# Essays Upon The Making Of Salt-Petre And Gun-Powder/Dr. Rush

New York Colony Committee of Safety, pages 8–16
​East-Indies, is made by art. I would not be understood to mean, that this salt is never found in a native state. It is sometimes found adhering to large rocks. It is likewise found in a native state under the arches of bridges and in vaults, or wine-cellars; but in these places it is found in such small quantities, that we are seldom at the pains of collecting it. It is found in a larger quantity in a native state in several plants; but of this I shall say more hereafter.
The manufactory of Salt-petre is now no longer confined to the East-Indies, but is carried on with equal advantages in many parts of Europe, particularly in Germany and France. I shall mention the several processes which are used for this purpose in each of these countries.
Crammer, a German chemist of considerable note recommends the following method of making Salt-petre, which says is practiced with great success in many parts of Germany. He orders lime rubbish of all kinds, garden, mould, and ashes to be mixed together, and moistened from time to time with urine, care being taken to stir them frequently. They should be all put into a small house, with a window towards the north-east. He does not direct, as some have supposed, to leave this house open towards the north-east, because the nitrous particles are brought from that quarter, but because the winds from the north-east in that country are generally accompanied with that temperature of the air, which is most agreeable to the formation of the nitre. In a month or two this ​mass will be so much impregnated with nitre, that one pound of it will yield two ounces of the salt. The King of Prussia was early sensible of the importance of a Salt-petre manufactory in his do- minions, and has therefore for this purpose always obliged his farmers to build their fences of com- mon earth, mixed with a quantity of straw and dung. These substances corrupt in the course of a few ears. The fences are then shaved, or wholly taken down, and afford a large quantity of Salt- petre. The sweeping of the streets of a single village in Hanover, afford all the Salt-petre that is used in the whole of that Electorate. Dr. Franklin, from whom I received this piece of of information, assured me that the manufactory of salt from the above materials was so simple that it was carried on entirely by an illiterate old man and his wife. The greatest part of the Salt-petre that comes from India is obtained nearly in the same manner. It is prepared entirely from the offals of the city of Patna. Mr. La Roux, of the academy of Rouen, informed me, that the following receipt had been found to answer very well in many parts of France for the manufactory of this salt : it is taken from Glauber, a German Chemist. I shall deliver it in his own words: "I will shew a way to such as have no inhe- ritance left them from their parents, nor have any ​ [ 10 ] thing to come to them by marriage, by what means they may without labour or trouble, get a trea- sure for their children. "First, Let such a one take care to have some shed or hovel made, to join to that side of his dwelling, that lies in the middle betwixt the north and east part of heaven, or forge other more convenient place, so as to admit the sun and air to it, but to keep off the rain. Under this pent-house or hovel, let him dig a large pit, and with the earth he digs out, let him make banks round the pit's mouth, so that it may keep the rain off on every side. This done, let him each day in every year, or whensoever he can conveniently, carry and throw into that pit these following matters, so long till his necessity forceth him to dig all out again, and see how much treasure he has got, even while he slept. Now these matters are all sharp and bitter herbs, growing in by-places amongst bushes, and on the way side, and such as beasts feed not on, as esula, cucuta or hemlock, henbane, fumatory, the thick stalks of tobacco, that are thrown away in those places, where it is planted, the hard stalks of colwort, which the beasts eat not of, and likewise all those things they leave in their troughs; likewise, fir-tops or apples if you have them at hand; also the leaves that fall from the trees in autumn are to be gathered; also pigeons dung, hens dung, birds and hens feathers; and ashes which women generally their lces with, and other ashes that is not fit for that use; as also fuel out of which the lee is already extracted; the soot of chimneys, hogs hair, and the horns of oxen and cows, and the bones the dogs eat not of. All these ​ [ 11 ] these matters may be thrown into this pit, and that he may the sooner fill it, he may gather as much as he can from all the bordering places, and throw it therein, so that in one or two years time he may with all these things fill up his pit : Mean while he must pour into the pit the urine gathered in his house, and that he may have enough, hee must get ass much as he can from his neighbours, so as to keep the things thrown into the pit in continual moisture, whereby they may the sooner putrify. In want of urine common water may be taken ; if sea-water or other salt water can be had, it will be better. Also the brine of fishes pickle, and the salting or salt-water that flesh is macerated (or pickled in) are of good use; also the blood of oxen, cows, calves, sheep, which you may easily have at the butcher's; all these things, putrifying together, do put on the nature and property of Salt-petre.
"If now all these matters in your full pit, shall have well putrified, then cease from pouring on any more moisture, and all the things are to be left so long till they are dried; then if you need money, let a Salt-petre maker be sought for, and bargain with him about the price of drawing off your Salt-petre by water, of making it and selling it. This done cast the remaining earth into a pit, together with the remaining lixivium, that shot not into NItre, and there leave it for a year or two, and moisten it sometimes with urine, or if you have not this, with common water. The earth will again yield Salt-petre, but not above half so much as at first."
But ​ [ 12 ] But the greatest quantity of Salt-petre that is consumed in France is prepared in Paris from the ruins of old stone building, pigeon-houses, stables, and all such putrid masses of vegetable or animal matters as have been long covered. To these a quantity of lime or ashes is added, which is laid to evolve the Salt from the said ingredients. Nitre, besides being obtained by the artificial process we have described, may be obtained in a considerable quantity in a native state from certain plants. The Tobacco is strongly impregnated with it. Every one that has taken particular notice of the stalks of Tobacco that has been well cured, when burning, must have observed a deflagration, or flashing exactly similar to that exhibited by Salt-petre when thrown upon coals. This phaenomenon, after I had frequently for many years observed, at length induced me, at a season of leisure, to attempt making Nitre out of tobacco, which I did, and own it was with no small confidence of success, as I know of no substance but nitrous salts which deflagrated in that peculiar manner. I made therefore a strong decoction of tobacco stalks, which by a number of experiments, I found replete with two kinds of nitrous salts, viz. nitrous ammonia and nitrous selenites, the same which are contained in the common mother ​ [ 13 ] mother lee of Nitre. In short, notwithstanding I wasted a considerable part of the decoction by ac- cidents and experiments, out of half a pound avoirdupois of dry tobacco stalks, I obtained (by adding pure fixed vegetable alkali, and disengaging the volatile alkali and earth) about an ounce of true Salt-petre : which however was brown by reasons of the oily parts of the stalks. Thus far I proceeded that time, but for want of leisure, have not as yet proceeded any farther. I beg leave however to recommend it to others, who may think it worth their while, to labour for an improvement of this hint towards a Salt-petre manufactory; and I would particularly recommend it to the tobacco colonies, to consider whether it be not an object worthy of their serious attention for I own I am so sanguine as to believe, that, by proper management, they might even make Salt-petre a staple commodity. The impurity of the Nitre I made was undoubtedly owing to the incompleteness of the putrefaction, which proceeds to no great length in the curing of it; but if under such circumstances eight ounces of stalks will afford an ounce of impure Nitre, there seems reason to believe that, if the putrefaction were to be completed in a bed of mould, till the tobacco was reduced to earth, and proper substances mixed therewith during the progress of putrefaction, to fix the nitrous acid as it forms, a lixivium drawn from such mould would yield a much larger quantity (with respect to the quantity of tobacco) of much purer Nitre, and probably much more than any other substance known. Were I therefore
B ​ [ 14 ] therefore a tobacco, plater, I would certainly try what might be done with a bed of mould made of refuse tobacco, and doubt not but it would fully answer my expectations. However, that might prove these hasty and perhaps seasonable hints are offered to the consideration of his countrymen, by a sincere and faithful friend to America. Those plants which contain Salt-Petre always sparkle when they are thrown into the fire. But there is another less equivocal method of knowing whether a plant contains any quantity of this Salt. Bruise the plant well and press the juice from it. Put this juice into an earthen pot, and place it in a cool cellar, first pouring a little sweet oil upon the surface of it to prevent its becoming mouldy. If the plant contains any Nitree, you will find it in the form of crystals on the sides of the vessel in six weeks or two months. The method of extracting the Salt-petre is nearly the same whatever ingredients we may employ for making it. The ingredients are put into tubs, barrels, or hogsheads, perforated at their bottoms. Rain, river, or very pure spring water, is poured upon them, which gradually dissolves all the salt they contain, and conveys it drop by drop into vessels provided to receive it. The nitre in this state contains a large quantity of common salt. Before I explain in what manner this salt is to be separated from the Nitre, it will be necessary to premise that bare evaporation, by boiling or otherways, will crystalize common salt, but that cold and rest are necessary to crystalize Nitre. The lee, (if I may so call it) made from the materials ​ [ 15 ] terials which yield Nitre, is put into a large copper vessel, and is gradually boiled away till crystals of common salt begin to form in it. These are taken out with a large laddle as fast as they form and thrown into a large basket which stands directly over the vessel in which liquor is boiling. When no more crystals of common salt can be found, the liquor is taken off the fire, and emptied into a number of copper-pans, in a cellar, in which it soon shoots into crystals of Salt-petre. The salt has now undergone its degree of purification. As a quantity of common salt still adheres to the crystals of Nitre, it is necessary to dissolve them in pure water, and boil them in the manner we laid before. A much less quantity of common salt is obtained now than formerly. The Nitre, after its second crystallization, is used chiefly for the purposes of medicine and curing provisions. But there is a third degree of purification necessary, before all the common salt can be completely separated from it. It is carried on in the same manner as the former ones were. The salt-Petre is now in its highest state of purity, in which state only it is used for the manufactory of GunPowder. The liquor which will not crystalize may be used for making Magnesia. I cannot conclude this Memoir without observing that the climate and productions of the middle and northern colonies of America, render them extremely proper for the manufactory of Salt-Petre, and the success which has attended several experiments in that way, give us reason to believe that it may be carried on in this country, with as
B 2 ​ [ 16 ] great advantage as in France, Germany, or the East-Indies.
METHOD OF MAKING SALT-PETRE AT HANOVER, 1766.
THE Salt-Petre works are within two miles of the town---they consist of a house that had probably been an old wooden barn, it had an earthen floor---on one side within, stood a row of casks open at top, filled with earth, and under each cask a tub to receive what water passed thro' the earth in the casks--- on the other side was an iron kettle set in brick work, which might boil at once perhaps two or three barrels of water---at the end farthest from the fire place, the floor was dug deeper about four feet; in this part as a cooler place, there were tubs of the boiled liquor set to crystalize---the ground belonging to the house, perhaps an acre and a half, was filled with what we should call mud walls, they were about three feet thick at bottom, and tapered up to one foot at top, heighth about five feet--- these are placed so near each other, that there is only room for a wheel-barrow to pass between, they are composed of street dirt and the rubbish of old buildings, such as plaister, morter, &c.---they are exposed to the sun, wind, and rain. Four persons were all the family who managed these works
* ↑ The north-east winds in North-America, are generally accompanied with moisture, which render them improper for the formation of Salt-petre. The house which contains our Salt-petre materials, should therefore, in this country, be exposed to the north-west winds.
* ↑ The earth under the floor of old stables is a plentiful source of Salt-petre. When this earth consists chiefly of clay, a quantity of sand or gravel should be added to it. The gravel or sand acts mechanically, by dividing the clay in such a manner as to suffer the water which is poured on it, to pervade all its parts. All the composts which afford Salt-Petre, may be made to yield a fresh quantity of the salt by exposing them for some months to the air.