necessary to saturate the acid with which il was in combination, otherwise the sugar will be sure t( unite with the excess. When a solution of liquorice su gar is digested with a carbonate, the carbonic acid is giver off, and the sugar combines with the base. M hen the suga is exactly saturated, the taste is simply sweet. The com pounds thus formed are soluble in water, and likewise iι alcohol, though in less quantity. None of these com pounds crystallizes. . ∣

Sulphate of potash, nitrate of copper, acetate of lead sulphated peroxide of iron, chloride of tin, &c. may b( combined with liquorice sugar; but it occasions no preci pitate in a solution of corrosive sublimate.

No attempts have yet been made to determine the ato mic weight, or to analyse liquorice sugar.

8. Glycerine. — This is the name given by Chevreul t( the substance discovered by Scheele, and called by hin the sweet principle of oils. It may be obtained by mixing together one part of protoxide of lead and one part of hog’s lard, and boiling it with water for some time. Tin water is to be drawn off from time to time, and new water added. The aqueous solution contains the glycerine iι combination with oxide of lead, from which it may b( freed by a current of sulphuretted hydrogen gas. Lei the liquid be now filtered and evaporated on the vapouι bath. .

Thus prepared, it is a colourless or yellowish syrup, which will not crystallize; has a sweet taste, and no smell. When as much concentrated as possible by a beat of 212°, its specific gravity is 1*252; and after being left for a month in a vacuum over sulphuric acid,· it lost six per cent, o∣ water, and its specific gravity became I ’ 27. According to Chevreul, a small portion of glycerine maybe distilled over with boiling water. This substance was analysed by Chevreul, who found its constituents
[table]

These numbers agree best with the following atomic pro portions: κ - . , , > , H '∙ '
[7:6:475]
[table]

It seems to contain more hydrogen and less oxygen than any of the other species of sugar; but no great confidence can be put in the accuracy of the analysis on which the preceding calculation is founded.

The preceding enumeration does not include all the varieties of sugar hitherto observed; but the rest have been so imperfectly studied, that we cannot as yet describe them. About fifteen years ago a sweet substance like manna was brought from Botany Bay. It had been gathered in a plain covered with wood, and doubtless had been an exudation from some plant. Its solubility in alcohol was the same as that of manna, but the shape of its crystals did not agree with that of manna, nor did it make so cooling an impression on the tongue. It was probably a variety of manna; but the small quantity brought to London did not permit any thing like a rigid examination.

The substance found by Petroz and Robinet in the ca-nella alba, to which they have given the name of canellin, is probably another species of sugar; but the description is too imperfect to enable us to give any account of it here.

Sect. II.— Of Starch.

This principle is one of the commonest in the vegetable kingdom. It constitutes a portion of the seeds of almost the whole tribe of grasses, and of many other plants, besides almost all the bulbs, as potatoes, iatroplia manjhot, helianthus tuberosus, &c. It exists also in the pith of various palms, as the sagus rumpbii, cycus revoluta, and circinalis, but seldom in the pith or stems of bicoyledonous plants. The leaves also of plants very frequently contain it. There are several varieties of it, but the type of the whole is common starch, whether extracted from wheat or from potatoes.

1. Common Starch. — Common starch is usually made from wheat by the following process: Good wheat is allowed to steep in water till it becomes soft, and yields a milky juice when squeezed. It is then put into coarse linen sacks, and subjected to pressure in a vat filled with water; a milky juice exudes, and mixes with the water in the vat. This process is repeated so long as the wheat will yield any milky juice. The sack and its contents are then removed. Fermentation takes place, alcohol and an acid are generated, which dissolve all the impurities, leaving nothing behind but pure starch. The starch, after being washed, is dried. In drying, it splits into small columnar masses, which have considerable regularity. Very pure starch may also be obtained from the potato, simply by grating down the potato, and washing it on a seirce: the water carries the starch with it, leaving the fibrous part of the potato behind.

. Starch is a beautiful white matter, composed of small grains, having considerable lustre, and probably a crystalline structure. It is insoluble in cold water, but when boiled with water it is converted into a translucent jelly. If this jelly be thin, and set aside for some time, it begins to subside, and falls very slowly to the bottom. If infusion of nutgalls be poured into this jelly, a light brownish-red precipitate falls. If the liquid be heated up to 120°, this precipitate dissolves; but it appears again when the liquor cools. This properly characterizes starch, and enables us to detect its presence.

Starch is insoluble in alcohol and ether. When boiled in dilute sulphuric acid it is converted into sugar. The same change takes place partially when the infusion of starch in water is left to spontaneous evaporation. When digested in nitric acid, starch is converted into malic and oxalic acids, without the least trace of mucic acid.

The aqueous infusion of starch is precipitated by diacetate of lead.

When heated so high as to change its colour a little, without being burnt, it acquires the smell of new bread, and becomes completely soluble in water. When the aqueous solution is evaporated, a substance so like gum is obtained, that it may be used by the calico-printers, and is known in commerce by the name of British gum.

When heated rapidly, starch undergoes a kind of semifusion; it is charred, smokes, and burns with a lively flame.

Starch absorbs chlorine gas, and assumes at the same time a brown colour. With bromine it combines and forms an orange-coloured precipitate. With iodine it strikes a deep blue, and is in consequence a very delicate re-agent for discovering the presence of that substance.

The dilute acids dissolve starch, and the solution is clear and quite liquid. By long boiling the starch is converted, first into gum, and then into sugar.

It has a stronger affinity for the bases than for acids. When triturated with caustic potash, it is converted into a transparent jelly, soluble both in water and alcohol, and from this solution the starch is precipitated by acids. When the jelly is diluted with much water it becomes opal. When the infusion of starch is mixed with barytes or starch water, a precipitate falls, consisting of these bodies united with starch. In the same way we may obtain a compound of starch and oxide of lead, by mixing diacetate of lead with the infusion. The precipitate is white, curdy, and heavy. According to the analysis of Berzelius, it is composed of
[table]

We know little of the action of salts upon starch. The infusion of starch is coagulated by borax. When the infusion is boiled with phosphate of lime, it dissolves a portion of that salt. There is a light-blue compound of prussian blue and starch commonly sold under the name of blue, and used by washerwomen.

Starch has been analysed with considerable care by chemists. The following little table shows the results of these analyses:
[table]

The atomic numbers that agree best with the last analysis in this table are,
[table]

But if we take the second analysis, the numbers agreeing best with it are
[7:6:476]
[table]

Now the difference between the two was, that in the one case the starch was dried at 212°, and in the other in a vacuum over sulphuric acid. Prout dried starch at 212°, and obtained nearly the same results. Had the oxygen been a little higher than it is in Berzelius’ analysis, it would be evident that by the temperature of 212° two atoms of water had been driven off. As it is doubtful whether this water existed in the starch in that state, or whether its evolution was not owing to a commencement of decomposition, we cannot, in the present state of our knowledge, form an adequate idea of the composition of starch. It is most probably a compound of
[table]

This approaches very nearly to the component parts of sugar, and renders it not unlikely that sugar and starch differ not in the number and nature of their atomic constituents, but in the way in which they arc arranged.

2. Hordein. —-When barley-meal is washed in a small current of water in the same way as wheat flour, in order to extract the gluten, instead of that principle there remains a great quantity of matter, which Prout distinguished by the name of hordein. It is a yellow granular powder, like saw-dust. As it is not soluble in water, it may be freed from starch by boiling the residue of washed barley-meal (about 80 per cent.) in water. The residuary hordein amounts to about fifty-five per cent, of the barleymeal from which it was extracted. When distilled it yields, together with gaseous bodies, acetic acid, and an empyreumatic oil, and leaves the fifth part of its weight of charcoal. When digested in nitric acid it furnishes oxalic acid, acetic acid, and a little bitter principle. Prout is of opinion that during malting the greater part of this substance is converted into starch. It exists also in maize. The constituents of hordein, according to Mr F. Marcet, arc,
[table]

The atomic proportions agreeing best with these numbers are,
[table]

According to this analysis (if we admit a little ammonia, or its elements), hordein differs from starch by the absence of an atom of water, or at least of its constituents.

3. Inulin. — This substance was discovered by Valentine Rose in the root of the inula helenium, or elecampane. It has been since found in the roots of angelica arcbangelica, anthémis pyrethrum, Colchicum autumnale, georgina (dahlia) purpurea, helianthus tubcrosus, and it probably exists in the roots of all the asters. It has been called helenm, alantin, datiscin i and dahlin. It exists most abundantly in the root of the georgina; but it may be easily extracted from the roots of elecampane or arti choke. Grate down the root and boil it with water. Filter the decoction while boiling hot. If it is not clear iι may be clarified by white of egg. Let it now be evaporated till a film collects on the surface. On cooling, the inulin precipitates in the form of a powder. Let it be col lected on a filter, and well washed and dried. From th< georgina we can extract ten per cent, and from the artichoke three per cent, of inulin.

It constitutes a light and very white powder, withoul taste or smell, and having a specific gravity of 1∙356 When heated a little higher than 212°, it loses water and melts. On cooling it assumes the appearance of a grayish sealymass, which may be easily reduced to powder. Its characters are now very nearly the same as those of starch Iodine gives it a yellow colour, and makes it soluble in cold water.

It is very little soluble in cold water, a hundred parts of that liquid dissolving only two of inulin; but boiling water dissolves it abundantly. The solution is mucilaginous, but has not the property of pasting pieces of paper together. When the solutiorr is boiled the inulin forms a crust on the surface, and on cooling it falls in the form of a powder. When inulin is roasted, it is converted inte hard translucent lumps like sago.

It is insoluble in cold alcohol, and precipitated by il from water; but boiling alcohol dissolves a little of it and allows it to fall again on cooling.

It is dissolved readily by dilute acids. When boiled with dilute sulphuric acid, it is more readily converted into sugar than starch itself. Nitric acid converts it inte malic and oxalic acids. It combines'with the bases precisely as starch does. The action of the infusion of nutgalls is precisely the same on inulin as on starch.

No attempt has been made to analyse inulin; but its constitution cannot differ much from that of starch.

4. Lichen Starch. — Different species of lichens contain a starch very similar to common starch, except that it has nothing of the powdery form which common starch so readily assumes. Iceland moss, the cetraria islandica of Acharius, contains it in greatest abundance; but it is found also in the lichen plicatus and barbatus. From Iceland moss it may be obtained in the following way:

Let the moss be chopt fine, and digested in eighteen times its weight of water having about the thirtieth part of its weight of potash dissolved in it. Let this mixture remain for twenty-four hours, often stirring it during that time. The alkali dissolves a bitter matter, nearly insoluble in pure water, and the liquid acquires a dark-brown colour. The lichen is now laid upon a linen cloth, to allow the lcy to run off. It is afterwards well washed with water till it is quite freed from every trace of the alkali. We must not apply pressure, otherwise we would lose a good deal of the starch. The lichen is now to be boiled in nine times its weight of water, till the liquid be reduced to two thirds of its original bulk. Filter while boiling hot, and subject the residue to pressure. The filtered liquor is transparent and colourless. As it cools, a skin forms on its surface, and it at last assumes the form of a translucent-grayish jelly, which gradually contracts and cracks, and lets the water ooze out. If we suspend it in a linen bag the water drops out, and it gradually hardens. When fully dried it is black, hard, and breaks with a glassy fracture. When put into water, it swells and loses its black colour, which proceeds from an extractive matter that does not dissolve. If it be now dissolved in boiling water, it gives after cooling a colourless, translucent jelly.

It is destitute of taste, but has a slight smell of the lichen from which it was procured. It is insoluble in alcohol and ether. It contains no azote, and yields, when distilled or burnt, the same products as potato starch.
[7:6:477]

It is slightly soluble in cold water. When the solution of it in hot water is concentrated by boiling, it separates under the form of a skin on the surface of the liquid, which puts an end to the evaporation. One part of this starch forms a jelly with twenty-three parts of water. Chlorine does not alter it. Iodine gives it a colour between brown and green.

The weak acids dissolve it, and when boiled in dilute sulphuric acid, it is converted into sugar like common starch. Nitric acid acts on it as on common starch. It dissolves in caustic potash. It is not precipitated by barytes water, but by the disalts of lead. With the infusion of nutgalls it behaves like common starch.

The lichen fastigiatus and plicatus yield a starch differing in some of its characters from the starch of the lichen islandicus. *

5. Amylin. — When the infusion of starch in water is left to spontaneous decomposition, nearly one fourth of the starch disappears, sugar is'formed, and gum, and another substance intermediate between sugar and gum, to which Saussure has given the name of amylin or amidin. It is obtained from the residue, after every thing soluble in cold water is removed. Boiling water takes up the amylin, and leaves it in a state of purity, when it is evaporated to dryness.

It is semitransparent and brittle, and very soluble in water of the temperature 144°. This solution becomes blue when it comes in contact with iodine. It is coagulated by diacetate of lead, and copiously precipitated by barytes water, but not by lime water nor infusion of nutgalls. It dissolves in the aqueous solution of potash, and the solution has no viscidity. It is thrown down by acids and by alcohol.

There are some other substances obviously connected with starch. The fibrous starchy matter of the potato, for example, may be mentioned. Arrow root seems very nearly the same as potato starch. Sago and tapioea are also closely allied to the same substances. They owe their chief differences probably to the way in which they have been dried. The very nutritious article of food known in Scotland by the name of sowans consists chiefly of a starch from the seeds of oats.

Sect. III.— Of Gum.

This principle is still more abundant in the vegetable kingdom than starch; but hitherto the chemical properties of gum have been but imperfectly investigated. Hence it is not unlikely that different substances are at present confounded together under the name of gum. The principal characters are solubility in water, and the solution being possessed of a glutinous property, and being capable of pasting pieces of paper together, and stiffening linen. From the aqueous solutions the gum is precipitated by the addition of water. We know at least three distinct substances at present confounded together under the name of gum. We shall give a short account of each of these in the present section.

1. Gum Proper. — Gum exudes from a variety of trees in the form of a mucilage, and gradually dries on the bark in the form of a clear yellow or brown, hard, brittle concretion. Almost all plants contain some gum, which may be extracted by water; and when the liquid has been sufficiently concentrated, the gum may be thrown down by alcohol, though it seldom falls in a state of purity, but usually mixed with some other of the principles which the plant contains. Almost all the chemical properties of gum have been determined in gum-arabic, which is a gum under the form of small light amber-coloured and translucent tears, hard and brittle, and having a vitreous lustre. It exudes from the acacia vera.

It is destitute of smell, and has but little taste. Its specific gravity varies from 1∙32 to 1 ’ 48. It contains naturally no chemically-combined water; but when an aqueous solution of gum is evaporated to dryness, it retains about seventeen per cent. of water, which may be driven off by heating it in vacuo over sulphurie acid, in a temperature of 212°. When it is exposed to heat it softens and swells, but does not melt. It emits air bubbles, blackens, and at last, when nearly reduced to charcoal, it emits a low blue flame.

It dissolves slowly but completely in water, and more rapidly in boiling than in cold water. The solution is called mucilage. It is thick, and adheres, and is often used as a paste, to give stiffness and lustre to linen. It may be kept for a great length of time without undergoing spontaneous decomposition, but it becomes at last acid.

It is insoluble in alcohol and ether. Alcohol throws it down from water, but not completely. The acids dissolve gum if they be dilute; the more powerful acids, if they be concentrated, decompose it. If the powder of gum be triturated with concentrated sulphurie acid, a combination takes place, and we obtain a slightly coloured mass, which in twenty-four hours becomes darker. If we dilute it with water and saturate the acid with chalk, we obtain the gum precisely in the state that sawings of wood assume when treated with the same acid. When sulphuric acid and gum are boiled, the gum is decomposed, sulphurous acid is given out, and a charry matter remains, weighing only r 0∙29 of the gum. It is said, that by boiling gum in dilute sulphuric acid, sugar may be formed in the Same way as by boiling starch.

When gum is heated gently in nitric acid, and then allowed to cool, mucic acid is deposited, amounting to nearly one fourth of the weight of the gum. When the digestion is continued, malic and oxalic acids are formed. Vauquelin affirms that chlorine gas converts gum into citric acid. Iodine produces no change on gum.

It combines readily with the saline bases. The solution of potash converts it first into a substance not unlike curd, and then dissolves it. Alcohol throws down the gum in white flakes, but it obstinately retains a portion of the potash, and is more brittle than when pure. Lime water, and the other alkalies and alkaline earths, likewise unite with gum, and form compounds which are soluble in water. Silicated potash, when mixed with a solution of gum, though even much diluted, occasions a flaky precipitate. An abundant precipitate falls when the solutions of gum and diacetate of lead arc mixed together. It is like curd; and after being washed and dried it remains white, and is easily reduced to powder. This compound consists of
[table]

A good many experiments have been made to determine the constituents of gum. The following little table exhibits the result of these experiments.
[table]
[7:6:478]

The atomic numbers which agree best with the analysis of Prout are,
[table]

But 19∙25, the atomic weight deduced from these numbers, does not accord with 23 ’ 2, the atomic weight deduced from the composition of gummate of lead. We must therefore consider the true atomic nronortions as
[table]

The atomic weight then is 23'25, and gum contains no fewer than thirty-seven atoms.

Such are the properties of gum-arabic. Gum-senegal is the produce of another species of acacia. It comes to us from the west coast of Africa; and, being cheaper, has almost superseded the use of gum-arabic in this country. It is darker coloured and in larger pieces; and the mucilage which it forms with water is not so adhesive and thick: in other respects it resembles gum-arabic in its properties.

2. Bassorm. — This variety of gum was first particularly described by Vauquelin under the name of bassora gum. John gave it the names of cerasin and jtmwztn; and Bucholz called it tragacanthin, because the properties of gum tragacanth are the same; while Berzelius gave it the name of vegetable mucus.

It is a solid substance, having exactly the external appearance of gum. It is usually harder than gum, and not so easily reduced to powder. In general it is nearly white; but some varieties of it are yellowish, and others reddish-brown and deep. When put into water it does not dissolve like gum, but gradually imbibes that liquid, swells up very considerably, and becomes transparent and gelatinous, but does not dissolve. It dissolves in boiling water, but again partially precipitates in a gelatinous form as the solution cools. It is insoluble in alcohol and ether. It dissolves readily in solutions of ammonia, potash, and soda, especially when assisted by heat.

Its aqueous solution is not completely precipitated by alcohol. When mixed with diacetate of lead an immediate precipitate does not fall, but in twenty-four hours it makes its appearance. It is not coagulated by sulphated peroxide of iron, as is the case with common gum; nor is it precipitated like gum by silicated potash. But with perchloride of tin it forms a coagulum, having the form of a stiff jelly. It is not precipitated by the infusion of nutgalls.

3. Gum Kuteera. — This gum is the produce of the ster-culio urens, a tree which grows in Hindustan. It is in large roundish lumps, having a brownish-red colour, much lighter than cherry-tree gum, and is not hard, but soft and elastic. When put into water it gradually imbibes that liquid, and swells into a transparent and almost colourless jelly. But none of it dissolves in that liquid. In this respect it agrees with bassorin. But if we boil the jelly for some hours, we obtain a complete solution, from which no precipitate falls when the liquid cools. The solution, even when much concentrated, possesses very little of the mucilaginous qualities which characterize the aqueous solution of gum; nor can it be employed for pasting together pieces of paper or stiffening linen. Large quantities of this gum were brought to this country about thirty years ago from India, for the use of the calico printers, but it was found not to answer. A tea-spoonful of its powder gives to water the consistence of capillaire. In India it enters into the composition of some varnishes.

4. Cherry-tree Gum.- —The prunus avium, the common cherry and plum trees, and the almond and aprico, likewise yield a gum, which exudes in abundance from natural and artificial openings in the stem. It is in large, dark, reddish-brown masses, at first soft and elastic like gum kuteera; but by keeping it becomes exceedingly hard, and breaks with a glassy fracture. When put into water it swells like bassorin into a jelly; but a portion dissolves in cold water, while the gelatinous portion does not dissolve even by several hours boiling. The portion dissolved is similar in its characters to gum kuteera. When treated with nitric acid it yields mucic acid.

5. Vegetable Mucus. — This substance exists in many plants, and seems to be nearly identical with bassorin. lt may be obtained abundantly from linseed, by simply infusing the seeds in ten times their weight of water. The mucilage obtained is similar to that of gum, but it is not adhesive. It is precipitated by alcohol in flocks, but the liquid does not become opaque and milky, like mucilage of gum-arabic when treated in the same manner. Diacetate of lead throws down a copious dense precipitate. No change is produced by infusion of nutgalls. Salep, from Caventou’s experiments, seems to contain a great deal of mucus.

6. Calendulm. — This substance may be obtained from the calendula officinalis, and was first described by Geiger in 1818. The leaves and blossoms of the calendula are digested in alcohol. The infusion is evaporated to the consistence of an extract. This extract is first treated with ether, which separates a green-coloured vegetable matter, and afterwards with water. There remains a bulky mucilaginous matter, almost insoluble in water, whether cold or boiling hot. When dried it is yellow, translucent, and brittle. In water it again swells out into a mucus. The great distinction between it and mucus is its solubility in alcohol. It is insoluble in dilute acids, but dissolves in concentrated acetic acid. The dilute solutions of caustic alkalies dissolve it, but not the alkaline carbonates, nor lime water. It is not precipitated by the infusion of nutgalls. It is insoluble in ether, and in the fixed and volatile oils.

Sect. IV.— Of Gluten and Albumen.

The gluten of wheat was first obtained by Beccaria in 1742. To procure it we have only to make, a quantity of good wheat flour into dough, and knead it between the fingers, while a small stream of water falls slowly on it. We continue the kneading as long as the water passes off milky. What remains in the hand is the gluten.

It is a gray, tenacious, ductile mass, which may be extended to twenty times its original length without breaking. It adheres very tenaciously to other bodies, and has often been employed to cement together pieces of broken porcelain. In this state it is a mixture of vegetable gluten and albumen, rarely free from some bran and a little starch. To obtain pure gluten and albumen from this matter, it must be digested in boiling alcohol till that liquid ceases to become muddy on cooling. The alcohol dissolves the gluten and leaves the albumen.^[14. The albumen thus obtained was called ŵno¶ĩe by Taddei. ]

1. Gluten. —The gluten precipitates when the alcoholic solution is mixed with water, and the alcohol is distilled off. > In the liquid which remains the gluten swims inadhesive flocks. A small portion of it is united to gum, and held involution in water. Gluten thus obtained has a [7:6:479] light-yellow colour; and when the liquid is stirred it collects altogether into an adhesive mass, which sticks to the fingers, is elastic, and recovers its form after being forcibly drawn out. It is destitute of taste, but has a peculiar smell. When left to itself in a dry place, it assumes a darker yellow colour, and dries into a translucent brittle matter, resembling a dried animal substance. It dissolves in alcohol with a light-yellow colour; and if the solution be evaporated, the gluten remains in the state of a yellow translucent varnish. When cold alcohol is poured on gluten, it becomes white, a glutinous matter separates in plates, and the liquid becomes milky. The substance which thus separates is not gluten, though its properties approach those of that substance. Boiling alcohol takes it up, but when a concentrated solution cools it becomes glutinous.

If gluten be dissolved in boiling spirits, it is deposited, on cooling, with the whole of its glutinous characters. It is insoluble in ether, and in fixed and volatile oils. When steeped moist in acetic acid it swells out, becomes adhesive, loses its yellow colour, and assumes a half-liquid appearance. If in this state it be mixed with water, glutinous flocks remain undissolved, and the liquid has the appearance of water mixed with some drops of milk. Boiling does not alter the appearance of this liquid. In this case the gluten dissolves in the acid; but the other substance with which it is mixed, which is difficultly soluble in alcohol, is insoluble in the acid, becomes glutinous, and separating from the liquid very slowly, occasions its milky appearance.

The solution of the gluten in acetic acid, freed as much as possible from the glutinous substance, which is insoluble in the acid, dries to á colourless translucent varnish. When caustic ammonia or its carbonate is added in such quantity as not to saturate the acid completely, it falls down in flocks, which in about an hour collect together, and assume the usual appearance of vegetable gluten. In this state, when treated with warm water, a small portion of it dissolves, for the liquid is slightly precipitated by infusion of nutgalls.

When gluten is covered with a dilute organic acid, and agitated in it, no solution takes place; but the gluten combines with a portion of the acid. If wq now pour off the dilute acid and digest the gluten a couple of times in water, the gluten dissolves; but the peculiar glutinous substance already mentioned remains.

The compound of gluten and sulphuric acid is very difficultly soluble in pure water, but it dissolves very readily in nitric or muriatic acid. It is soluble also in boiling alcohol; and if a little carbonate of lime be added to the boiling hot liquid, the gluten may be obtained from the alcohol afterwards, quite free from acid.

When dilute caustic potash is mixed with gluten in water, it becomes slimy, and dissolves the gluten into a muddy liquid, which cannot be made transparent by filtering. When more gluten is added than the alkali can dissolve, so as to saturate the potash, the liquid loses its alkaline taste, but acquires an astringent flavour, and is almost colourless. When evaporated at a temperature not exceeding 100°, a portion of the dissolved matter precipitates, and then dries into a white opaque mass, which twists itself up, and does not adhere to the vessel. When water is poured upon this substance, the gluten dissolves, while the other matter remains in the form of a slime.

Ammonia, even when concentrated, has little dissolving power on gluten in its solid state; but when a solution of’ it in an acid is dropt into caustic ammonia, the precipitated gluten is almost immediately re-dissolved. Lime water acts in the same way.

The compounds of gluten with the other bases are all insoluble in water, and precipitate when glutinate of potash in a neutral state is mixed with an earthy or metallic salt. These precipitates have the usual colour which characterizes the salts of the bases employed.

Gluten is not dissolved by the alkaline carbonates, which throw it down from its solution in acids the more completely the more of the precipitant we add, and the more concentrated the solution is. If the alkaline liquid be poured off, the precipitate may be dissolved in pure water, constituting a muddy liquid.

The solutions of gluten are precipitated white by corrosive sublimate. The solution of gluten in acetic acid is not precipitated by acetate or diacetate of lead, nor by sulphated peroxide of iron; but it is readily precipitated by infusion of nutgalls.

2. Albumen. — The albumen remains undissolved when Beccaria’s gluten is boiled in alcohol. It is considerably reduced in volume, has lost all its glutinous characters, and is easily dried into a white or gray hard mass. When digested in a very dilute alkaline ley, it swells and becomes moist, and then dissolves into a clear colourless liquid, leaving the bran and the starch with which it had been mixed. If the alkaline solution be saturated, and quite free from carbonate, it has no alkaline taste whatever; and when evaporated, it lets fall at first a little coagulated albumen, and then leaves a white mass, which is attached to the glass, and which is again soluble in water, with the exception of the portion which had coagulated during the evaporation. By mixing this saturated alkaline solution of albumen with the different earthy and metallic salts, we may obtain combinations of albumen with the other bases. These compounds are generally insoluble in water. The albuminate of peroxide of iron is dark red after being dried; that of protoxide white, but it becomes yellow when exposed to the air. The albuminate of copper is bluish-green, the albuminates of mercury and lead snow-white.

Albumen is soluble in water before coagulation; but it is insoluble in alcohol, and it is coagulated by the action of that liquid. When dried it becomes white, gray, brown, or black. It dissolves easily in caustic alkali, and neutralizes the taste. From this solution it is precipitated by acids, provided they be added in excess. Such an excess of acid as gives a perceptibly sour taste, and causes the liquid to redden vegetable blues, may be added without occasioning any precipitation. The liquid becomes merely milky, and recovers its transparency when heated. When a considerable excess of acid is added, the albumen is thrown down, and the precipitate is a compound of the albumen and the precipitating acid, scarcely soluble in acidulated water, but easily soluble in pure water.

One of the most remarkable characters of albumen is, that itfe combination with an acid, if in solution in water, is precipitated white by prussiate of potash.

Einhof, to whom we are indebted for the establishment of most of the preceding facts, examined also the gluten and albumen of rye, oats, and peas, and showed that they possessed various peculiarities, which he minutely details. For these investigations the reader is referred to the different volumes of Gehlen’s Journal, where Einhof’s papers originally appeared.

Sect. V.— Of Lignin.

What is at present called lignin by chemists, is the peculiar substance of trees called wood, after it has been deprived of all foreign matter. It is very different in different trees, in its colour, hardness, specific gravity, &c. It probably also differs in its constitution, though this has not been ascertained by experiment. Its texture is always porous, inconsequence of the numerous vessels which [7:6:480] pervade it. In 100 parts of dried wood there exists about ninety-six parts of lignin and four parts of foreign matter, which may be removed by digestion in water and alcohol.

To obtain pure lignin, the method followed is to take a portion of wood, or rather of saw-dust, and to digest it first in water, then in alcohol, and successively in ether, muriatic acid, dilute potash ley, and even in chlorine, so long as these menstrua continue to dissolve anything.

It is white, opaque, and of a fibrous texture, and these fibres have different directions in different species of trees. Its specific gravity varies, as is evident from the following little table.
[table]

Lignin is destitute of taste and smell, and is of course insoluble in all the menstrua employed in purifying it.

When heated it becomes brown, and gives out moisture. When heated during four days in an oven, it was charred, and gave out a bituminous matter, insoluble in water and alcohol, but soluble in ether, though with difficulty. By this treatment it was deprived of more than half its weight. When distilled in a retort it becomes black, without melting, softening, or altering its shape. It gives out carbonic acid and carburetted hydrogen gas, water, acetic acid, pyroxylic spirit, empyreumatic oil, and resin.

Nitric acid gradually acts upon lignin, transforming it into a kind of starch, while malic acid is evolved. By long continued boiling the lignin is dissolved, and a quantity of oxalic acid formed.

Lignin heated in concentrated sulphuric acid is charred, and the residual charcoal amounts to 0∙4375 of the original weight of the lignin. If it be boiled with dilute sulphuric acid, it is converted first into gum, and afterwards into sugar, while at the same time a peculiar acid is evolved. When mixed with potash ley, and pretty strongly heated, it is converted into oxalic acid.

A good many experiments have been made to deter· mine the composition of lignin from various kinds of wood. The following little table shows the results of these analyses.
[table]

If we take Dr Prout’s analysis of boxwood dried at 350°, we Arid that it gives the following as the ratios of the atoms which enter into the composition of lignin:
[table]

The analysis of the same lignin dried at the ordinary temperature of the air gives us
[table]

We see from this that the heat merely drives off a quantity of water, without altering the carbon. This will be better seen if we state the atomie constitution of lignin in different states of dryness as follows:
[table]

Wċ perceive that by the heat two and a half atoms of water i have been driven off. Being ignorant of any definite compound into which lignin enters, these analyses do not enable us to determine its atomic weight.

The following Vegetable principles seem to be so closely connected with lignin that they can scarcely be considered as constituting distinct genera. We shall therefore r hbtice them here.

2. f iïîëdullm. — This is a name by which John has distinguished the pith of the sun-flower (helianthus annuus), syringa vulgaris, &c. It possesses the following characters:

1. It is insoluble in water, alcohol, ether, and oils.

2/ It is destitute of taste and smell.

3. Its Structuré is peculiar, being full of pores.

4. It is soluble in nitric acid, and when treated with a sufficient quantity of that acid it yields oxalic acid.

5. When distilled it yields a considerable quantity of ammonia, and leaves a charcoal having a metallic appearance, and a colour similar to bronze.

All these characters, except the last, so far as they arc chemical, apply to lignin as well as medullin. The last character shows that medullin contains azote as a constituent. It must, therefore, differ essentially from lignin, though, so far as it has been examined, there is a great similarity between them.

3. Suberin. — Cork, the outer bark of the quercus suber, has been examined by various chemists; but the most elaborate examination is that of Chevreul. He treated it with water in his silver digester till that liquid was capable of dissolving nothing more. He obtained an aromatic principle and a little acetic acid, which passed over into the receiver. The extract formed by the water contained two colouring matters, the one yellow, the other red; an acid, the nature of which was not determined; gallic acid, ůn astringent substance; a substance containing azote; a substance soluble in water, and insoluble in alcohol; gallate of iron, lime, and traces of magnesia. Twenty parts of cork thus treated left 1745 parts of insoluble matter.

This undissolved matter being treated a sufficient number of times with alcohol in the same digester, yielded resin, oil, and cerin, or a species of wax. The twenty parts by this treatment were reduced to fourteen parts; they were considered as pure suberin.

The properties of suberin have been imperfectly examined. It is insoluble in all the re-agents hitherto tried, except the strong mineral acids. Sulphuric acid readily chars it. Nitric acid gives it a yellow colour, corrodes, dissolves, and decomposes it, suberic acid being formed, and a peculiar dark-coloured variety of wax.

There is some reason for suspecting that the chemical [7:6:481] characters of the epidermis of most plants are nearly the same as those of suberin; but the subject has not been sufficiently investigated.

4. Fungin. — This name was applied by Bracpnnot to the fleshy part of different mushrooms after every thing soluble has been removed. He obtained it from the agaricus volvacius, piperatus, and stypticus; the boletus juglandis and pscudo-igniarius; the phallus impudicus; the merulius cantharellus, hydrium repandum and hybridum; the mucor scepticus, &c.

The mushroom is subjected to pressure, to drive out every thing liquid. The residue is treated first with water, then with alcohol, and finally with a dilute solution of potash. What remains undissolved is the fungin.

It is a white, fibrous, soft, insipid substance, possessing but little elasticity, and dividing easily between the teeth. It is insoluble in water, alcohol, ether, oils, and diluted acids. When put into the infusion of nutgalls it absorbs the greater part of the tannin contained in the liquid, and assumes a fawn colour.

Alkalies have but little action on it; yet when boiled in a concentrated alkaline ley, fungin is partly dissolved, and a saponaceous liquidis obtained, from which the acids throw down a flocky matter. Ammonia also dissolves a little of it.

Concentrated sulphuric acid chars it, acetic and sulphurous acids being evolved. Muriatic acid acts on it very slowly, converting it into a jelly which is soluble in water. Dilute nitric acid disengages azote from it. When distilled with six times its weight of nitric acid, it becomes yellow, swells up, and effervesces; but the violent action is soon over. Hydrocyanic acid is evolved, and oxalic acid formed, together with two fatty bodies resembling tallow and wax. When mixed with water, and left to spontaneous decomposition, it emits at first the smell of putrid cheese; but this smell soon goes off', and the putrefactive process stops, or goes on very slowly.

These characters show that fungin, though resembling lignin in many of its characters, yet differs from it in others; and that it contains azote as one of its constituents. In this respect it agrees with medullin, though it differs from that principle in others of its characters.

5. Pollen'm. — This name was given by Dr John to a substance found in the pollen of the pinus abies, pinus sylvestris, and lycopodium clavatum, and supposed by him to constitute a characteristic constituent in every pollen. •It was first recognised by Bucholz in 1806, in the pollen of the lycopodium. Fourcroy and Vauquelin showed it to exist also in the pollen of the phoenix dactilifera.

Pollenin is yellow, and destitute of taste and smell. It is insoluble in water, alcohol, ether, fixed and volatile oils, and naphtha. It is insoluble also in alkaline leys. It appears to be soluble in muriatic acid, and to be precipitated by ammonia. When distilled it yields ammonia, showing that, like medullin and fungin, it contains azote as a constituent.

It is exceedingly combustible, burning with a kind of explosion. It is well known that the pollen of the lycopodium clavatum is used on the stage to imitate flashes of lightning, by throwing it through the flame of a candle.

Sect. VI.— Of Tannin.

The term tannin xvsls first applied by Seguin to the vegetable principle which possesses the property of converting the skins of animals into leather by combining with them. It exists in all those vegetable bodies which are distinguished by their astringent taste. There are doubtless various species of it, distinguished from each other by their properties; but the tannin from oak bark and from nutgalls, a concretion which appears upon different species of oak, but the best of which are brought to this country from the Levant, is considered as constituting the purest kind of it. We shall therefore, in the first place, describe the characters of tannin from nutgalls.

1. Tannin from Nutgalls. — Nutgalls are excrescences of the oak (quercus robur), occasioned by a small insect called cynips querci folii, which deposits an egg in the substance of the leaf, by making a small perforation through the under surface. The ball presently begins to grow, and the egg in the centre changes to a worm; the worm gradually changes into the perfect insect, which, by eating its way out, leaves a round hole. The best galls come from Aleppo; they are bluish, and dark on the surface, hard and thick. Two of them are considered equivalent to three of the galls from the south of Europe. Their taste is exceedingly astringent. They contain gallic acid and tannin, and a considerable quantity of lignin. Sir H. Davy endeavoured to show that, besides these substances, there exists also a considerable quantity of extractive matter. But his reasons for that opinion are far from satisfactory; and nobody has been able to obtain any such extractive matter from nutgalls in a separate state. To obtain pure tannin from nutgalls, we may adopt the following process:

Reduce the nutgalls to small pieces, but not to powder, and digest them for two or three days in a sufficient quantity of water. A dark-brown infusion is obtained, which must be strained through a cloth, to separate the insoluble portion of the galls. Saturate this infusion nearly, but not completely, with caustic ammonia, taking care that it still possesses decided acid characters. Now add a solution of chloride of barium as long as any precipitate falls. Leave the liquid to become clear in a bottle well corked and filled with the mixture; for when left in the open air, gallate of barytes precipitates green. Decant oft' the clear liquid from the tannate of barytes, and wash that residue on the filter with cold water, taking care not to employ too much of that liquid, as the precipitate is somewhat soluble in water. It is now to be dissolved in acetic acid, which will leave a little green gallate of barytes (proceeding from the action of the air on the liquid) undissolved. Filter the solution, and mix it with acetate of lead. Ą yellowish precipitate falls, which, when washed, becomes grayish green. This compound is decomposed while still moist, by a current of sulphuretted hydrogen gas. The lead is thrown down, and a solution of pure tannin is obtained, which by cautious evaporation leaves the tannin in a state of purity. . ·. ∙

While in solution in water it is nearly colourless, but it becomes yellow when obtained in a dry state. It has no smell, but a purely and intensely astringent taste, and strongly reddens litmus paper. It does not imbibe moisture from the atmosphere, and is very easily reduced to powder. When heated on platinum foil it decrepitates, softens, swells, chars, and burns with a bright flame, leaving a charcoal which is easily consumed by continuing the heat. . l

When distilled it gives off, in the first place, a thick smoke and inflammable gas, which is followed by a yellowish oil, and by a liquid which on cooling deposits colourless crystals. These crystals seem, at first sight, to consist chiefly of gallic acid; but they do not strike a black with the salts of peroxide of iron, but give them a yellowish-green colour, while a precipitate falls having a grayish-green colour. Very little ammonia is found among the products of distillation.

Tannin dissolves easily both in water and alcohol. Absolute alcohol, however, does not dissolve it without the assistance of heat. It dissolves also in ether of the spcci-fìc[7:6:482] gravity 0∙72. The ethereal solution is colourless, and after spontaneous evaporation the tannin is left very nearly colourless and translucent. When the tannin is now digested in ether, there usually remains undissolved a yellowish-brown portion, which does not dissolve in ether, and which even water does not take up completely. Tannin is insoluble ip oils, both fixed and volatile.

When a solution of tannin in water is left to the influence of the air, it becomes gradually darker coloured; and if it be evaporated to an extract, it hardens to a brittle mass, which, when digested in water, leaves a brown sub-stance undissoļved. We s ’ ceherd a gradual decomposition of the tannin, the insoluble portion being kept in solution by the unaltered tannin. It is in this altered state that tannin exists in the infusion of nutgalls and of oak bark. When this altered tannin is precipitated by a lead salt, and the tannate of lead is decomposed by sulphuretted hydrogen, only the pure unaltered tannin is dissolved by the water, while the altered tannin remains mixed with the sulphuret of lead. It may be partially removed from this sulphųret by boiling water, and still better by ammonia, which forms with it a dark-brown liquid. This liquid bcing evaporated, leaves a dark-brown substance, almost destitµte of taste, and which does not precipitate lime water unless an acid be added, when a brown coagulum is formed, (Containing lime. ,

A solution of tannin mixed with chlorine water becomes brown aryl muddy, and undergoes an alteration similar to what takes place when it is left to evaporate spontaneously in the open air.

With acids tannin unites readily, and most eagerly of all with sulphuric acid. When this acid is put into’the infusion of nutgalls, it forms two different combinations. What falls first is agglutinated together, and when stirred becomes glutinous, and finally translucent and yellowish brown. When agitated in cold water it dissolves in small quantity, but the liquid acquires a yellow colour and an astringent taste. After being repeatedly treated with cold water, a light-gray powder remains undissolved. In boiling-hot water it dissolves with a dark-brown colour, and the liquid becomes muddy on cooling. A brown powder precipitates, leaving the solution of a lighter colour, but retaining a quantity of sulphated tannin. It is readily soluble in' alcohol, with a dark-yellow colour, leaving a small residue of powder.

Nitric acid occasions a precipitate when poured into a solution of tannin; but an excess of the acid speedily diminishes the precipitate, while nitrous gas is evolved, and the solution becomes yellow. When caustic ammonia is added to,the liquid, a precipitate falls, at first reddish, then grayish-grecn, and finally brown. A sufficient quantity of nitric acid evolves malic and oxalic acids. Tannin is precipitated more completely by muriatic, phosphoric, arsenic, oxalic, tartaric, and malic acids. A little boracic acid may be dissolved by the solution of tannin when assisted by heat. On cooling, the whole liquid assumes the form of a jelly, ŵhich, after being dried, is a bulky snow-white.'substance, soft to the touch, like the finest talc. Tarihin is not precipitated by acetic acid. All these precipitates are combinations of tannin with the precipitating acid. They are insoluble in an excess of the acid, but soluble in pure water. When acids are dropt into the infusion of nutgalls two precipitates fall. The first, which contains the dark-coloured and altered tannin, is difficultly soluble in water; but the other, containing the unaltered tannin, dissolves easily.

Tannín exhibits a marked affinity for the saline bases. With potash it,forms a white pulverulent compound, difficultly soluble in water. It precipiíates when a strong solution of tannin is mixed with hydrate of potash, with carbonate or with bicarbonate of potash. If the tannin was pure, the tannate of potash is formed. The compound is white and earthy looking, and undergoes no change when exposed to the air. When dissolved in the smallest quantity of boiling water it forms a yellow liquid, which on cooling assumes the form of a gelatinous mass, and after spontaneous drying, it recovers its original earthy appearance. If it be dissolved in a large quantity of water, it remains in solution after cooling. This solution has neither an alkaline taste, nor does it re-act as an alkali. Its taste is simply astringent. It constitutes a neutral salt, which maybe distinguished by the name of tannate of potash. When it is mixed with lime water no precipitate falls till the potash be saturated with an acid. An excess of potash causes this salt to dissolve in water. The solution is yellow; but if too great a quantity of potash be added, the tannate falls down if the liquid be left to spontaneous evaporation.

Tannin gives with soda a much more soluble salt. It does not fall unless the solutions be very concentrate, and even then but imperfectly. When the compound is as nearly neutral as possible, and left to spontaneous evaporation, it gives a greenish-yellow half crystallized mass. Cold water dissolves a portion of this matter, and leaves a matter which remains undissolved, like tannate of potash. This being dissolved in boiling water, and left to spontaneous evaporation, a white powder falls, which is quite neutral. The crystallized portion, soluble in cold water, is insoluble in alcohol. It contains ån excess of alkali.

With ammonia tannin combines, exhibiting similar phenomena as with potash. Tannate of barytes is very little soluble in cold water. It precipitates white when tannate of potash or ammonia is mixed with chloride of barium. Hot water dissolves it in considerable quantity. Tannate of strontian is similar to that of barytes. When hydrate of lime is added in excess to a solution of tannin, almost the whole is thrown down, and a subsalt formed; but neutral tannate of lime is soluble in water, and the liquid assumes a yellow colour. The dry salt is yellowish brown, and translucent, and soluble both in water and spirits.

When a solution of tannin is digested with hydrate of magnesia, or with magnesia alba, the earth acquires a yellow colour, and a subsalt is formed, almost all the tannin being removed from the liquid. When the infusion of nutgalls is employed, the liquid becomes green from the gallate of magnesia.

Tannin combines with the metallic oxides, and forms difficultly soluble compounds. These salts may be obtained by mixing tannate of potash dissolved in water with a solution of the metalline salts. Indeed several of the metallic salts are precipitated by the solution of tannin in water, viz. the salts of lead, copper, protoxide of tin, silver, mercury, peroxide of uranium, protoxide of chromium, &c. The colour of most of these précipitâtes is similar to that which infusion of nutgalls strikes with the same salts.

With protoxide of iron tannin gives no precipitate. When mixed with it in a very concentrated state, a white gelatinous magma is formed, which, when diluted, dissolves. With the peroxide of iron tannin forms a black compound, which is the colouring matter in our common ink.

With the protoxide of lead tannin unites in various proportions. When a solution of tannin is mixed with acetate of lead, a white precipitate falls, which darkens when exposed to the air. It must therefore, if we wish to preserve its white colour, be dried in vacuo, over sulphuric acid. This precipitate contains an excess of tannin. If it be boiled in water the excess of tannin is dissolved, and a ndutral tannate remains, which water is incapable of decomposing. If it be digested in caustić ammonia, it becomes mucilaginous and dark' coloured, but is not otherwise[7:6:483] altered in its nature, This neutral tannate is a compound of
[table]

We obtain a subtapnate when√we mix a solution of·tannin with diacetate of lead. The precipitate is white, but when washed it becomes yellowish, with a shade of greep.

When a solution of tannin is mixed with tartar-gmetic dissolved in water, the oxide of antimony is precipitated in combination with a portion of the tannin, while at the same time another portion of the tannin replaces the oxide of antimony in the tartar-emetic. √ The consequence is, that no cream of tartar appears, but a salt is formed similar to the combination of cream of tartar with boracic acid. ... ,; -, . . ,

Tannin combines with all the vegetable bases described in the last chapter, and forms with them very little soluble compounds, which in general are distinguished by a white colour. They may be separated from many other precipitates which tannin forms with vegetable bpdies, in consequence of the property which they have of being soluble in alcohol. These tannates may be freed from tan-nin if an alcoholic solution of them be dropt into an aqueous solution of acetate pf lead. The oxide of lead precipitates in combination with tannin,, while the vegetable alkaline base remains in solution combined with acetic acid. Several of the salts have the property of precipitating tannin from its solution. Sulphate, nitrate,, and acetate of potash, occasion a precipitate when dropt into tannate of potash, but the precipitate consists chiefly of tannate of potash, i .Common salt acts in the same way.

Tannin occasions precipitates when dropt into solutions of starch, albumen, and gluten. It combines with many animal substances.

The affinities of tannin, when it acts as an acid, are feeble. ∙> i

Berzelius analysed it by consuming tannate of lead by means of chlorate of ootash. He obtained the following for its constituents
[table]

The number of atoms corresponding best with this analysis, and with the atomic weight deduced from the composition of tannate of lead, is the following:
[table]

Besides the tannin frpm the oak and from nutgalls, whiqh is considered as the purest, there are various other varieties which have not hitherto been examined sufficiently in detail. Thus the tannin in the bark of the cinchona officinalis strikes a green colour with salts of peroxide of iron. The tannin in catechu, a substance t which comes from India, and is extracted from the mimosa catechu, also throws down ∣ the persalts of irpn green. Catechu, which is an extract from the coccoloba uvifera, contains also a tannin which strikes a green with the same salts.

Sect. ∖ r ll^-Of Vegetable Colouring Matter. ’ > ' . φ . 1 Γ<< f

That many substances exist in plants capable of communicating different colours to other bodies, is. sufficiently known. In this section we, shall tpke a qursory view 1 of some of the most important of these bodies. To write a

- complete account of them all would be to introduce into tfie article CnßMĮSŢftYg treatise pn dyeing f , ' ,- 1 .

The most common vegetable colours are rod, yellow, green, and blue. , , r ,.∙ .. ι , n y rr, ‘ , t j, . 1 √X

,r 1. Tied Colouring Matters. v n ra ’ ∙ da' ’ ' ’ n*

The most important of the red colouring mat 1 ters of vo: getables is madder, the root of the rubia tinctorum, a plant which is cultivated as a dye-stuff in Turkey áŕňįl the Le- ; vant. It is raised also in Hollandbut the Dutch)ma<⅜- . der, owing to the coldness of thq climate, is not pearly sp ; rich in colouring matter as tķat frodţ Turkey. When these . roots are employed in dyeing/they areyn the first þlapp: cut, into a kind of powder by stumpers driven by machinery.

When madder roots are 1 digested in cold water, gu⅛1, sugar, yellow extract, r and maliċ aĉĩd, are dissolved·, T⅛0 liquid is poured off, and the maceration repeated as ļòĥg as these substances are, taken up. The roots thus purified arc ,boiled in water, Which dissolves a considerable quantity of the red colouring 1 matte‰ especially if a little carbonate of soda be, dissolved in the liquid· Filter t⅛e deep-red decoction, and mix it with sulphuric acid. The colouring matter is* thrown down of a yellow ċolour in combination with the acid, t Collect the precipitate, on the filter, and wash it with, dilute sulphuric acid., Subject it to pressure between folds of filtering, paper, and then dissolve it in alcohol of the specific gravity 0∙83, which will leave undissplved a small quantity of foreign matter. The filtered red liquid is apid. If it be mixed with cär- * bonate of potash in small quantities at a time till the acid be saturated, and the liquid be separated from the sulphate of potash, precipitated, and then evaporated to dryfiess,.a red imperfectly crystallized matter remains, which constitutes the colouring matter ,of madder, or rubin as jt might be called. ..When prepared in this way, which'is the process of Kuhlmanq, it may. not be free from alkali. ,

It is soluble in cold water; but the solution is very easiļy altered Ay the action of the air, so that while, we are evaporating the solution, a good deal of,the rubin falls in an insoluble state, f Tlp s propensity js so strong, that madder ,rpots are injured By free .exposure, to the air. Rubin is soluble in alcohol,,and the solution keeps moderately well, yet at last it,becomes muddy, and ìetsfall brown flocks. The aqueous solution is thrown down yellow by acids, but the alcoholic is merely rendered yellow without any prqcipitation. Ţhe alkalies combine with rubin without altering its colour. The compound which it forms with barytes is reddish brown, that with strontian kermes red. Iţ is dissolved j>y lime water and chloride of calcium without any precipitate falling. The compounds which it forms with the earths proper are red. It combines with the metallic oxides. With protpcìilorifle of tin it gives a reddish-yellow colour, with acetate of lead a dark-reddish brown, with,,nitrate of mercury a Ţne amethyst-red, with nitrate of silver a smµ tty-reddish brown, and .with acetate of iron a dark brown. , .∩ 1 ,, < ι. . t '√.

Rubin has a,strong affinity for different animal substances. It dissolves in, i albumen wheμ diluted with wafer. When the albumen is t coagulated by heat, the colouring matter unites with the cpagulurn, and the liquid only,retains a yellow, colour. Urine dissolves rufijn from madder .root. Milk acquires.a yellôvy eplpur, apd.deposits a red-coloured curd. It does not precipitate, the splutiòņ of gļue.

It is well known that rubin constitutes the cqlouring .matter of the Turkey-red dye, whiph is the most beautiful and permanent red colour that,can be given to cottpn. The process is i very .compjex, and the theory of some of ⅛e steps .is t still ŗatheŗ obscµre. υ ζ l’q,.. ι.,,⅛ 7 ∕

1. Colouring Matterg; liefl Sfiundxrs.— Thi^ mattpr įs obtained from the wood pf the ptèrocarpus santalmus, a very [7:6:484] hard species of wood, from a tree which grows in the mountainous parts of India. This colouring matter is insoluble in water, but it is easily extracted by alcohol, after the evaporation of which it remains under the form of a red resin, which melts at 212°. It may be obtained also by digesting the wood in a dilute solution of caustic ammonia. The colouring matter may be thrown down by saturating the ammonia with muriatic acid., This colouring matter is easily destroyed both by sulphuric acid and nitric acid. It is readily soluble in acetic acid,· and the saturated solution is precipitated by the addition of water. When the alcoholic solution is mixed with protochloride of tin, a fine purple precipitate falls. With salts of lead the precipitate is violet. Green sulphate of iron is thrown down dark violet, corrosive sublimate scarlet red, and nitrate of silver reddish brown. From all these precipitates alcohol separates a portion of the colouring matter.

A saturated solution of red saunders in alcohol is dark red or brown, but when much diluted it becomes yellow. Ether dissolves red saunders more easily than alcohol, and acquires first a yellow, then a red, and finally a brown colour. Water precipitates almost all the colouring matter from the alcoholic solutions, but does not alter the ethereal solution. Oil of lavender dissolves four per cent, and oil of rosemary somewhat less, of the colouring matter. Oil of turpentine does not dissolve it cold, but when heated takes up one and a third per cent. of it. Fat oils are slightly coloured by it. Red saunders is employed by apothecaries to colour tinetures.

2. Colouring Matter of Brazil Wood. — This colouring matter, called Ecrnambouc∙by the French, and Birzil in Scotland, both from the parts of South America from which it is usually imported, is obtained from the wood of various species of Caesalpinia, particularly the echinata and sapan, trees which grow in South America and in India. It contains a very delicate and easily altered red colouring matter, which is rendered yellow by acids and violet by alkalies. This colouring matter may be obtained pure by the following process:

The wood is rasped down, and then treated with water. The solution which contains uncombined acetic acid is evaporated to dryness, and when the acid is dissipated it is redissolved in water, and agitated with oxide of lead in order to get rid of another free and not volatile acid. It is then evaporated to dryness a second time, dissolved in alcohol, filtered, and concentrated. It is next mixed with water, and a solution of glue is added so long as tannin continues to be precipitated. It is afterwards filtered, evaporated to dryness, and redissolved in alcohol to get rid of any excess of glue that may have been added. Finally, it is filtered and evaporated to dryness. In this state it is the pure colouring matter.

It is soluble in water and alcohol, and the solutions never exhibit their fine red colour till all acid which they may contain is neutralized. Aeids render it yellow. Sulphuric, nitric, and muriatic acids give a dirty yellow. With fluoric acid it becomes first yellow, and then greenish gray. Phosphoric and citric acids give it a very fine yellow, which may be fixed on woollen and silk. Sulphurous acid, sulphohydrogen, and boracic acid, blacken and destroy the colour. The alkalies added in slight excess change the colour to violet or blue; hence the infusion of Brazil wood is a delicate re-agent for alkalies.

3. Colouring Matter of Logwood. — This colouring matter is obtained from the wood of the Haematoxylon Campeehianum, a tree which grows in America, particularly round the Bay of Campeachy. This colouring matter has a considerable resemblance to that of Brazil wood. It may be obtained from logwood by the following process:

Digest the raspings of logwood in water of the temperature of about 125°, evaporate the solution to dryness in a gentle heat, and treat the residue with alcohol of the specific gravity of 0∙843. The colouring matter is dissolved, but a brown residue remains, which, however, is not quite free from colouring matter. Filter the solution, and distil off the alcohol, till it is reduced to the state of a thin syrup. Mix this with a little water, and leave it to spontaneous evaporation. A number of small crystals are deposited. Decant off the mother ley, and wash these crystals with a little alcohol. These crystals constitute the colouring matter of logwood to which Chevreul has given the name of hematin.

Hematin has considerable lustre, and exhibits a play of colours, varying from rose-red to yellow. When reduced to powder the colour is yellow. The taste is slightly astringent, bitter, and acrid.

Boiling water dissolves it with facility, and acquires an orange-red colour, which becomes yellow when the liquid cools; but heat again restores the original colour. When this liquid is evaporated the hematin crystallizes. The addition of an acid renders it first yellow and then red. Sulphurous acid, however, gradually destroys the colouring matter if it be left long enough in contact with it. Potash, soda, and ammonia give it a purplish-red colour, and with a considerable excess of these alkalies the colour becomes violet blue, then reddish brown, and finally yellowish brown. By this action the hematin is destroyed, for the colour cannot be again restored. Barytes, strontian, and lime water produce the same effect; but they gradually precipitate hematin from its solution.

When a current of sulphohydrogen gas is passed through an aqueous solution of hematin, it assumes a yellow colour, which disappears in the course of a few days. The oxides of lead, tin, iron, copper, nickel, zinc, antimony, and bismuth, unite with hematin, and give it a blue colour with a shade of violet. Peroxide of tin acts on it as the mineral acids do. Glue throws it down in reddish flocks.

4. Colouring Matter of Lichens. — What the French call orseille is a preparation from the lichen roceella, and probably from other species. The lichen is reduced to powder, and mixed with putrid urine, or still better with ammonia distilled from it. By this process the whole is converted into reddish-blue matter, which is employed in dyeing red. What is called in this country cudbear is prepared by a similar process from the lichen tartareus. The manufacture began in Leith under the firm of Messrs M‘Intosh and Cuthbert Gordon, from the last of whom, who had the management of the work, the dye-stuff was called cudbear. It was transferred to Glasgow, where it is still carried on by Charles MTntosh and Company. The ammonia employed was originally procured from urine, but now it is obtained from the liquor which conies over during the manufacture of coal gas. The process is the same as for the manufacture of orseille, but the lichen employed is different.

There is a similar dye-stuff manufactured in Germany, under the name Persio. Cudbear is a bluish-red powder, which does not readily dissolve in water. It dissolves more readily in alcohol. The solution is red. In caustic ammonia it dissolves with great readiness, and the solution is purple. When this solution is spread on paper, and the paper allowed to dry, it becomes red. The smallest portion of alkali applied to this paper renders it purple; hence .cudbear is by far the most delicate, test of alkalies which we have it in our power to apply.

In Holland there is a preparation of lichen made in small blue cakes, which is known by the name of laernus. In this country it is called litmus, and the aqueous solution of it is called by the 1Tenelι infusion of turnsole. This [7:6:485] solution is blue, but the smallest addition of an acid renders it red. It is one of the most delicate tests of acids, and is usually employed by chemists for that purpose.

Cudbear does not constitute a fast colour, though it is a beautiful one. It is chiefly used as a ground on which other colours are to be applied. Thus blue cloth is often dyed with it before the application of the indigo. Cudbear is also employed generally in the dyeing of the red cloth employed in this country for making coats to the common soldiers. There is a manufacture of cudbear also in Liverpool.

2. Yellow Colouring Matters.

These colouring matters are rather numerous, but they have scarcely drawn any of the attention of chemists; we cannot, therefore, say much respecting their chemical properties. We shall merely point out a few of them as subjects deserving to be studied by future chemists.

1. Quercitron Bark. — This is the bark of the quercus tinctoria and nigra, trees which grow in North America. It was introduced as a dye stuff* by Bancroft in 1775. It contains a yellow-colouring matter, seemingly nearly the same with what occurs in other vegetables; but when impure, it has a greater tendency to pass into brown than most other yellow dyes.

Heat seems prejudicial to this colouring matter, for the decoction does not dye a good yellow. In this respect wοαd has the superiority. The method of using it is to make an infusion of the bark in water at the temperature of80°. The bark being now removed, the liquid may be heated to 200°, and at this temperature employed for dyeing without inconvenience.

. Water dissolves the colouring matter of quercitron bark with facility, and acquires a brownish-yellow colour. If the decoction be left exposed to the air, a white precipitate falls, consisting of resinous matter. The acids render the yellow colour brighter, unless they be too much concentrated, when they destroy it altogether. The alkalies, on the other hand, deepen the shade. Alumina put into the decoction of quercitron assumes a golden-yellow colour. Oxide of tin assumes a still deeper shade of colour. If cotton previously treated with silicate of potash be put into an infusion of quercitron, it assumes a Nankin colour.

Alum thrown into the infusion of quercitron occasions a slight precipitate of a deep-yellow colour. Cloth impregnated with nitrate of alumina acquires a finer colour from quercitron than those impregnated with alum. With sulphate of lime it gives a Nankin yellow, and with muriate of lime a buff colour, which is preferable to that obtained by means of iron. With salts of iron quercitron gives olive colours. The effects of various other salts have been determined; but the colouring matter has not yet been obtained in a separate state, nor its properties determined.

2. Woad. — Woad consists of the stems and leaves of the reseda luteola, a plant which grows wild in this country. When boiled in water, it gives a yellowish-brown decoction, which, when much diluted, becomes greenish yellow. Acids render it lighter coloured, and alkalies darker, while at the same time, if they have been added in considerable quantity, a dark-yellow precipitate falls. Alum throws down a fine yellow precipitate, and so does protochloride of tin. Protosulphate of iron throws down a dark gray, and the sulphate of copper a greenish-brown precipitate.

3. Turmeric, — Turmeric is the root of the curcuma lοnga, a plant which is a native of India. It is very rich in a fine yellow-colouring matter, which, however, is fugitive, and cannot be fixed by mordants. The colouring matter is not given but readily to water, but abundantly to alcohol. Alkalies render this colouring mattér reddish brown, and dissolve a portion of it. On this account it is employed as a. re-agent for detecting the presence of alkaline bodies; but it is not very delicate. Most acids render the yellow colour of turmeric lighter, except the boracic, which renders it reddish brown, as the alkalies do. The salts of uranium, of iron, and the supersalts of tin, bismuth, and antimony, give it a brown colour. It is employed occasionally by apothecaries to give a yellow colour to their draughts. It constitutes also an ingredient in curry powder.

4. Saffron. —Saffron is composed of the stigmata of the crocus sativus, a plant which is cultivated in England. It was examined by Bouillon-la-Grange and Vogel in 1811, who extracted from it a colouring matter, to which they r gave the name of polychroite. This substance may be obtained by the following process:

Digest saffron in water, and evaporate the infusion to the consistence of honey. Digest this yellow residue in alcohol of 0∙800, filter the solution, and distil off the alcohol. The yellow matter which remains is polychroite.

Its colour is intensely yellow. When exposed to the air it absorbs moisture, and becomes a viscid liquid. It is very soluble in water and alcohol, but insoluble, or nearly so, in ether. When the aqueous solution is exposed to the direct rays of the sun, it becomes colourless, and the yellow colour cannot be restored. Sulphuric acid gives it a deep indigo-blüe colour, which becomes gradually lilac. The same change is produced by sulphuric acid on the alcoholic solution. Nitric acid causes these liquids to assume a green colour. The addition of a little water causes the colour to disappear. Sulphate of iron throws'down a dark-brown precipitate, lime water a yellow precipitate, barytes water a red precipitate. Acetate of lead has no effect, diacetate of lead throws down a yellow, and nitrate of mercury a red precipitate. Polychroite is insoluble in oils. It seems to contain no azote in its composition, if we are to judge from the products of its distillation. ’

3. Green Colouring Matters.

From the universal prevalence of a green colour in the leaves of plants, one would naturally expect a vast variety of green colouring matters in the vegetable kingdom; ÿet there is not so much as a single vegetable substance known capable of dyeing a green colour. The green colour of leaves resides usually in a kind of resinous or waxy substance, which is not soluble in water.

What is called sap green, used as a water colour, is obtained from the expressed juice of the berries of the rhamnus infectoria, which is mixed with a little alum, and evaporated to an extract. Alkalies change'this colour into yellow, and acids into red.

To dye green, the method is to give the cloth first a yellow colour, and then a blue. ’

? 31

4. Blue Colouring Matters. ·./<> ι∙i

There are various vegetables which furnish a blue colour that may be fixed on cloth; but there is one of tĥèse so superior to all the rest, that it has superseded them all, and is alone used by the dyers. That substance is indigo.

1. Indigo. — This valuable pigment was known to the ancients. It is prepared from a variety of plants; various species of indigofera, the arg l entea, disperma, and tínċto-ria, and even others; the nerium tinctorium, marsdenia tinctoria, ascleþias tingens, isatis tinctoria, &c. The plants are cut down with sickles, and laid in strata in the steeper, a large cistern containing water. Here they' ferment, and the utmost attention is required to the process. It goes on best at the temperature of 80°. The water soon becomes opaque, and aśšumes a green colour, while gases are extricatéd. When this fermentation has proceeded far [7:6:486] enough, the liquor is let into a lower cistern, called the battery. There it is agitated for fifteen or twenty minutes by means of levers moved by machinery, till the'flocculi beginning to separate gives it a curdled appearance. A quantity of lime water is now. pòurèd in, and the blue flocculi are. allowed to subside. The water is drawn off, and the pigment put to be drained in small linen bags; after which it is put into little square boxes, and allowed to dry in the shade, , i if f i , r

Indigo, as it comes to this country, is a fine, light, friable substance, of a deep-blue colour. Its texture is compact, and the tints on the,surface of the lumps vary according to the mode of preparation; being copper, violet, and blue. The,lightest indigo is considered as the best,‘but it always contains more than half its weight of foreign matter, partly earthy, but chiefly vegetable. ļ From the late experiments of Berzelius, it appears that it contains at least four different vegetable substances, which he has distinguished by the names of indigo-gluten, indigo-brown, indigo-red, and imdigĢ-blue, --∙ i , >ı, ’ t ĩ

1. Indigo-gluten is obtained when indigo in fine powder is digested with a dilute acid. A yellow solution ⅛ obtained, but the water employed to wash the undissolved indigo contains most of the gluten, as the acid compound of it is much more soluble in water than in acid. If we employ dilute sulphuric acid, we have only to saturate the acid with pulverized marble, filter, and evaporate to dryness; the indigo-gluten (almost pure) remains. ' It may be dissolved in alcohol, and the alcohol may be distilled off. The gluten remains in the form of a translucent shining varnish. It is soluble in water, and tastqs not unlike beef tea. When heated on platinum foil it melts, and burns with flame, and leaves a very small quantity of white ashes. When distilled it swells, and gives out a brown oil, and a water strongly impregnated with ammonia. Its aqueous solution is precipitated by the same substances which precipitate, gluten, namely, tannin, corrosive sublimate, prussiate of potash, acetate of lead, and sulphated peroxide of iron. These precipitates are white, or have a shade of yellow, t An excess of acid prevents the precipitate by tannin and .corrosive sublimate; but prussiate of potash does not occasion a precipitate unless an excess of acid be present. It combines readily both with acids and alkalies. Sulphuric acid dissolves it without becoming black. Nitric acid makes it yellow; a fatty matter is formed, and a quantity of oxalic acid. These properties make this substance approach to gluten; but it is distinguished from gluten by its solubility in water, and by its wanting the glutinous and adhesive qualities which distinguish gluten. From albumen it is distinguished by its solubility in alcohol, and by its not coagulating at a boiling temperature.

2. Indigo-brown constitutes a much greater proportion of common indigo than the gluten. It is occasionally united in indigo with lime, from which it may be separated by acids; occasionally it is combined with a vegetable acid. Indigo-brown is dissolved when the indigo, previously treated with a dilute acid, is mixed with a concentrated potash ley gently heated. The mass becomes immediately black, and swells up to a loose magma, in proportion as the alkali dissolves the indigo-brown. , The liquid passes with difficulty through the filter, and is very dark and opaque, unless in very thin layers. From this liquid acids throw down a blackish-brown matter in a half gelatinous state. If the alkaline liquid be mixed with sulphuric acid till it acquires a sour taste, and then filtered, indigo-brown remains in the-filter. The.dark colour is owing to indigo-blue being held in solution. It is exceedingly difficult to obtain the indigo-brown in a pure state. If the precipitate with sulphuric acid be digested with newly precipitated carbonate of barytes, the greater part of the acid is separated, but not the whole. ,The liquid being evaporated, leaves a translucent, brown varnish, which is not completely soluble in water, and the dissolved portion contains a little barytes. r - . nr , ι ∙

In this stateindigo-brown has scarcely any,taste. It does not act on re-agents either as an acid or alkali, when heated it becomes moist, swells, smokes, and gives out an animal smell. Finally, it take? fire and lęąves a bulky charcoal containing carbonate of barytes. It unites readily with acids, and the compounds formed are. very difficultly soluble in water. It combines equally readily with alkalies, and forms with them compounds easily soluble .in water. It saturates a certain portion of alkali l so completely, that it is no longer capable of restoring the blue colour to litmus paper reddened by acetic acid. If a solution of indigo-brown in potash be saturated with acetic acid so as to be rendered quite neutral, and then, after bejnġ evaporated to dryness, be treated with alcohol, the acetateof potash will be dissolved, and what, remains undissolved is a neutral combination of indigo-brown and potash, .q When dissolved in water and evaporated, it gives a black shining mass, in the form of long needles,like, prismatic crystals. ∙ ji . , ĩ, , .∙; i , ŗ ’. ll o v fi'⅛ ... ,ZiJ1ζ √- ..∣ . ∙I

The compound of indigo-brown and ammonia Has the .same appearance. It dissolves easily in water, and pretty readily in alcohol. The acid or alkaline solutions, of,indigobrown are not. thrown down by prussiate of potash, corrosive sublimate, or infusion of nutgalls; but acetate of lead and sulphated peroxide ofiron occasion precipitates, These precipitates have a dark colour, i ,, l ,,. ι j , ι ∙ , ,

It is decomposed by nitric acid; oxalic, acid is. formed, and a bitter-tasted yellow substance, which is spluble in caustic ammonia. , »,. l . , t ».

3. Indigo-red is obtained when indigq, after being treat-1 ed with an acid and with potash, is boiled in alcohol of ’ the specific gravity 0∙83. It is very difficultly soluble in alcohol, and requires the solvent to be boiling hot; and repeated portions of alcohol ought to be used in succession. The alcohol at first acquires a dark-red colour; hut iţ at last becomes light blue, showing that indigo-blue, is beginning to be taken up. ∣,The alcoholic solution is,yery deep coloured. It is not precipitated by water. If the alcohol be distilled off, a dark-brown matter .precipitates, consisting of a mixture of indigo-brown .anfi indigo-red. The liquid is dark red. Jf acetic acid be added in slight excess, the indigo-brown is dissolved, or may be mostly washed out with water. When the 'rqsidyal indigo-red is dissolved in alcohol, we obtain a fine,red solution. When the alcoholic solution is evaporated to dryness, the indigored remains in the form of a dark-brown, shining varnish.

It is insoluble in water, diluted acids, and alķaline leys. It is soluble in alcohol and ether, but only, in srpall quantity; but ether dissolves much more than alcohol. The dilute solutions have a fine red colour; the concentrated a deep brownish red. . , 1 , μ . λ √ .,. ? ., ' f . , 1 ..,,.

By concentrated sulphurjq acid iţ is dissolved with a dark-yellow colour. When the solution is diluted with water iţ, becomes yellowish re,d, and no, precipitate falls. When this dilu,te solution is digested .with woollen cjath it .becomes colourless,, and the, cloth assumes a colour intermediate between yellowish brownand red. Nitric, acid dissolves it with a fine purple jcolour, which speedily passes to yelipw. When heated rapidly in the open air it melts, fumes, ,takes, fire, and burns with a clear , flame,. emitting much smoke. When distilled in yąçqq it, gives first a small quantity,of colourless sublimate; it, then melts,.bqils, and is çharred. The sublimate consists^of colourless crystals mixed with unaltered indigo-red. , No gas is eγolved during the process. Alcohol dissolves tfie-indigo-red and [7:6:487] a portion of the crystals. What remains is colourless, and may be sublimed in vacuo. It is now snow-white, and consists of very small needles. It is insoluble in water, and destitute of taste and smell. It is soluble with difficulty both in alcohol and ether. The solution is of a yellowish-brown colour (perhaps from a mixture of indigored), and by spontaneous evaporation gives very small translucent and colourless crystals. Sulphuric acid dissolves it with difficulty, and assumes a fine lemon-yellow colour. Concentrated muriatic acid unites with it, giving it a yellow colour, and becoming itself yellow. Acetic acid dissolves a trace of it, but does not acquire any colour. Dilute nitric acid converts it into ihdigo-red. Concentrated nitric acid dissolves it with a purple colour, and decomposes it. Dilute nitric acid is a very delicate test of it, assuming a red colour when acted on by a very minute quantity of it. In alkalies it is insoluble even when assisted by a boiling heat.

4. Indigo-blue, or the true colouring constituent of indigo, remains after the indigo of commerce has been treated with alcohol, not however in a state of purity, some of the preceding substances still remaining, and likewise not unfrequently sand and gravel. To obtain the indigo pure, let it be mixed, while still wet, with twice its weight of lime which had been slaked just before mixing it with the indigo. Put this mixture into a flask capable of holding about 150 times its weight of water. Fill the flask with boiling water, and shake it well. To this add two thirds of the weight of the lime of protosulphate of iron in the state of a fine powder, or just previously dissolved in a little hot water; then cork the flask and shake it well. Let it remain a couple of days in a warm place. By degrees the mixture becomes green. The protoxide of iron, precipitated by the lime by little and little, is converted into peroxide at the expense of the indigo. The indigo thus deprived of a portion of its oxygen combines with the lime, and forms a compound soluble in water. The consequence of this is, that the liquid assumes a deep-yellow colour. Draw off the transparent liquid with a syphon, and pour hot water on the residue, to dissolve out all the compound of indigo and lime.

As soon as this yellow liquid is exposed to the air the indigo absorbs oxygen from the atmosphere, becomes insoluble, and precipitates in the state of a blue powder, which is pure indigo-blue. To prevent the foreign substances which may be present from falling with the blue powder, the best way is to pour the yellow indigo solution into water acidulated with muriatic acid. This acid keeps the foreign substances in solution, and requires a yellow colour. First wash the precipitated indigo with water till it becomes a fine blue, then collect it on the filter, and wash it clean and allow it to dry.

The colour has now a shade of purple, with somewhat of a metallic lustre almost like copper. When pulverized it becomes again a fine blue. It is destitute of smell and taste, and re-acts neither as an acid nor an alkali. When gently heated on a platinum plate it gives out a fine purple vapour. If the heat be suddenly increased, the indigo melts, boils, catches fire, and burns with a clear flame, emitting much smoke, and leaving a charcoal which burns with difficulty without leaving any residue. The purple smoke is a gaseous substance, or rather vapour. If indigo be put into a retort, and the retort, after being exhausted, be heated, it is filled with the vapour, which on cooling deposits itself in dark purple plates; but by this process a considerable portion of the indigo is destroyed.

Indigo is insoluble in water. Boiling alcohol assumes a blue colour when digested on it, but generally loses its colour in a few hours, while a little indigo is precipitated. It is insoluble in ether. Oil of turpentine, when boiled on it, acquires a blue colour; and the fixed oils, when treated in the same way, dissolve a portion, but the indigo is gradually decomposed. The specific gravity of pure indigo is 1∙35. >

Chlorine instantly destroys it, and gives it a yellow colour. Iodine has no action on it in the wet way; but when mixed with it and heated the indigo is decomposed. It cannot be combined with sulphur or phosphorus.

All bodies having a strong affinity for oxygen, and which are placed in contact with indigo and lime, or on alkali,' at once absorb oxygen from the indigo, and bring it to a state in which it combines with the alkaline body, and becomes in that way soluble in water.

By sulphuric acid, especially the smoking variety, it is dissolved; but the nature of the indigo is altered by the action of the acid. By nitric acid it is decomposed with a strong effervescence, and either carbazotic acid or indigotic acid maybe obtained, according to the way in which the acid is applied.

Indigo has been subjected to a careful analysis by various chemists, by means of black oxide of copper. The following little table exhibits the results of these analyses.
[table]

If we take Mr Crum’s experiment as nearest the truth, and it was made with great care with sublimed indigo, we have the following atomic ratios for the constitution of this substance:
[table]

This shows us that its atomic weight is 16∙25, or a multiple of that quantity. As we do not know any definite compounds into which it enters, we have no means of determining at present what its atomic weight really is.

Indigo rendered soluble in alkalies, by being deprived of oxygen, is known by the name of reduced indigo. It will be proper to describe its properties when in that state.

To prepare it, fill a flask with the yellow solution of reduced indigo and lime, from the indigo vat prepared by i the process formerly described. Then let fall into it a few drops of concentrated sulphuric acid or acetic acid, previously deprived of air by boiling, or by being kept in the vacuum of an air-pump. The flask must now be well corked, and care taken that not a particle of air remains in it. The acid occasions an abundant white, flocky precipitate, which is reduced indigo. The purer the solution is, the more difficultly does the precipitate fall to the bottom. When the matter has been left twenty-four hours to collect at the bottom of the vessel, collect the precipitate on the filter, and wash it with water which has been long boiled and allowed to cool in a well-stoppered -bottle, till the uncombined acid disappears. During this washing the colour darkens, but it does not become blue, but acquires a grayish-green colour, especially on the surface. Let the washed matter be pressed between folds of blotting paper, and then dried in vacuo over sulphuric acid.

It is a grayish-white matter, having a silky lustre and some slight appearance of crystallization. It has neither taste nor smell, and produces no change on vegetable blues. It is insoluble in water. It is soluble both in alcohol[7:6:488] and ether, with a yellow colour. When the solution is exposed to the air, oxygen is absorbed, and blue indigo precipitates.

It does not combine with diluted acids. Concentrated smoking sulphuric acid dissolves it instantly with a dark purple colour. It combines very readily with the saliform bases. It dissolves both in caustic alkalies and their carbonates, and likewise in barytes, strontian, and lime, with a yellow colour. The ammoniacal solutions are generally green, in consequence of a little blue indigo which is dissolved along with the white portion. Whenever thèse solutions are exposed to the air, the indigo becomes blue and is precipitated.

Lime forms two distinct compounds with reduced indigo. The first is a saturated solution of the indigo, known only in the liquid form, and having a dark-yellow colour. The other has an excess of lime; it is insoluble, and lemonyellow in colour. It falls to the bottom in consequence of the excess of lime employed when indigo mixed with lime is reduced by means of sulphate of iron; and as it is heavy, the gypsum and peroxide of iron may be washed away. It is slightly soluble in water previously deprived of air, giving it a slight shade of yellow. When exposed to the air it becomes first green and then blue by the absorption of oxygen.

Reduced indigo even forms a soluble compound with magnesia, but it requires more water to dissolve it than the compound with lime.

The other bases may be combined with reduced indigo, by putting the salts containing them in a clear solution of reduced indigo as neutral as possible, taking care that air be excluded. Alumina forms with it a white compound, which instantly becomes blue when exposed to the air. The salts of protoxide of iron, protoxide of tin, and protoxide of lead, give white compounds with reduced indigo. Neutral sulphated peroxide of iron throws down a darkbrown compound, which does not alter under the liquid so long as all the reduced indigo is not thrown down. But if an excess of the salt be employed, that excess is changed into a protosalt, and the precipitate becomes blue. The salts of the protoxides of cobalt and manganese give green precipitates. Nitrate of silver throws down a brown, and afterwards a black precipitate, which is not altered by exposure to the air.

From the experiments that have been made upon reduced indigo, there is reason for believing that it differs from blue indigo merely by containing one atom less of oxygen. Hence its constituents must be,
[table]

It is in this state that it is combined with cloth. W r hen the cloth is exposed to the air it gradually absorbs oxygen, and becomes first green and at last blue.

When indigo is digested in concentrated sulphuric acid, it is converted into a peculiar blue substance, to which Mr Crum, who first investigated its nature, has given the name of cerulm. When potash is added to the acid solution previously diluted with water, a deep-blue precipitate is formed. All the salts of potash are capable of precipitating this blue matter from its solution. The precipitate consists of the cerulin and the salt employed to throw it down. If we employ acetate of potash, we may wash out this salt by means of alcohol, and leave the blue matter in a state of purity. It is a compound of cerulin and sulphate of potash, and has been called by Mr Crum cerulio-sulphate of potash.

While moist it has so deep a blue colour, as to appear black. When dry it has a shining copper-red colour. By transmitted light it is blue. It attracts water from air with great rapidity. Cold water dissolves τ ⅜θth of its weight of it, and hot water is a much better solvent. Its colouring power is so great that water holding ⅛ θ 0o0O t ^ 1 of its weight in solution is distinctly blue coloured. All water added to its solution precipitates a little of it, except distilled water. W r hen heat is applied to it, it does not melt, nor do any purple fumes rise from it. When a luminous object, as a candle, is viewed through the blue solution of this substance, it appears red. A single drop of nitrate or sulphate of copper added to the liquid makes the candle appear blue. Zinc produces the same effect, though not so powerfully. Mr Crum has shown that cerulin differs from indigo merely by containing four atoms of water, or their elements, united to one atom of indigo. Hence its constituents are,
[table]

If the action of the sulphuric acid on indigo be stopped at a certain point, a new substance is produced, to which Mr Crum, who first obtained it, has given the name of phenicin. It may be obtained in the following way:

Prepare a quantity of indigo by boiling it in sulphuric acid diluted with thrice its weight of water. Then wash it well and dry it. Mix one part of this purified indigo with seven or eight parts of concentrated sulphuric acid in a stoppered phial, and agitate the mixture occasionally till it becomes of a bottle-green colour. Then mix it with a large quantity of distilled water, and throw it on a filter. By continuing to wash the filter with distilled water, the liquid, which at first passed through colourless, becomes more and more blue; and after some time all the indigo which has been changed passes through blue. This blue liquid contains the phenicin in solution. Add to it chloride of potassium, and the phenicin falls down in the state of a fine reddish-purple colour, similar in appearance to the vapour of sublimed indigo. Collect it on a filter, and wash it till the liquid passing through gives a red precipitate with nitrate of silver. It may then be dried.

When dry it has a brownish-black colour. Heated in a crucible, it gives out a little vapour of indigo. When burnt it leaves about fifteen per cent, of ashes, consisting of sulphate and muriate of potash. It dissolves both in water and alcohol, and the solutions are blue; and it is precipitated of its original colour by any soluble salt whatever. Acids do not prevent this precipitation.

From the analysis of this substance by Mr Crum, it appears that it is a compound of one atom of blue indigo and two atoms of water. The constituents are,
[table]

Sect. VIII.- Of Oils.

These have been already described in a former part of this article.

Sect. IX.— Of Camphor.

This substance possesses a good many points of resemblance with the volatile oils, but differs so much in other [7:6:489] respects that it deserves to be considered as a peculiar vegetable principle.

It is obtained from different species of laurus, particularly the camphora and Sumatrensis, and comes to Europe from Japan and the Indian islands Borneo and Sumatra. It is said to be obtained by distilling the wood along with water in large iron pots, to which are fitted earthen heads stuffed with straw. The camphor sublimes and concretes upon the straw in the form of a gray powder. It is afterwards refined in Europe by a second sublimation.

. Pure camphor is a solid substance, having a white colour, a peculiar aromatic odour, and a strong, hot, and somewhat acrid taste. Its, specific gravity is 0-9887. When slowly sublimed, or when a hot alcoholic solution is left at rest, it crystallizes in octahedrons or in hexagonal plates. It is soft enough to be squeezed flat between the fingers, but it,is somewhat tough, and cannot be reduced to powder unless we add a little alcohol. It un-ι dergoes no alteration when left exposed to the air.

When heated to 347° it melts into a transparent and colourless liquid. At 400° it boils. It sublimes completely without any decomposition whatever. When mixed with six times its weight of clay, and distilled, it undergoes decomposition, giving a yellow-coloured aromatic oil, with a little acid water, in which a portion of the oil is dissolved. In the retort remains the clay, mixed with charry matter. When the vapour of camphor is passed through a red-hot porcelain tube, it is partly decomposed, furnishing a volatile oil, which contains undecomposed camphor in solution, together with a considerable quantity of inflammable gas, composed of carbon and hydrogen, apparently in equal atomic proportions, and therefore constituting simple carbo-hydrogen. Camphor, in the open air, burns with’a clear flame and much smoke, and burns all away without leaving any residue.

Camphor is very little soluble in water, requiring about 1000 times its weight of that liquid to dissolve it. Potash precipitates it from its aqueous solution, but neither soda nor ammonia. It dissolves readily in alcohol, 100 parts of alcohol of 0 ’ 806 dissolve 120 parts of camphor at the temperature of 54°. The alcoholic solution is precipitated by water. The alcohol may he distilled off, but it carries a portion of the camphor with it. It is soluble also in ether, and in fixed and volatile oils. 3 .,

It may be fused with sulphur or phosphorus, and the fused mass is soluble in bisulphate of carbon. With iodine it combines into a brown, soft, deliquescent mass. If this compound be dissolved in oil of turpentine, and alcohol be added to the solution, the alcohol takes up the whole camphor, and leaves the combination of iodine and oil of turpentine undissolved. .. *α '<

One part of camphor combines with eleven parts of concentrated sulphuric acid to a brownish tough mass, whiclι is soluble in alcohol but water throws down almost the whole of the. camphor unaltered.. When the sulphuric acid solution is heated, sulphurous acid is given out, and an oil may be distilled, over r .smelling of peppermint and camphor. Finally, there passes.over a little sulphuretted hydrogen, while in the retort there remains a mixture of charcoal, artificial tannin, and sulphuric acid.

One part of* nitric acid dissolves six parts of camphor to an oily-looking liquid. By agitation with water the acid is removed, and thõ Camphor remains unaltered. This nitrated solution of camphor dissolves readily in alcohol. Metals do not dissolve well in it, because a portion of the acid is neutralized by the camphor. When camphor is distilled repeatedly witl‰ 1 eight tirqes its weight of nitromuriatic acid, it is gradually converted into camphoric acid. ∙.. √ , ,f∙a 1 ->∙∙∙ ι . <,. ,

Camphor absorbs 144 times its bulk of muriatic acid gas, and is converted to a clear colourless liquid, which, when exposed to the air, soon crystallizes, because the acid absorbing moisture allows the camphor to separate. One part of camphor is dissolved in 2∙6 parts of concentrated muriatic acid, and is again precipitated by the addition of water.

Camphor has very little affinity for the saliform bases. It is neither dissolved by caustic alkalies nor their carbonates, and it scarcely absorbs its own volume of ammoniacal gas.

Camphor has been repeatedly subjected to analysis by different chemists. The following little table exhibits the result of these experiments.
[table]

Being ignorant of the atomic weight of camphor, these analyses do not enable us to give the atomic constituents with certainty; but the smallest number of atoms which approach near the results of Saussure’s analysis are the following:
[table]

This would make the atomic weight of camphor seven, or some multiple of that number. The analysis of Dr Thomson indicates a greater number of atoms of hydrogen than of carbon, in the proportion of 8J carbon to 10 hydrogen; and the great volatility and other similar qualities which camphor possesses is rather favourable to that notion.

Sect. X.— Of Resins.

Resins are to be met with in almost all plants. They constitute, of course, one of the most abundant and most important of the vegetable principles. They frequently exude spontaneously from trees; they often flow from artificial wounds, and very frequently they are held in solution by volatile oils, from which they maybe freed by distillation. It is easy to obtain them in a state of tolerable purity, by the following process:

Digest the vegetable substance containing resin in alcohol. Filter the liquid, and mix it with water. The resin falls down, and may be collected and washed on the filter. When dry, it may be melted into a mass; but in this state it may be contaminated with various vegetable principles, which are soluble in alcohol; and we have no evidence that different species of resins are not mixed or combined together. For example, colaphon or common rosin is completely soluble in alcohol, but only partially soluble in naphtha. Is it not probable from this that it consists of two distinct resinous bodies, one of which is soluble in naphtha and the other not? Anim^ and elemi may be divided each into two distinct resins by means of alcohol; cold alcohol dissolving one of them, and not acting on the other, which however is soluble in boiling alcohol.

The chemical characters of resins are, that they are soluble in alcohol, but insoluble in water; and that when heated they melt without any thing being volatilized except by decomposition.

.They do not crystallize, but, like gums, are amorphous. They are usually translucent, and have different shades of colour, most commonly brown, though some of them are transparent, and almost colourless. Their specific gravity varies from 0∙92 to 1∙2. In general they are heavier than [7:6:490] water. Their consistence varies considerably, some are hard, and break with a vitreous fracture, and are easily pounded in a mortar; others are soft, or almost liquid; but this generally proceeds from the presence of a volatile oil. When rubbed they usually become negatively electric.

They are insoluble in water, but dissolve in alcohol, both cold and hot; but their solubility varies very much. These solutions redden litmus paper, but not syrup of violets. When they are mixed with water they become milky, and the resin gradually falls to the bottom. They are soluble also in ether and the volatile oils. They may also be dissolved in the fixed oils. By fusion they may be combined with sulphur, and in some measure with phosphorus. Chlorine frequently bleaches the powder of a coloured resin, and renders it white. They dissolve readily in bisulphide of carbon.

For acids they have very little affinity. Concentrated sulphuric acid dissolves them without decomposition. The solution is precipitated by water. When it is heated sulphurous acid is evolved, and there remains a coaly mass, mixed with some artificial tannin. Nitric acid dissolves them with the assistance of heat. The solution at first is precipitated both by water and alkali. If the action be continued some time longer, when the solution is concentrated, a dark-yellow, tough substance is obtained, soluble both in water and alcohol. At last there is formed a bitter-tasted, resinous powder, together with some artificial tannin. Sometimes oxalic acid is formed, as when nitric acid is made to act on guaiacum.

With alkalies and the salifiable bases in general the resins combine readily and form salts, which, when the base is potash or soda, are soluble in water. These combinations have been long known and considered as soaps; but Unverdorben has recently shown that they are true salts, and that the resins in them act the part of weak acids. When resin in excess is digested in a concentrated solu» tion of potash, it is dissolved; and if the solution be diluted with water and filtered, a neutral compound is obtained, the excess of the resin being separated by the dilution. Pulverized resin left in contact with ammoniacal gas over mercury, absorbs it, and forms a neutral compound, sometimes soluble and sometimes insoluble in water. The alkaline earths, in like manner, may be combined with resins, and they generally form salts very little soluble in water, while the salts formed by the earths proper, and the metallic oxides by means of double decomposition, are all insoluble in water.

The resins have been analysed by different chemists, and shown to be compounds of carbon, hydrogen, and oxygen. But it is not worth while to give the numerical results, because we have no method of obtaining individual resins in a state of purity. Of course our results cannot be satisfactory.

Resins are of two kinds, liquid and solid. The liquid resins are in fact combinations of resin with a volatile oil. They are usually called balsams. The most important of these liquid resins are,

1. Balsam of Capaiva, from the capaifera officinalis, a tree whiclι grows in South America and some of the West India islands.

2. Opobalsamum, or balm of Gilead, from the amyris Gileadensis, a tree which grows in Arabia, especially near Mecca.

3. Balsam of Peru, from the Myroxylon Peruiferum, a tree which grows in the warm parts of South America.

4. Styrax, from the Liquidambar styraciflua.

The following is alist of the most remarkable solid resins:

1. Benzoin.

2. Storax.

3. Dragon’s blood.

4. Rosin or colophon.

5. Mastich.

6. Guaiacum.

7. Sandarach.

8. Elemi.

9. Tacamahac.

10. Animé.

11. Labdanum.

12. Botany Bay resin.

13. Black poplar resin.

14. Jalap resin.

15. Copal.

16. Lac.

17. Amber.

Sect. XI.— Of Gum Resins.

The substances called gum resins (because they are partially soluble both in water and alcohoD, have long attracted the attention of apothecaries and physicians, in consequence of the active properties which they possess. They consist of the milky juices which exude from various plants, and which, when left exposed to the air, gradually harden into solid matter. The milky juice of the lactuca virosa, of leontodon taraxicum, of the chelidonium majus, &c. may be mentioned as examples. The chemical characters which these gum resins have been observed to possess are the following:

They dissolve with difficulty and incompletely in water, and when the water containing them is agitated or triturated in a mortar, a milky liquid is formed, from which the undissolved portion precipitates very slowly.

Alcohol dissolves them also incompletely, leaving from one half to one fifth of the gum resin undissolved; but the solution is transparent. Weak spirit is the best solvent, because it is capable of taking up resin, gum, extractive and saline matter, all at once.

They are soluble in dilute alkaline solutions, with the exception of any portion of saline base which they may contain.

Acids act upon them nearly as upon resins. Sulphuric acid converts them into a mixture of artificial tannin and charcoal. Nitric acts upon them with energy, converting them first into a brittle mass, and then, with the assistance of heat, dissolving them.

Their specific gravity is rather higher than that of the resins.

The gum resins may be divided into three classes, the fetid, the drastic, and the aromatic.

I. Fetid Gum Resins. — The principal fetid gum resins are the five following.

1. Assafoetida, obtained from the ferula assafoetida, a perennial plant which is a native of Persia. It comes to Europe in small grains of different colours. At first it is light yellow, but becomes much darker by keeping. Its taste is acrid and bitter, and its smell strongly alliacious and fetid. Its constituents, according to the analysis of Brandes, are as follows:
[table]
[7:6:491]

2. Ammoniac is said to be obtained from the roots of the Heracleum gummiferum, and to be collected in Libya, Abyssinia, and Upper Egypt; but this is somewhat uncertain. It is in small pieces, agglutinated together, and has much the appearance of tallow or wax. Its taste is a nauseous sweet, mixed with bitter, and its smell alliacious. Its constituents, according to the analyses of Bucholz and Braconnot, are as follows:
[table]

3. Opoponax, from the pastinaca opoponax, a plant which is a native of the countries round the Levant. It is in lumps, of a reddish-yellow colour, and white within. Its smell is peculiar, and its taste bitter and acrid. Its constituents, according to the analysis of Pelletier, are as follows:
[table]

4. Sagapenum, supposed to be obtained from the ferula Persica, and to come from Egypt. It is usually in tears, agglutinated together. Colour yellow, taste hot and bitter, smell alliacious. Its constituents, according to the analysis of Brandes, are,
[table]

5. Galbanum, from the bubon galbanum, a plant which grows in Africa and in Syria. It comes to us from the Levant in tears. It has a yellowish-white colour, an acrid and bitter taste, and a peculiar smell. Its specific gravity is 1∙2l2. Its constituents, according to the analyses of Meissner and Pelletier, are as follows:
[table]

II. Drastic Gum Resins. — These, when given in small doses, act as violent purgatives.

1. Scammony, from the convolvulus scammonia, a climbing plant which grows in Syria. The colour is dark gray, or almost black. The smell is peculiar and nauseous, the taste acrid and bitter. The constituents of the two varieties of scammony, from Aleppo and from Smyrna, according to the analyses of Bouillon Lagrange and Vogel, are as follows:
[table]

2. Gamboge or gurngutt, from the stalagmitis gambo-gioides, and, it is said, also other, plants which grow in the East Indies. It is brought to Europe in large cakes. Its colour is yellow; it is opaque. It has no smell, and very little taste. Its specific gravity is 1∙221. According to Braconnot, it is a compound of four parts resin and one part bassorin; according to John, of about nine parts resin and one part gum.

3. Euphorbium, from the Euphorbia officinalis and some other species which grow in the interior of Africa. It is imported in larger or smaller pieces. It has a yellowish colour, and is often very impure. It is destitute of smell, and has at first no taste; but it leaves a sharp impression in the mouth, and excites an inflammation in the gums and tongue. Its constituents, according to the different analyses which have been made of it, are as follows:
[table]

III. Aromatic Gìim Resins. — These are not much employed in medicine, as their effects are not so remarkable on living beings as those of the two preceding sets.

1. Myrrh is obtained chiefly from Abyssinia and Arabia, and there is some doubts about the plant which yields it. Bruce considers it as a mimosa. According to others, it is the amyris kataf. It is in the form of tears, having a reddish-yellow colour, a peculiar smell, and a bitter and aromatic taste. Its constituents, according to the analyses of Braconnot and Brandes, are as follows:
[table]
[7:6:492]

2. Olibanum is the frankincense of the ancicnts. It is brought to London from various places, among others from the East Indies; but the Indian olibanum is least esteemed. Lamarck is of opinion that the Arabian olibanum is from the amyris Gileadensis. The Indian comes from the Boswellia serrata. It is a semitransparent, brittle, whitish-yellow substance; its taste is acrid and aromatic, and when burnt it diffuses an agreeable odour. Its constituents, according to the analysis of Braconnot, are,
[table]

3. Caranna is obtained either from the amyris caranna or the bursera gummifera. It has a dark-brown or greenish-brown colour, and its specific gravity is 1T24. While cold it has a slight smell, similar to that of gum ammoniac; but its smell when heated is aromatic. Its taste is bitterish and resinous. It contains at least ninety-six per cent, of resin, with a trace of volatile oil. There arc present also 0∙4 of malate of potash, with some glutinous matter, and 3∙6 of foreign bodies. It hardly, therefore, deserves to be considered as a gum resin, but rather as a resin.

4. Bdellium comes from the Levant, and is supposed to be the produce of the daucus gummifer, though this is not certain. It is in yellowish transparent tears. When triturated between the teeth it becomes soft. Its specific gravity is 1∙371. According to the analysis of Pelletier, its constituents are as follows:
[table]

Sect. XII.— Of Caoutchouc.

This valuable substance, which has of late years been employed so extensively by Mr MTntosh to render cloth impervious to water, was first brought to this country from South America about the beginning of the last century; and, under the name of Indian rubber, was employed to efface the traces of black-lead pencils from paper. It exudes in a liquid state from a considerable number of trees both in South America and India; the hevoca caoutchouc and guianensis, the iatropha elastica, artocarpus integri-folia, urceola elastica, smilax caduca, and a good many other plants. When these plants are punctured, there exudes from them a milky juice, which, when exposed to the air, gradually lets fall a concrete substance, which is caoutchouc.

Caoutchouc, when pure, is of a white colour, and without either taste or smell. The blackish colour of the common caoutchouc is owing to the method of drying it. The usual way is to spread a thin coat of the milky juice upon the mould, and then to dry it by exposing it to smoke; afterwards other coats are spread out, which are dried in the same way.

It is soft and pliable like leather, and very elastic, so that it may be forcibly stretched out .far beyond its natural length, and instantly recovers its former bulk when the force is withdrawn. Its specific gravity is 0∙9335. It is not altered by exposure to the air. It is insoluble in water, but if boiled in water its edges become transparent, and so soft, that when two of them are pressed together they adhere as closely as if they formed one piece.

It is insoluble in alcohol, but soluble in ether. It dissolves also in volatile oils and in coal naphtha; but to pro duce such a solution a considerable interval of digestion is requisite. The caoutchouc is gradually softened into a kind of jelly, which is afterwards dissolved in the naphtha. It is by spreading several coatings of this naphtha solution between two folds of cloth that the cloth of Mr M‘Intosh, which is impervious to water, is made. The solution is laid on by machinery, the two plies of cloth are laid upon each other, and then the whole is passed between a pair of rollers. Finally, it is dried by exposure to the air in a dry place.

When caoutchouc is heated to 248° it begins to alter its appearance, and when the temperature is increased it melts into the consistency of tar. When the heat is withdrawn it still continues in this semifluid state. When still farther heated it takes fire and burns with a strong flame, and diffuses a fetid odour. In South America it is used instead of flambeaux.

Caoutchouc is not acted on nor dissolved in dilute acids. Even concentrated sulphuric acid acts very imperfectly while cold, though the digestion be continued for a considerable time. When heat is applied sulphurous acid is disengaged, and the caoutchouc is reduced to the consistency of turpentine. Water throws down from this liquid a resinous-looking substance, which hardens when exposed to the air. Nitric acid renders it yellow, and when the concentrated acid is assisted by heat, the caoutchouc is dissolved with a dark-brown colour, and with the evolution of nitrous gas. Water, when poured into the solution, throws down yellow flocks, which are soluble in alcohol, acids, and alkalics, but not in volatile oils. Caoutchouc is insoluble in alkaline leys, even when concentrated and boiling hot.

According to the analysis of Faraday, the constituents of caoutchouc are,
[table]

This corresponds nearly with
[table]

But as we are not acquainted with any definite compounds into which caoutchouc enters, this analysis does not enable us to form any conception of the number of atoms which it contains, or even of its atomic weight.

division ii— of animal bodies.

The constituents of the animal kingdom are probably of a still more complex nature than those of the vegetable. They are distinguished from the greater number of the vegetable bodies by the presence of azote, which in general constitutes one of their essential constituents. Scarcely so much progress has been made in the investigation of animal principles as in that of vegetable, and those which have been well characterized are much fewer. On that account we shall not attempt any classification of animal principles, but satisfy ourselves with giving a short account of the animal secretions, and the most important constituents of animal bodies; and under their respective secretions we shall give the character of those animal principles which are peculiar to them.

CHAP. I.—OF BLOOD.

Blood is a fluid which circulates in the veins and arteries of the more perfect animals. In the veins it has a deep brownish-red colour, but on exposure to the air it becomes scarlet. The blood in the arteries has a scarlet [7:6:493] colour. It has considerable consistency, and an unctuous feel, as if it contained soap. Its specific gravity is about 1Ό527, but it varies somewhat in different animals, and even in the same animal at different times.

When blood, after being drawn from an animal, is allowed to remain for some time in a state of rest, it coagulates into a gelatinous-looking mass. This mass gradually separates into two parts, one of which is fluid, and is called serum ; the other, which is a tough, gelatinous-looking matter, is called the crassamentum or coagulum. The serum is greenish yellow, but the coagulum is red. The proportions between the serum and crassamentum are very various, according to the health or disease of the animal. But it is difficult to determine the point with accuracy, because we cannot free the crassamentum from all remains of serum. We may state the scrum at 56, and the crassamentum (freed from scrum as much as possible by blotting paper) at 44. But in the Asiatic or malignant cholera these proportions are nearly reversed, the crassamentum constituting about sixty of the blood, and the serum only about forty parts.

I. The serum or liquid portion of the blood has a light greenish-yellow colour. It has the taste, smell, and feel of blood; though its consistence is not so great. Its mean specific gravity is 1-0287. It gives a green colour to syrup of violets; but Herman affirms that it reddens litmus, and that, when it is mixed with some sulphuric acid and distilled, it gives out a small quantity of acetic acid. If acetic acid be present, it must be in combination with an alkali; for it has been ascertained by r many experiments that the serum of healthy blood contains a small quantity of uncombined soda.

When serum is heated to the temperature of 159°, it coagulates precisely as the white of an egg does, and for the same reason; it contains a notable quantity of albumen. Of Albumen.

Albumen, not in a state of absolute purity, but tolerably pure, may be procured my mixing the fresh white of an egg with water, and, after the portion which does not dissolve in the water has fallen to the bottom, pouring off the clear solution. It consists of a solution of albumen in water. No method of freeing it from salivin, with which it is always mixed in the white of an egg, has yet been discovered.

. The aqueous solution of albumen is a viscid liquid, having but little taste. It may be freed from water by evaporation at a low heat, and then the albumen is left in the state of a translucent crust, having considerable lustre. It may be employed to cement pieces of paper together. When the aqueous solution of albumen (containing four parts water and one part albumen) is heated to the temperature of 159°, the albumen coagulates, and separates in white flocks, similar to the appearance of the white of a boiled egg. Alcohol and acids have the property of coagulating albumen as well as heat, with the exception of acetic acid, which is destitute of that property. There are some salts also which possess the same property. The coagulation of albumen takes place in close vessels, as well as in the open air.

When coagulated albumen is washed and dried, it forms a translucent, firm, and somewhat elastic crust, having a yellow colour, and a good deal the appearance of horn. When steeped in water, it resumes its former appearance, but is no longer soluble in water, as it was before its coagulation.

When a solution of albumen in water ïs exposed to the action of galvanism, the albumen coagulates round the negative wire; but when the galvanic battery is very powerful, the albumen coagulates on both poles. Probably in this case the coagulation is occasioned by the heat of the wires.

When coagulated albumen is put into water, and heated in a digester to a temperature not lower than 390°, a solution of the albumen is obtained, having a brownish-yellow colour, soluble both in water and alcohol, and resembling osmazome in appearance. There remains undissolved a glue-like matter, little soluble in water, and not at all in alcohol.

The solution of uncoagulated albumen in water soon putrifies, but coagulated albumen is not so liable to undergo this alteration.

Albumen in solution in water is precipitated white by corrosive sublimate. The infusion of nutgalls forms with it a yellowish precipitate, of the consistence of pitch, and insoluble in water. But the infusion of nutgalls is not a very delicate test of albumen, not being capable of detecting less than 1 η⅛0th part of that substance when in solution in water.

When into an aqueous solution of albumen a little acetic acid is added, and then some prussiate of potash is dropt in, a white precipitate appears. This is one of the most delicate tests of albumen that we have it in our power to employ.

From the experiments of Hatchett, there is reason to believe that nitric acid is capable of converting coagulated albumen into gelatine.

Albumen has been analysed by different chemists with considerable care. The following table exhibits the results of these experiments:
[table]

If we consider the analysis of Prout as most accurate, it will indicate the atomic constituents of albumen to be
[table]

so that its atomic weight is 11-25, or some multiple of that number.

λVhen coagulated serum is broken in pieces, a small quantity of liquid oozes out, which has been called the serosity. The saline contents of this liquid are somewhat increased by washing the coagulated serum well with distilled water. This liquid contains some common salt and some soda, together with a few other salts. The constituents of 1000 parts of serum, as determined by Berzelius, are as follows:
[table]
[7:6:494]

II. The crassamentum of the blood is scarlet coloured, containing all the colouring particles. But it is difficult to free it completely from the serum. This may be done as far as possible by placing it on bibulous paper, till the paper refuses to imbibe any more moisture. It may now be considered as consisting of jibrm and colouring matter. The latter of these is soluble in cold water, but not the former. Hence we may obtain the fibrin by washing the erassamentum in cold water till the red colour is removed.

Of Fibrin.

Fibrin exists also in the muscles of animals, as well as in blood, and constitutes the fibrous part of the muscle. Hence the origin of the term fibrin.

Fibrin, when pure, is brownish yellow, and has little or no taste or smell. When newly extracted from blood it is soft and elastic, and resembles the gluten of wheat. Its colour deepens very much in drying.

It is not altered by exposure to the air, nor is it speedily decomposed though kept under water. It is insoluble in cold water. In boiling water it curls up, and after the boiling has continued for some hours, the water becomes opal-coloured, but no gas is evolved. When infusion of nutgalls is dropt into the water, white flocks precipitate, which do not adhere together, as the precipitate formed in solution of gelatine. The evaporated liquid does not gelatinize, and leaves a white, dry, hard, friable residue, soluble in cold water, and having a taste resembling that of fresh broth.

Fibrin dissolves in acetic acid; and when the solution of prussiate of potash is dropt into the solution, a white precipitate falls, as is the ease with the solution of albumen in the same acid; but fibrin, by long boiling in water, loses its property of softening and dissolving in acetic acid.

In alcohol of the specific gravity 0∙81, fibrin undergoes a species of decomposition, and forms an adipoeirous substance, soluble in alcohol, and precipitated by the addition of water. It has often an unpleasant odour. The alcohol solution, when evaporated, leaves a fatty residue. Fibrin, after being heated in alcohol, continues soluble in acetic acid. Ether acts on fibrin in the same way as alcohol does.

In weak muriatic acid fibrin shrinks, and gives out a small quantity of azotie gas; but scarcely any portion is dissolved, even by boiling, nor does the acid liquid afford any precipitate with ammonia or prussiate of potash. The fibrin thus treated is hard and shrivelled. When repeatedly washed with water, it is at last converted into a gelatinous mass, which is soluble in water. It is a compound of fibrin and muriatic acid.

Concentrated sulphuric acid decomposes and earbonizes fibrin. This acid, when diluted with six times its weight of water, acquires a red colour if digested in fibrin, but dissolves scarcely any thing. The fibrin combines with sulphuric acid; and when it is deprived of the excess of acid by washing it with water, the compound becomes capable of being dissolved in water.

Nitric acid of the specific gravity of 1∙25, digested in fibrin, renders it yellow, and diminishes its cohesion. The fluid becomes yellow, and the surface of the fibrin is covered with a small quantity of fat formed by the action of the acid. During this process pure azotie gas is disengaged. After twenty-four hours digestion the fibrin is converted into a pulverulent mass of a yellow colour. By washing it becomes orange. It is a compound of fibrin and nitric acid.

In caustie alkalies fibrin increases in bulk, becomes transparent and gelatinous, and at length is completely dissolved. The solution is yellow, with a shade of green. Aeids occasion in it a precipitate, which gradually becomes confluent. Alcohol occasions a precipitate in it. No soap is formed.

When fibrin is exposed to heat it contracts suddenly, and moves like a bit of horn, exhaling at the same time the smell of burning feathers. In a strong heat it melts. When exposed to destructive distillation it yields water, carbonate of ammonia, a heavy, fetid oil, traces of acetic acid and heavy inflammable air, and it leaves a quantity of charry matter.

Fibrin has been subjected to analysis in order to determine its constituents. The following table exhibits the results of these analyses:
[table]

If we adopt Michaelis’ analyses, the following will be the ratios of the atomic constituents in arterial and venous blood:
[table]

If any confidence could be put in these analyses, it is clear that arterial blood contains more earbon and more azote and oxygen than venous blood; but many repetitions of these analyses will be requisite before any certain conclusions can be drawn from them.

The fibrin usually constitutes about the third part of the crassamentum of blood.

Of the Colouring Matter of Blood.

The other constituent of the erassamentum is the colouring matter. In the living blood it exists in globules, which may be detected under the microscope, and concerning the shape and size of which much has been written. These globules are dissolved when the crassamentum is washed in water; and when the water is evaporated by a gentle heat, we obtain the colouring matter in the state of a dark-red powder, not, however, quite free from albumen.

Its colour is a dark-reddish brown. It is soluble in water, provided it has been obtained by a very low heat; but if we boil the water, the colouring matter is deprived of its solubility altogether.

Its properties (if we except its colour) are very nearly the same as those of albumen and fibrin. It combines with acids like these bodies, and forms compounds, which are soluble in water. Alkalies dissolve it, and the solution has a purple colour. The alkaline solution is precipitated by alcohol, which, however, acquires a red tinge.

There is a considerable difference in the properties of this substance, as described by different chemists. The colouring matter of blood, as described by Brande, is quite different from that of Berzelius; while the character assigned it by L. Gmelin differs from those of the other two chemists. It is evident from this that colouring matter in a state of complete purity has not yet been subjected to . examination. That of Berzelius was obviously mixed with a great deal of albumen.
[7:6:495]

When the colouring matter of blood is incinerated, the ashes are found to contain half their weight of red oxide of iron; yet no iron can be detected before the incineration. To the presence of this iron the red colour of the globules has been ascribed by some chemists; but this opinion does not seem to be well grounded. If the iron existed in blood in the state of red oxide, its presence would certainly be detected by re-ågents. The impossibility of detecting it would seem to show that it exists in blood in the metallic state.

The colouring matter in the crassamentum is about twice as heavy as the fibrin.

CHAP . II.—OF SALIVA.

This fluid is secreted by a set of glands which discharge it through ducts into the mouth. Its quantity is considerable, though it would be difficult to determine it with precision. It is transparent and colourless, but has a good deal of viscidity, and is destitute of taste and smell. Its mean specific gravity is about 1Ό038. When agitated it froths like all other adhesive liquids. W'hen mixed with water, a few flocks of mucus precipitate. It was merely suspended in the saliva, and not dissolved. When saliva is evaporated it swells greatly, and leaves behind it a thin brown-coloured crust; but if the evaporation be conducted slowly, small cubic crystals of common salt are deposited. Saliva contains dissolved in it a peculiar animal principle, which we may distinguish by the name of salivin. It contains also a small quantity of soda and of salts of soda. The following table exhibits the constituents in a thousand parts of saliva, according to the analysis of Berzelius:
[table]

Of Salivin.

Salivin, the speichelstoff of the Germans, exists not merely in saliva, but likewise in some other animal substances. It may be obtained from saliva by the following process: After freeing saliva from mucus, evaporate it to dryness by a gentle heat. Digest the residual matter in rectified spirits, to dissolve the salts. What remains is to be dissolved in water. By evaporating the solution to dryness, salivin remains in a state of tolerable purity.

Salivin is thus obtained in a translucent light-yellowcoloured crust. It dissolves readily in water, and when the solution is heated and concentrated, no coagulation takes place. If the salivin has been dried in too high a temperature it loses its solubility in water. Salivin is insoluble in alcohol. It is not precipitated from water by the infusion of nutgalls. Lime-water, chloride of tin, the nitrate or acetate of lead, and nitrate of mercury, occasion precipitates, when dropt into the aqueous solution of salivin.

In the small intestines of the horse (when the animal is kept fasting for thirty or thirty-six hours before death), there is occasionally found a light-yellow, transparent, and glutinous liquid, which dissolves in cold water. The solution is light yellow, transparent, slightly glutinous, may be passed through the filter, and possesses the following characters: It is not altered or precipitated by a boiling heat, by iodine, chlorine, muriatic acid, nitric acid, or alcohol. It is precipitated by barytes water, lime-water, alum, green vitriol, perchloride of iron, sulphate of copper, protochloride of tin, acetate of lead, nitrate of mercury, nitrate of silver, and chloride of platinum. Corrosive sublimate and tincture of nutgalls render it muddy, but not immediately. Acetic acid gradually throw’s down from it large white flocks. This liquid consists of a solution of a peculiar substance, which has a strong analogy to salivin.

The salivin, and mucus of the saliva, constitute in a great measure the tartar of the teeth. To these two substances, however (if the tartar is not removed), phosphate of lime, with a trace of phosphate of magnesia, is gradually added. The following table exhibits the constituents of tartar, according to the analysis of Berzelius:
[table]

CHAP . III.—OF THE PANCREATIC JUICE.

The pancreas is a gland of considerable size, situated in the abdomen, from which passes a duct which terminates in the duodenum, sometimes separately and sometimes in common with the bile duct. It secretes a liquid which is deposited in the duodenum, where it is mixed with the chyme, and is obviously intended to assist in the digestion of the food. From the situation of the pancreas, it is very difficult to obtain the liquid which it secretes, and which is usually called the pancreatic juice. It was considered as analogous to, if not the very same with, saliva. Francis de le Boé first affirmed that it is acid; and in 1664, R. de Graaf, a disciple and partizan of De lc Boé, collected the pancreatic juice of a dog, and found it limpid and slightly viscid. It was sometimes acid and sometimes only saline in its taste. A controversy took place soon after respecting the nature of this juice, one party affirming it to be acid, and another party to be alkaline. It is only within these few years that we have acquired definite ideas respecting the nature of this liquid, in consequence of the chemical analysis of it by Tiedemann and L. Gmelin. They collected it from dogs, sheep, and horses.

The pancreatic juice from the dog was at first muddy and slightly reddish; but after flowing for some time, it became quite limpid, with an opaline tinge inclining slightly to bluish white. It was viscid, like the white of an egg diluted with water. Its taste was weakly but sensibly saline. In about four hours 154 grains of the liquid were collected.

The pancreatic juice of the horse was of a very pale-yellow colour and limpid, excepting a very slight opaline tinge. It was viscid, like the white of an egg diluted with water. It very slightly reddened paper tinged blue by litmus. In the dog and the sheep the first portion of the pancreatic juice collected was acid. It afterwards became alkaline.

The pancreatic juice of the dog was found to contain an alkaline carbonate and acetate, an animal matter thrown down by the infusion of nutgalls and many other re-actives, and which was considered as osmazome, and another matter reddened by chlorine, which is peculiar to the pancreatic juice, and may therefore be called pancreat'm.

A hundred parts of pancreatic juice from a dog being evaporated to dryness, left 8∙72 of a residue. It was brittle and elastic, of an orange colour, and semitransparent. When a hundred parts of this solid residue was incinerated, the ashes left weighed 8∙28 parts. A hundred parts of the solid portion of pancreatic juice were composed of
[table]
[7:6:496]

The characteristic property of pancreatin is to be reddened by a small quantity of chlorine, and discoloured by a large quantity. This matter is soluble both in water and alcohol, but much more soluble in the former than in the latter.

The pancreatic juice of the sheep was composed of
[table]

The solid matter consisted of
[table]

No pancreatin was found in it.

From these facts, for which we are chiefly indebted to Tiedemann and L. Gmelin, it is obvious that the pancreatic juice is quite different in its nature from saliva.

CHAP . IV.—OF BILE.

Bile is a liquid of a yellowish-green colour, an unctuous feel, bitter taste, and peculiar smell, which is secreted by the liver; and in most animals considerable quantities of it are usually found collected in the gall-bladder. The bile of the ox has been chiefly examined by chemists, being most easily procured.

Its colour is usually greenish yellow, but sometimes green. Its taste is bitter, but at the same time leaving an impression of sweetness. Its smell is feeble, but peculiar and disagreeable. It does not act on vegetable blues. Its consistence varies a good deal, being sometimes a very thin mucilage, sometimes very viscid and glutinous; sometimes it is transparent, but generally contains a yellowcoloured matter, which precipitates when the bile is diluted with water. Its specific gravity is about 1 , 027. When agitated, it lathers like a soap.

It mixes readily with water in any proportion; but it refuses to unite with oil. Yet it dissolves soap, and is often employed to free cloth from greasy stains.

When an acid is added to bile, even in a minute quantity, it acquires the property of reddening vegetable blues. The addition of a little more acid occasions a precipitate, and sulphuric acid occasions a greater precipitate than any other acid. This precipitate consists of a yellow matter, which is insoluble in water. If we continue to add sulphuric acid after the yellow matter has been precipitated, a green matter falls down, formerly denominated the resin of bile. It is a compound of picromel (or the peculiar matter of bile), and of the precipitating acid.

The following table exhibits the constituents of 1000 parts of ox bile, according to the analysis of Berzelius:
[table]

Of Picromel.

This substance, which is the characteristic constituent of bile, may be obtained by the following process: Drop a little sulphuric acid into bile, in order to separate the yellow matter which it may contain. Separate the fluid part from the precipitate, then add fresh sulphuric acid as long as any precipitate appears. This precipitate has a green colour, and is what chemists have been in the habit of distinguishing by the name of resin of bile. Wash it with water, and then digest it with carbonate of barytes and water for some time. The barytes will combine with the sulphuric acid, while the picromel will dissolve in the water. Evaporate the aqueous solution to dryness by a gentle heat. Pure picromel remains behind.

Picromel resembles entirely inspissated bile. It has a green, or rather yellowish-green colour, and a bitter taste, followed by an impression of sweetness. It is soluble in water and in alcohol, in all proportions. Ether does not dissolve it, but converts it into an adipocirous substance, having a very disagreeable smell.

It has the property of combining with acids, and of forming compounds soluble when neutral, but insoluble, or only sparingly soluble, when there is an excess of acid. It unites also with many metallic oxides, constituting with them a pulverulent mass.

It is not precipitated by infusion of nutgalls, but nitrated suboxide of mercury, diacetate of lead, and the salts of iron, occasion a precipitate when dropt into its aqueous solution.

When picromel is subjected to destructive distillation, it gives out no ammonia, showing the absence* of azote from its constitution. Its constituents are carbon, hydrogen, and oxygen. According to the analysis of Dr Thomson, its constituents arc,
[table]

This corresponds with
[table]

Hence 6-875, or some multiple of it, represents the atomic weight of picromel.

Human bile differs considerably from that of the ox. Its colour is sometimes green, sometimes yellowish brown, sometimes nearly colourless. Its taste is not very bitter. It generally contains some yellow matter suspended in it. When evaporated to dryness, it leaves a brown matter, amounting to about one eleventh of its weight. When this matter is calcined, it yields all the salts to be found in ox bile. All the acids decompose human bile, and throw down a copious precipitate, consisting of albumen and picromel. One part of nitric acid is capable of saturating 100 parts of bile. The acetate of lead throws down the picromel, and leaves a yellowish liquid, containing the salts of bile, and a small quantity of a peculiar matter, the nature of which has not yet been determined. The following table exhibits the constituents of human bile, as determined by the analysis of Berzelius:
[table]

CHAP . V.—OF MUCUS.

All the different passages and cavities of the living body through which liquids, air, or any substance likely [7:6:497] to prove injurious to the organ is destined to pass, are supplied with a quantity of secreted semifluid, destined to protect them from the injurious action of these foreign bodjes. Thus the nostrils and the trachaea, through which air is continually passing during the continuance of life, is supplied with a matter to defend therħ, usually called the mucus of the nose and trachaea. In like manner the ureters, the bladder, and urethra, are covered with mucus, to protect them from the action of the urine. The mouth, oesophagus, stomach, and intestines, are also covered with mucus, to protect them from the injury which they might sustain from the food. To these semifluid substances the common term mucus has been applied, though they are far from agreeing exactly in their chemical constitution; and the membranes which throw out this substance are distinguished by anatomists by the name of mucous membranes.

The animal matter peculiar to mucus is the same in all cases, and has the following properties. It is insoluble in water, but is able to imbibe so much of that liquid as to become more or less transparent, and semifluid, or glairy as it is termed. If in this state it be laid on bloating paper, and the paper be changed as it becomes wet, the mucus may be deprived of the greater part of the moisture which it had absorbed, and will then have lost most of its peculiar properties. Mucus is not coagulable by boiling; it becomes transparent when dry, and generally resumes its mucous character on adding fresh water; but there is a great difference in this respect in the mucus from different parts of the body.

The liquid part of mucus, or that fluid which the proper mucous matter imbibes, and to which it owes its fluidity, is the same thing as the serosity, or the liquid which oozes out of coagulated serum.

1. Mucus of the Nose. — The constituents of this matter, as analysed by Berzelius, are as follows:
[table]

Nasal mucus, when just secreted, contains only 0∙25 per cent, of solid matter. The peculiar animal matter seems at first to be held in solution by the soda, and to be precipitated as the alkali becomes carbonated.

The proper mucous matter of the nose has the following properties. When immersed in water it imbibes so much moisture as to become transparent, excepting a few particles that remain opaque. It may then be separated by the filter from the rest of the water, and may be further dried on bloating paper, till it has again lost nearly all the water it had imbibed. It may be made to imbibe water, and dried alternately as often as you please; but the mucous matter gradually becomes yellow, and assumes a resemblance to pus. Five parts of recent mucus imbibe ninety-five parts of water, and form a glairy mass, so thick that it cannot be poured from one vessel to another. When this mucus is boiled with water, it doeá not become horny, nor does it coagulate. It is broken in pieces, but collects again unaltered at the bottom of the vessel, when the boiling is finished. But we must, to obtain this result, separate, in the first place, a little albumen which it contains, by means of cold water.

It is soluble in dilute sulphuric acid. Concentrated sulphuric acid chars it Nitric acid at first coagulates it; by continuing the digestion it softens, and is finally dissolved into a clear yellow liquid. Acetic acid hardens mucous matter, but does not dissolve it even at a boiling temperature. Caustic alkali at first renders mucous matter more viscid, and afterwards dissolves it into a limpid liquid. Tannin coagulates mucus, both when softened by the absorption of water, and when dissolved either in an acid or an alkali.

2. Mucus of the Trachaea. — The mucus of the trachaea is exactly similar to that of the nose. The bluish or darkcoloured flocculi expectorated in the morning will imbibe twenty times their bulk of water, and become so transparent as hardly to be visible. The action of acids and alkalies is the same on it as on nasal mucus.

3. Mucus of the Gall-Bladder. — The mucus of the gallbladder much resembles that of the nostrils, but is more transparent, and always tinged yellow by the bile. When dried it may be again softened in water, but loses part of its mucous property. Biliary mucus dissolves in alkali, and its fluidity increases in proportion to the quantity of the alkali. When the alkaline solution is exactly neutralized with an acid, the mixture becomes slightly turbid, and may be drawn out into threads. All the acids produce with biliary mucus a yellowish coagulum, which reddens litmus. The coagulum formed with the sulphuric acid may be restored to its mucous properties by exact saturation with an alkali. Alcohol coagulates this mucus into a very yellow granular mass, to which the mucous property cannot be restored. It is this mucus of the gallbladder which chemists formerly mistook for albumen.

4. Mucus of the Intestines. — This mucus accompanies the excrements, in which it often forms long and transparent filaments. When once dried, the addition of water will not restore its mucous property. Alkalics produce this effect, but without rendering it transparent.

5. Mucus of the Urinary Passages. — It accompanies the urine, in which it is partly dissolved, and partly suspended mechanically. This last portion is generally too transparent to be distinguished by the eye; but it may be exhibited by leaving the urine for some timeat rest, decanting off the fluid part, and collecting the mucus on a filter. It loses its mucous property totally when dried. It then often becomes rose-coloured, and appears as if crystallized. It softens a little in water. The urinary mucus dissolves readily in alkalies, and is not separated from this solution by acids. Tannin separates it in white flocculi.

CHAP. VI.—OF THE FLUIDS OF THE SEROUS MEMBRANES.

The surface of serous membranes is always moistened by a liquid, which is never secreted during health in quantities sufficient for analysis. It is therefore only during a dropsical state of these membranes that we can gain any knowledge of its properties. It seems to be serum deprived of from two thirds to four fifths of its albumen. It does not coagulate by mere boiling; but it gradually becomes turbid; and during the evaporation a coagulated mass collects. This matter seems to be albumen, but it has a sulphur-yellow colour. The following is the result of the analysis of the fluid of hydrocephalus by Berzelius:
[table]
[7:6:498]

Dr Marcet found the constituents of the liquid of spina bifida as follows:
[table]

The other dropsical fluids are in general more concentrated, which may arise either from the mere consequence of being long kept, or from the transudation of the serum of the blood, which always occurs in the last stages of dropsy, and appears also to take place in the urine and cellular membranes.

CHAP . VII.—OF MILK.

Milk is a fluid secreted by the female of all those animals denominated mammalia, and intended for the nourishment of her offspring.

The milk of every animal has certain peculiarities which characterize it. But the animal whose milk is chiefly used by man as an article of food, and with which, of course, we are best acquainted, is the cow. We shall therefore, in the first place, describe the nature and constitution of cow’s milk; and afterwards notice the peculiarities which distinguish from it the milk of other animals.

Milk is an opaque liquid, of a white colour, a slight, peculiar smell, and a pleasant, sweetish taste. It slightly reddens vegetable blues. When allowed to remain for some time at rest, there collects on its surface a thick yellowish unctuous matter called cream.

The milk thus deprived of its cream has a bluish-white colour, and a specific gravity of about 1∙033. Its constituents, by the analysis of Berzelius, are as follows:
[table]

Curd, which is separated from creamed milk by rennet, has some resemblance to coagulated albumen. It is a white solid, and when freed from moisture has a good deal of brittleness.. It is precipitated from milk by acids, and the precipitate consists of casein, combined with the acid employed to throw it down. If we employ sulphuric acid to throw it down, and, after washing it well with water, digest it with carbonate of barytes and water, the sulphuric acid separates, while the casein dissolves in the water. The aqueous solution thus obtained is yellowish, and resembles a solution of gum. When evaporated to dryness it leaves a yellow matter, which is the pure curdy part of milk, or casein as it was called by Proust.

Of Casern.

Casein thus obtained dissolves readily in water. The solution, when boiled in an open vessel, becomes covered with a white pellicle, precisely as milk does, and acquires the smell of boiled milk. The pellicle is almost insoluble in water, and appears to be a product of the action of air on the dissolved casein.

With the mineral acids casein forms similar combinations with those that fibrin and albumen form with the same acids. A great excess of acetic acid is required in order to dissolve casein; and the neutral combination of acetic acid and casein appears to be insoluble. Casein is easily dissolved in alkalies. Its solution in acetic apid, as well as in ammonia, becomes covered with a small quantity of cream every time that the casein has not been well separated from the butter. Alcohol converts casein into an adipocirous and fetid substance.

When casein has been precipitated from milk by alcohol, and the casein thus obtained is put into an aqueous solution of ammonia, it first swells into a glutinous matter; and when an additional quantity of water is added, it dissolves completely. Milk is coagulated by tannin.

Casein has been subjected to an analysis by Gay-Lus- 1 sac and Thenard. They obtained the following constitu- 1 ents:
[table]

This corresponds with
[table]

This makes the atomic weight of casein 8 ’ 625, or some multiple of that number.

When we compare casein with albumen, we see that it contains less hydrogen and oxygen than albumen, but nearly the same proportion of carbon and azote. It is clearly, however, intimately connected with albumen,being intended in milk to answer the same nutritious purposes as albumen does in the egg.

The cream which collects on the surface of milk contains a great deal of whey, and a considerable proportion of casein. A quantity of cream, of the specific gravity 1Ό244, was found by Berzelius composed of
[table]

so that cream may be considered as a kind of emulsion. It is easily decomposed by agitation, absorbing oxygen, and the butter separating. By this process of churning the milk becomes more acid than it was at first.

Butter is of a yellow colour, possesses the properties of an oil, and mixes readily with fixed oily bodies. When heated to the temperature of 96°, it melts, and becomes transparent. When kept melted for some time, some curd and whey separates, and it assumes exactly the appearance of an oil. Butter possesses nearly the same properties as marrow. When treated with an alkali it is converted into butyric acid, the characters of which have been given in a preceding part of this article.

Milk freed from butter and casein is known by the name of whey. It is a thin pellucid fluid, of a yellowish-green colour, and pleasant sweetish taste, in which the flavour of milk may be distinguished. When boiled, an additional portion of casein separates from it. After this separation it is almost colourless, but has still a sweetish and agreeable taste. If it be slowly evaporated, it deposits at last a number of white crystals, which constitute sugar of milk. The other constituents have been stated in the table inserted near the beginning of this chapter.
[7:6:499]

Of Sugar of Milk.

This substance crystallizes in four-sided rectangular prisms, terminated usually by four-sided pyramids. It is translucent and white coloured; its specific gravity 1∙543. At the temperature of 59° it is soluble in five times its weight of water, and in two and a half times its weight of boiling water. By itself it is insoluble in alcohol; but the addition of a little sulphuric acid renders it soluble in that liquid. When heated it emits the odour of caramel, and when burnt exhibits the same phenomena as common sugar does. When distilled it yields similar products with common sugar. It dissolves in muriatic and acetic acids.

Like common sugar, it appears to possess acid qualities, or at least to bç capable of combining in definite proportions with bases. Thus, with oxide of lead it unites in two proportions. The neutral compound appears to consist of
[table]

There is another compound of these bodies, containing four times the quantity of sugar of milk, united to the same quantity of protoxide of lead. We may therefore consider it as a quater-saccholactate, comnosed of
[table]

The crystals of sugar of milk, according to the experiments of Berzelius, arc composed of
[table]

Sugar of milk has been analysed by Berzelius, Gay-Lussac and Thenard, Prout, and Bcrthollet. All the analyses coincide to show that the crystals, or hydrated sugar of milk, are composed of
[table]

Consequently, in the anhydrous state, the constituents must be
[table]

Human milk has a much sweeter taste than cow’s milk. When left at rest a cream collects on its surface, which is more abundant and whiter coloured than the cream of cow’s milk. The milk deprived of cream is much thinner, and is rather a whey with a bluish-white colour than milk. It cannot be coagulated by the ordinary methods; yet it contains casein, for when boiled a pellicle collects on the surface, like what forms when the milk of the cow is boiled. No butter can be procured from human milk by churning. What separates by rest is rather casein than butter. Thus human milk differs from that of the cow by containing less casein, by its oily constituent being so intimately combined with the casein that they cannot be separated by agitation, and by containing rather a greater quantity of sugar of milk.

Ass’s milk has a great resemblance to human milk. It has nearly the same colour, smell, and consistence. When left at rest for some time a cream forms on the surface, but by no means so abundant as on human milk. This cream by long agitation yields a butter, which is always soft, white, and tasteless, and, what is singular, very readily mixes again with the butter-milk; but it may be again separated by agitation, while the vessel which contains it is plunged in cold water. Skimmed ass’s milk is thin, and has an agreeable sweetish taste. Alcohol and acids separate from it a little curd, which has but a small degree of consistence. The serum yields sugar of milk and chloride of calcium.

Goat’s milk, if we except its consistence, which is greater, does not differ much from cow’s milk. Like that milk, it throws up abundance of cream, from which butter is easily obtained. The skimmed milk coagulates just as cow’s milk, and yields a greater quantity of curd. Its whey contains sugar of milk, chloride of calcium, and common salt.

Ewe’s milk resembles very closely that of the cow. Its cream is rather more abundant, and yields a butter which has less consistency than that from cow’s milk. Its curd has a fat and viscid appearance, and is not easily made to assume the consistence of that from cow’s milk. It makes excellent cheese.

Mare’s milk is thinner than that of the cow, but scarcely so thin as human milk. Its cream cannot be converted into butter by agitation. The skimmed milk coagulates precisely as cow’s milk, but the curd is not so abundant. The serum contains sugar of milk, sulphate of lime, and chloride of calcium.

CHAP . VIII.—OF URINE.

Healthy urine is a transparent liquid, of a light amber colour, and an aromatic odour resembling that of violets. Its specific gravity varies a great deal, but most commonly it is between 1Ό15 and 1∙020. Hysterical urine is sometimes as low as 1∙005, and diabetes urine is frequently as high as 1*048. When it cools the aromatic smell leaves it, and is succeeded by another, well known under the name of urinous. This smell gradually disappears, and a fetid ammoniacal odour replaces it.

Urine reddens delicate vegetable blues, and therefore contains a disengaged or imperfectly saturated acid. This acid was at first considered as the phosphoric. Berzelius endeavoured to show that it was the lactic. Dr Prout has shown that urate of ammonia reddens vegetable blues, and that uric acid is so insoluble in water, that the quantity of it in urine could not exist in solution unless it were united with something which increased its solubility. Hence he infers that urinc contains urate of ammonia, dan that this salt produces the observed change on vegetable blues.

When ammonia is dropt into recent urine, a very minute quantity of phosphate of lime falls down in the state of a white sediment. Now phosphate of lime being insoluble in water, but biphosphate being slightly soluble in that liquid, the probability is, that in urine it exists in the state of biphosphate. Now, as biphosphate of lime reddens vegetable blues, this salt doubtless contributes to the effect which urine has on litmus or red cabbage.

If healthy urine be left standing for some time in cylindrical glass vessels, small four-sided rectangular prisms are found deposited in small numbers on the sides of the vessel. These consist of ammonia-phosphate of magnesia. From this it would appear that urine contains a small quantity of biphosphate of magnesia.

If urine be acidulated with nitric acid, to prevent the precipitation of the phosphates of lime and magnesia, and a quantity of chloride of barium be introduced into it, a precipitate of sulphate of barytes falls down. Hence it [7:6:500] appears that urine contains sulphuric acid. This acid is partly combined with potash and partly with soda.

When healthy urine is allowed to cool, small red needles make their appearance in it, sometimes swimming on the surface of the liquid, and sometimes deposited upon the vessel containing it. These needles consist of uric acid, coloured by being united with the colouring matter of urine.

If we concentrate healthy urine by a low heat, and then mix it with some nitric acid, and set it aside for twenty-four hours, a number of brown-coloured plates are deposited, having a silky lustre. These consist of urea combined with nitric acid. They may be deprived of their colouring matter by dissolving them in water and agitating them with ivory-black.^[21. Care must be taken that the ivory black contains no carbonate of lime, otherwise the nitrate of urea will be decomposed. ] If we now add as much potash as will just saturate the nitric acid, nitre will be formed and deposited, and the urea will dissolve in the water. By evaporating the solution, the urea is deposited in beautiful white plates or prisms.

Besides these constituents, urine contains common salt, phosphate of soda, and phosphate of ammonia. When the liquid is sufficiently concentrated, these two last salts unite together and form a double salt, ammonia-phosphate of soda. This salt, when first extracted from urine, drew much attention, and was known by the name of microcos-mic salt.

Urine is said also to contain a small quantity of sal ammoniac. Urine is sometimes precipitated by infusion of nutgalls, and therefore must contain albumen. But this usually happens only in the urine of dropsical patients. When such urine is in the first place mixed with acetic acid, it gives a copious white precipitate with prussiate of potash.

The following table exhibits the constituents of 1000 parts of healthy urine, according to the analysis of Berzelius.
[table]

Of Urea.

Urea may be obtained from healthy urine by the following process. Evaporate the urine to one fourth of its bulk, and mix it with about one third of its weight of nitric acid of the specific gravity 1∙4, and set it aside for twenty-four hours. Many silky plates of nitrate of urea are deposited. Dry them on blotting paper, dissolve them in water, and add as much potash as is requisite to saturate the nitric acid which they contain. Concentrate the solution, and set it aside. Crystals of saltpetre are deposited. Separate these crystals, concentrate the residual liquid, and digest it in alcohol. The alcohol dissolves the urea and colouring matter of urine, but leaves the nitre. Evaporate the alcoholic solution to dryness, dissolve the residue in water, and agitate the solution in a phial with some good ivory-black. The ivory black separates the colouring matter, and the liquid after filtration is a pure colourless solution of urea. By careful evaporation it is deposited in beautiful white and semi-transparent foursided prisms.

Urea has little or no smell. Its taste is strong and acrid, resembling that of the ammoniacal salts. When exposed to the air it attracts moisture, and is converted into a thick liquid. It is exceedingly soluble in water, and during its solution considerable cold is produced. Alcohol dissolves it with facility, and the alcoholic solution yields crystals much more easily than the aqueous.

When nitric acid is dropt into a concentrated solution of urea, a great number of pearl-coloured crystals are deposited. Oxalic acid produces the same effect, but no other acid tried. The infusion of nutgalls gives the aqueous solution of urea a yellowish-brown colour, but causes no precipitate.

When heat is applied to urea, it melts, swells up, and evaporates. When distilled, much carbonate of ammonia is obtained, together with some hydrocyanic acid. Many curious mutual conversions of urea and cyanogen into each other have been lately observed by Wohler, Serullas, &c.

Considerable pains have been taken to determine the constituents of urea, by distilling it at a red heat when mixed with oxide of copper. The following table exhibits the results obtained:
[table]

Dr Prout dried his urea, before analysis, in vacuo over sulphuric acid, at a temperature of 200°. If we consider his result as approaching nearest to the truth, we obtain the following as the atomic proportions of which urea is composed:
[table]

Hence 3∙75, or some multiple of that number, is the atomic weight of this substance. It is easy to see, from this constitution, how, when it is decomposed by destructive distillation, hydrocyanic acid, carbonic acid, and ammonia, may be formed from it.

Urea is doubtless one of the most important of the constituents of urine, and to the changes to which it is liable many of the derangements to which the urinary system is liable may be ascribed. The quantity of it in urine is much greater than that of any of the other constituents of urine, with the exception of the water. We shall now notice some of the most remarkable alterations to which urine is subject.

1. Diabetes. — Diabetes is a disease fortunately of rare occurrence, but still so frequent that every medical man in tolerable practice is pretty sure of meeting with more than one case of it. It is attended with a dry skin, a [7:6:501] ravenous appetite, and the passing of an enormous quantity of sweet-tasted urine. It is always light coloured and of high specific gravity, sometimes as high as 1∙050, and never lower than 1*02, or rather 1∙025. It contains urea, uric acid, and all the usual contents of urine, but in smaller quantity than usual, on account of the enormous quantity of urine discharged, amounting sometimes to twenty-four, or even thirty English pints, in twenty-four hours. Yet the absolute quantity of these constituents thrown out of the system in the course of a day is probably as great as during health. The characteristics of diabetic urine are the enormous quantity and the sweet taste. This sweet taste is owing to the presence of a quantity of sugar, which depends upon the specific gravity of the urine. Sometimes it amounts to as much as thirty ounces in twenty-four hours. This enormous discharge of sugar accounts for the great appetite, the prostration of strength, and the wasting of the system, which accompany this disease.

Whether diabetic sugar belongs always to the same species seems doubtful. The writer of this article met with a case of diabetes some years ago, in which the sugar was of such a nature, that when the urine was concentrated by a gentle heat, and then set aside, beautiful crystals of the sugar were gradually deposited. These crystals were perfectly white, and in regular four-sided prisms slightly oblique. They were not altered by exposure to the air. When the urine containing these crystals was raised to too high a temperature, the sugar still retained its sweet taste; but it could no longer be crystallized.

In general diabetic urine does not yield sugar in regular crystals. When the urine is cautiously evaporated and set aside, the sugar is deposited in small irregular grains, mixed with the usual constituents of urine. If we dry this sugar between folds of blotting paper, and then digest it repeatedly in cold alcohol as long as the liquid continues to acquire any colour, and finally dissolve it in water and crystallize it again, we obtain the sugar in small sphericles of a white colour, and composed of a congeries of needles radiating from a centre. It resembles sugar of grapes in its appearance, and Chevreul affirms that it possesses all the characters of that sugar. If this be true, it cannot be doubted that the diabetic sugar which formed regular crystals constitutes a different species. It has been ascertained that diabetic sugar possesses the capability of undergoing the vinous fermentation, and producing spirits precisely like common sugar and sugar of grapes.

2. Dropsy. — In cases of dropsy the urine is often loaded with the serum of the blood. It often coagulates when heated, or at any rate when mixed with an acid.

In jaundice the urine has an orange-yellow colour, and communicates the same tint to linen. Muriatic acid renders such urine green, and thus detects the presence of picromel.

In inflammatory diseases the urine is scanty, high coloured, and acrid. It deposits no sediment on standing, but is copiously precipitated by corrosive sublimate. About the end of inflammatory diseases the urine becomes copious, and deposits a pink-coloured sediment.

In hysteria the urine is usually limpid and colourless. It is deficient in urea, but contains a considerable quantity of the phosphates.

Blue urine, black urine, and white urine, have been occasionally observed.

3. Deposits from Urine. — The urine being a liquid secreted from the blood for the purpose of being thrown out of the body, and the intention of the secretion being obviously to keep the blood as nearly as possible in the same state, it is clear that it will undergo an alteration whenever the digestive organs are deranged. That this is the case every person must perceive who pays any attention to the secretion. In cases of perfect health the urine deposits no sediment. But when the digestive organs have been deranged by excess either in drink or food, the urine, though limpid when first voided, speedily becomes turbid, and deposits a copious sediment. These derangements are in general but momentary, and, unless the cause be persisted in, do not lead to any material injury to the system. But in cases of habitual intemperance, and also from other causes that cannot be always appreciated, the nature of the urine sometimes becomes permanently altered. In such cases solid matter is deposited in the kidney (or sometimes in the bladder), which, increasing in size, becomes a calculus, and gives origin to one of the most deplorable diseases to which mankind is liable.

When the urine becomes acid, uric acid is precipitated. This gives occasion to the formation of uric acid calculi, the most common species of these concretions. When the urine becomes alkaline, the quantity of earthy phosphates in it speedily increases. Hence phosphate of lime, and sometimes phosphate of magnesia, are apt to be deposited. This gives occasion to two other species of calculi, those composed of phosphate of lime, and those composed of a mixture of phosphate of lime and phosphate of magnesia, or of triple phosphate as it is usually termed.

There occur two other species of calculi, the origin of which it is not so easy to explain. One of these is oxalate of lime, or mulberry calculus as it is termed in consequence of some resemblance which such calculi have to a mulberry. The other, which is very uncommon, is known by the name of cystic oxide.

Uric acid calculi have usually a brown colour, and are sometimes smooth and polished on the surface, but much more frequently covered with little tubercles. They are composed of concentric coats indicating the. period of their formation. When in powder it dissolves easily in the fixed alkaline leys, from which it is precipitated in white powder by all the acids. It is insoluble in water.

Sometimes the uric acid is combined with ammonia, constituting urate of ammonia calculi. They have a good deal of the appearance of clay. They are rather uncommon; generally exist only in the urinary bladder of very young persons, and are productive of a very great degree of irritation.

Phosphate of lime calculi have a pale-brown colour, sometimes almost white, and their surface is so smooth as to appear polished. They are composed of very regular concentric laminae, rather thicker than those of uric acid calculi, and adhering to each other so slightly as to separate with ease from each other. When in powder this calculus dissolves easily, without effervescence, in nitric or muriatic acid. Before the blowpipe it may be fused, though an intense heat is necessary. The constitution of the phosphate of lime in calculi is different from that of apatite or native phosphate; the former being composed of an atom of acid and an atom of lime, while the latter consists of an atom of acid united to an atom and a half of lime.

Calculi composed of the triple phosphates are white, and resemble chalk. Sometimes they are smooth, and have a kind of silky lustre, and appear evidently composed of small prismatic crystals. These calculi are mixtures of two different salts, which occur in unequal quantities in different calculi. 1. Ammonia-phosphate of magnesia, a tasteless insoluble white matter, which is frequently crystallized in small prisms. 2. Phosphate of lime. These two salts are sometimes mixed with uric acid. The first two salts, when mixed in the requisite proportion, have the property of fusing before the blowpipe; hence the chalky [7:6:502] calculus is often distinguished by the name of fusible calculus. In some rare cases calculi occur composed very nearly of ammonia-phosphate of magnesia, or at least containing a much greater proportion of that salt than of phosphate of lime.

When acetic acid is poured upon fusible calculus previously reduced to powder, the ammonia-phosphate of magnesia is dissolved, and may be again thrown down unaltered from the filtered solution by the addition of carbonate of ammonia. Muriatic acid will dissolve the phosphate of lime, which escaped the action of the acetic acid; and it may be thrown down unaltered by caustic ammonia. Should the calculus contain also any uric acid, it will remain undissolved after the action of the acids, but may be readily dissolved by potash ley, and afterwards thrown down by acetic acid.

The mulberry calculus consists of oxalate of lime mixed with a little phosphate of lime and some uric acid. It is a hard calculus, commonly of a dark-brown colour, as if tinged with blood, and having an irregular and tuberculated structure. These calculi are seldom of a large size, or when they are, the nucleus alone consists of oxalate of lime, while the outer portion is sometimes uric acid, but more frequently fusible calculus.

Sometimes oxalate of lime calculi are remarkably smooth and pale coloured. They arc then known by the name of hemp seed calculi, and would appear to have their origin in the kidneys.

Cystic oxide calculi are very rare, not above ten or twelve having been hitherto observed. They are small and oval shaped, have a light-yellow colour, are translucent, and not composed of concentric laminae like the other calculi. They have a peculiar glistening lustre, like that of a body having a high refractive density. Before the blowpipe this calculus gives out a peculiarly fetid smell, quite different from that given out by uric acid, and not resembling prussic acid.

It dissolves, and combines equally with acids and alkalies, and crystallizes with both. It is precipitated from nitric acid by alcohol. It does not become red when treated with nitric acid. It produces no change on vegetable blues. It is insoluble in water, alcohol, and ether. When distilled it yields carbonate of ammonia and a heavy fetid oil, and leaves a very small, black, spongy coal, consisting chiefly of phosphate of lime. It has been subjected to a chemical analysis by Dr Prout, who found it composed of
[table]

This is equivalent to
[table]

Hence the atomic weight is fifteen, or a multiple of that number.

It is a very common thing for a calculus, when of considerable size, to be composed of various substances alternating in layers. In such cases uric acid pretty frequently constitutes the nucleus, sometimes oxalate of lime, and sometimes phosphate of lime. Very few calculi occur having a nucleus of fusible calculus; but this matter is a very frequent portion of large calculi, and generally constitutes the outermost layer. It is remarkable, that when the constitution of calculous patients is broken up by dis ease, the urine usually becomes alkaline, and great quantities of triple phosphate, or of fusible phosphate, are deposited; hence when calculi are extracted from the bladders of such persons after death, the outermost layer is very frequently a deposit of the chalky matter which constitutes the substance of fusible calculus.

CHAP. IX. OF THE SKIN.

The skin is a strong thick covering which envelopes the whole external surface of animals. It consists always of two layers, namely, the epidermis or scarf-shin, which is on the outside, and destitute of feeling, and when any portion of it is rubbed off it is soon replaced; and the cutis, or true skin, which is much thicker, and composed of a great many fibres closely interwoven and disposed in different directions. Anatomists mention a third substance placed between the cuticle and the cutis, to which they have given the name of rete mucosum.

The epidermis is easily separated from the cutis by maceration in hot water. It possesses considerable elasticity. It is insoluble in water and alcohol. The fixed alkalies dissolve it completely; as does lime also, though slowly. Sulphuric and muriatic acids act upon it very slowly, but nitric acid makes it yellow immediately, deprives it of its elasticity, and makes it fall to pieces. It consists chiefly of coagulated or indurated albumen. The following table exhibits the constituents of the epidermis of the foot, as determined by John.
[table]

The cutis or true skin is a thick, dense membrane, composed of interwoven fibres. When sufficiently macerated in cold water, most of the foreign matter, such as blood, mucus, &c. with which it is contaminated, is separated, When thus purified, it dissolves in concentrated alkaline leys. Weak acids soften it, render it transparent, and at last dissolve it. When digested in nitric acid it is partially converted into oxalic acid, while azotic gas is disengaged. Hydrocyanic acid is given out at the same time. When heated it contracts, and then swells, exhales a fetid odour, and after burning leaves a dense charcoal difficult to incinerate. When long boiled in water it dissolves, and is converted into gelatine or glue.

Of Gelatine.

When the solution of the skins of animals in water is sufficiently concentrated, it is converted, on cooling, into a transparent jelly. When this jelly is dried it becomes hard, semitransparent, and .breaks with a glassy fracture. When pure it is white; but glue, from overheating, has almost always a yellow colour. Its taste is insipid, and it has no smell.

When thrown into water it swells very much, but does not dissolve; yet it is converted into the same transparent tremulous jelly from which it was originally hardened. When heat is applied it melts, and becomes what in common language is known by the name of glue, and is in common use for fastening pieces of wood to each other. A very small quantity of dry gelatine converts a considerable quantity of water into a jelly. One part of gelatine from [7:6:503] isinglass dissolved in a hundred parts of hot water totally gelatinizes on cooling.

Gelatine, while dry, may be kept for any length of time without undergoing alteration; but when dissolved in water, or in the gelatinous state, it very soon putrefies.

When dry gelatine is exposed to heat it whitens, curls up like horn, then blackens, and is gradually consumed to a coal. It is by no means very combustible. When distilled in a retort it gives out combustible gases, while carbonate of ammonia sublimes, and there pass over into the receiver a light-brown watery liquid, and a dark-coloured oily matter of the consistence of tar. There remains in the retort a shining charcoal, of very difficult incineration.

Acids dissolve gelatine with facility, even when diluted, especially if they be assisted by heat; nor do they seem to decompose or alter it, provided they be dilute. From this we must except nitric acid, which occasions the evolution of azotic gas and deutoxide of azote. A quantity of oxalic and of malic acids is formed, and an oily matter appears on the surface of the liquid.

Muriatic acid dissolves gelatine with great ease. The solution has a brown colour,'and always continues strongly acid, though it has dissolved as much gelatine as it can take up.

When a current of chlorine gas is passed through an aqueous solution of gelatine, a white solid matter collects on the surface, and whitish filaments swim through the liquid.

Alkalies dissolve gelatine with facility, especially when assisted by heat, but the solution does not possess the properties of soap.

It is insoluble in alcohol (unless when very dilute), ether, fixed and volatile oils. When a solution of tannin is dropt into an aqueous solution of gelatine, a copious white precipitate falls, which gradually forms an elastic adhesive mass, not unlike vegetable gluten. This precipitate is a compound of gelatine and tannin. It soon dries in the open air, and forms a brittle resinous-like substance, insoluble in water, capable of resisting many chemical re-agents, and not susceptible of putrefaction. It resembles over-tanned leather. Leather is a combination of tannin and gelatine, or rather of tannin and the skin of animals. When gelatine is in the gelatinous state, it does not combine with or precipitate tannin. The tannate of gelatine is soluble in an aqueous solution of gelatine.

Tannin, or the infusion of nutgalls, is one of the most delicate tests for gelatine. It is not, however, free from ambiguity, because albumen is precipitated by tannin as well as gelatine. The same remark applies likewise to fibrin and the colouring matter of blood, which indeed might almost be considered as varieties of albumen. But if a liquid which is not precipitated by a solution of corrosive sublimate be precipitated by tannin, we may then be certain that it contains gelatine.

The other characteristic property of gelatine is its assuming the gelatinous form when a sufficiently concentrated aqueous solution of it is allowed to cool.

Gelatine has been subjected to a chemical analysis by Gay-Lussac and Thenard, who found its constituents as follows:
[table]

These numbers approach considerably to
[table]

Hence 10∙875, or a multiple of it, is probably the atomic weight of gelatine.

CHAP . X.—OF THE MUSCLES.

The muscular parts of animals are known in common language by the name of flesh. They constitute the parts by the contractions of which living beings arc put in motion.

Muscular flesh is composed of a great number of fibres or threads, commonly of a reddish or whitish colour. When these fibres are freed as much as possible from the bloodvessels, nerves, blood, fat, and other foreign matter with which they arc mixed, they consist chiefly of fibrin. The following table exhibits the result of an analysis of a portion of muscle thus purified by Berzelius.

1. Solid Matters.
[table]

2. Liquid Bodies.
[table]

Considerable variety occurs in the appearance, and even the chemical properties, of the muscles of different animals; but hitherto the subject has been very imperfectly investigated.

Of Ozmazome.

Ozmazome, so called from its smell, and the mode of obtaining it, is intimately connected with the muscles of animals, and is probably nothing else than fibrin altered in its nature by the heat applied. It may be obtained by the following process:

Divide the muscle of beef into small fragments, and leave it in contact with twice or thrice its weight of cold water for an hour or two, taking care to squeeze it occasionally. Decant off the first portion of water, and add an additional portion. Repeat the digestion a third time. These portions of water dissolve the salts, the albumen, and the ozmazome. Mix them all together, and evaporate them in a porcelain vessel till the whole albumen has coagulated and separated. Then filter the liquid, which will be reduced to a small quantity, and be of a deep colour. Evaporate it in a very gentle heat to the consistency of a syrup, and digest it in alcohol. The ozmazome will be dissolved, while the salts will be left behind. If we evaporate off the alcohol, the ozmazome will remain behind in a state of tolerable purity.

Its colour is brownish yellow, and it has the taste and smell of broth, or rather of beef-tea. It is soluble both in water and in alcohol. When the aqueous solution is heated, the ozmazome does not coagulate; nor does [7:6:504] it gelatinize when the hot concentrated solution is allowed to cool. When the water is driven off the ozmazome remains unchanged in the state of a brown-coloured matter.

The aqueous solution of ozmazome is precipitated by infusion of nutgalls, nitrate of mercury, and acetate and nitrate of lead. When ozmazome is heated, it melts, swells, and is decomposed, giving out carbonate of ammonia, and leaving a bulky charcoal, which contains some carbonate of soda.

A substance very similar to ozmazome is obtained when the muscles of animals are decomposed by the action of concentrated sulphuric acid. It is reddish, and tastes weakly bitter, like over-roasted meat. It is very soluble in water and alcohol, and is slightly precipitated by acetate of lead and infusion of nutgalls.

CHAP . XI. OF THE BRAIN AND NERVES.

The brain is well known to be the organ of sensation, and even of motion; for it communicates with every part of the body which has any function to perform by means of the nerves; and when the nerve leading to any part is surrounded with a ligature, that part loses its sensibility, and the power of performing its proper functions, till the ligature be withdrawn.

The brain consists of two substances, which differ from each other somewhat in colour, but which in other respects seem to be of the same nature. The outermost of these, from some small resemblance which it has to the colour of wood ashes, is called the cineritious part; while the innermost part is called the medullary part. Brain has a soft feel, not unlike soap. Its texture appears to be very close; its specific gravity is greater than that of water. When the contact of air is prevented, brain remains a very long time without undergoing putrefaction; but when the free admission of air is allowed, it putrefies with great rapidity.

It is insoluble in water; but when triturated with that liquid in a mortar, it forms a whitish-coloured emulsion, which appears homogeneous, may be passed through a filter, and does not allow the matter of brain to precipitate when left at rest. When this emulsion is heated to 145°, a white coagulum is formed. The addition of a great quantity of water likewise causes a coagulum to appear, which floats on the surface; but the water still retains a milky colour. Sulphuric and nitric acids, when dropt into the emulsion, occasion a white coagulum to separate. The same effect is produced by alcohol. This coagulum possesses properties very similar to those of albumen, of which it is probably merely a modification. When dried it becomes translucent, and breaks with a vitreous fracture.

When nitric acid is digested on brain, ammonia and oxalic acid are formed. When brain is kept for a sufficient length of time exposed to the heat of a vapour-bath, a quantity of water is driven off, and there remains a browncoloured matter, weighing from a fourth to a fifth of the original quantity of brain employed. Alcohol being repeatedly boiled upon this residuum, dissolves about five eighths of the whole. When the alcoholic solution cools, it deposits a yellowish-white substance, composed of brilliant plates. When this matter is kneaded between the fingers, it assumes the appearance of a ductile paste, which at 212° becomes soft, and, when the heat is still farther increased, blackens, exhales empyreumatic and ammoniacal fumes, and leaves behind it a charry matter. Pure concentrated potash ley dissolves brain, disengaging a great quantity of ammonia.

Brain, according to the analysis of Vauquelin, is composed as follows:
[table]

Dr John extracted the following substances from the brain of a calf:
[table]

CHAP . XII. OF BONES.

The bones are the most solid parts of animals. Their texture is sometimes compact, at other times cellular and porous, according to the situation of the bone. They are white, of a lamellar texture, and not flexible or softened by heat. Their specific gravity differs in different parts; that of adults’ teeth is 2∙2727; that of children’s teeth 2Ό833.

Bone consists essentially of two different substances, namely, a cartilaginous part, which has the shape and size of the bone, but is soft and elastic. When dried it becomes translucent, and of the consistence of horn; but by steeping it in water it becomes again soft and elastic, as at first. This substance may be obtained by digesting fresh bones in dilute muriatic or acetic acid. The earthy part of the bone is dissolved, and the cartilage remains behind. When cartilage is boiled in water, it gradually dissolves, and the solution, when sufficiently concentrated, gelatinizes on cooling; hence it would appear that cartilage approaches very closely to the nature of cutis. D’Arect has lately proposed this method of treating bones as an excellent one for converting their substance into a nutritive soup. He separates the earthy matter by dilute muriatic acid, and then dissolves the cartilage into a soup, which, when properly seasoned, is said to be both palatable and nutritive.

The other constituent of bones is the earthy matter which they contain, and to which they owe their solidity and strength. This earthy matter consists of three different salts, namely, phosphate of lime, carbonate of lime, and phosphate of magnesia. Berzelius found the constituents of ox bones as follows:
[table]

The constituents of human bones were found by the same chemist as follows:
[table]
[7:6:505]

Homs, nails, hoofs, and scales, are somewhat analogous to the cartilage of bones; and, like it, by boiling in water, ιnav at least in part be converted into jelly.

The membranes, both serous and mucous, and also the tendons, seem to approach the cutis in their nature. Ligaments are of a much stronger nature; but it is said that by long boiling they also may be converted into glue.

Bones arc liable to caries. In such diseases the phosphate of lime seems to be diminished, as appears from the foliowine analysis of a carious bone by Lassaiene:
[table]

We have now given an account of all the animal substances which can be introduced into this article, without anticipating what will require to be stated under Physiology. To that article we must refer those readers who wish for an account of those animal functions which admit of being elucidated by the application of chemical principles. There are, however, two animal substances upon which we have not yet touched, though they are of too much consequence to be omitted. These, namely, cantharidin and cochenilin, will constitute the subject of the two following chapters.

CHAP . XIII. OF CANTHARIDIN·.

By this name the substance in cantharides, or Spanish flies (meloe vesicatorius y ), which occasions a blister when applied to the skin, is distinguished. It may be obtained by the following process:

Boil cantharides in water till every thing soluble in that liquor be taken up. Concentrate the solution by evaporation, and when reduced to a thick syrup, boil it repeatedly in alcohol till that liquid ceases to act upon it. Evaporate the alcoholic solution gently to dryness, put the dry residue into a phial with sulphuric ether, and agitate the mixture for a considerable time. At first the ether will seem to have no effect on it; but after some hours it assumes a yellow colour. Decant it off, and allow it to evaporate spontaneously in the open air. It deposits small crystalline plates, mixed with a yellow matter. Alcohol takes up the yellow matter, but leaves the crystalline plates. These plates, when dried between folds of blotting paper, constitute cantharidin in a state of purity.

It has considerable lustre; it is insoluble in water and in cold alcohol. Boiling alcohol dissolves it, but lets it fall again in crystals as the solution cools. Ether dissolves it; but not very powerfully. Oils dissolve it readily. When applied to the skin it acts powerfully as a vesicatory. The solution of it in oils is equally efficacious.

CHAP . XIV.—OF COCHENILIN.

This name has been given by Dr John to the colouring matter of the cocheneah an insect that inhabits different species of cactus, and which is propagated in Mexicoand some other countries in order to be employed as a dyestuff. According to him the constituents of the cocheneal insect are as follows:
[table]

Cochenilin may be obtained pure by the following process: Digest the insect in alcohol as long as it commu∙ ∣ nicates a red colour to that liquid. When this solution is left to spontaneous evaporation, it lets fall a crystalline matter of a fine red colour. Dissolve these crystals in strong alcohol, and mix the solution with its own bulk of sulphuric ether. It becomes muddy, and after an interval of some days cochenilin is deposited at the bottom of the vessel in the form of a beautiful purplish-red powder.

Cochenilin has a granular appearance, as if it were com-: posed of crystals. It is not altered by exposure to the air. It melts at 122°. When the heat is increased it is decomposed, yielding inflammable air, a great deal of oil, and a little acidulous water, but no traces of ammonia.

It is very soluble in water, but the solution, though concentrated to the consistency of a syrup, does not crystallize. It has a fine carmine colour, and its colouring powers are very considerable. It is soluble also in alcohol, but the solubility diminishes as the strength of the alcohol increases. It is insoluble in ether. The weak acids dissolve it. No acid precipitates it when pure, yet they all produce a sensible change on the solution. At first it assumes a lively-red colour, which slowly changes into yellow. Concentrated sulphuric acid destroys and chars it. Muriatic acid decomposes it without charring it. Nitric acid acts with still greater rapidity, small needle-formed crystals being formed, which resemble oxalic acid, but do not precipitate lime water, even when mixed with ammonia.

The alkalies give the solution of cochenilin a violet colour, and gradually alter its nature when the colour becomes yellow. Lime water throws down a violet-coloured precipitate. Barytes and strontian occasion no precipitate, but produce a similar change of colour. Alumina has a strong affinity’ for cochenilin. When newly precipitated alumina is put into an aqueous solution of cochenilin, the liquid is deprived of its colour, and the alumina converted into a beautiful lake.

Acetate of lead throws down a violet-coloured precipitate from the aqueous solution of cochenilin. Nitrated suboxide of mercury produces a similar effect. The chloride of tin produces also a violet-coloured precipitate. Perchloride renders the solution scarlet, but occasions no precipitate.

Cochenilin is not precipitated by tannin or infusion of nutgalls.

From the experiments of Pelletier and Caventou, it appears that cochenilin is composed of carbon, hydrogen, and oxygen, and that it contains no azote whatever; but the atomic proportions of these constituents have not hitherto been determined. (l.) (Caloric, or Heat, will be treated of under the article Heat.)