# The American Cyclopædia (1879)/Silver

Edition of 1879. See also Silver on Wikipedia; and the disclaimer.
​SILVER, one of the precious metals, distinguished by its whiteness, its brilliant lustre when polished, its malleability, and its indifference to atmospheric oxygen. It is one of the most widely distributed of metals. Since it occurs frequently in a native state (though never chemically pure, being invariably alloyed with gold or copper, and sometimes antimony, arsenic, bismuth, quicksilver, or iron), and is easily fusible, it naturally became known to mankind in the earliest ages. The alchemists called it Luna or Diana. The Greek name ἄργυρος is from ἀργός, white, and is the source of the Latin argentum. Silver is one of the first metals named in the Old Testament, being included among the enumerated riches of Abraham. At that period, as in later times, it was used as a medium of exchange and as a material in the arts. In Solomon's reign it is said to have been so abundant as to be nothing accounted of, and the king had made it to be as stones in Jerusalem. Among other ancient nations it was also abundant. Polybius says the tiles upon the roof of the temple at Ecbatana were of solid silver, and the beams and pillars of the temple were covered with plates of silver and gold. These metals were obtained from Nubia, Ethiopia, Attica, Epirus, and the distant countries of eastern Asia. The rich Spanish silver mines were developed at an early day, and furnished the main supply of the metal for Phœnicia, Carthage, and Rome. Pliny speaks of a mine opened by Hannibal, which supplied him with 300 lbs. of silver daily, and was worked by adits reaching a mile and a half into the mountain. This was at Guadalcanal, at the foot of the Sierra Morena, in the modern province of Seville. Pure silver, in its massive state, is the whitest of metals. It takes by burnishing a brilliant lustre, though inferior to that of its white alloys with copper. When granulated by falling molten into water, it acquires a rough but exceedingly beautiful surface. Reduced from the chloride in the humid way, it appears as a gray, spongy powder. It crystallizes in cubes and octahedrons when allowed to cool from the molten condition or precipitated from solution for instance, by copper or zinc. Sometimes it is precipitated black by the galvanic current or by zinc. In hardness and strength it is superior to gold and inferior to copper; a slight alloy of copper hardens and strengthens it. In malleability and ductility it is inferior to gold only. (See Metal.) Leaves less than 1/100,000 of an inch thick can be obtained by beating, and wires may be drawn out of extreme tenuity. Its chemical symbol is Ag, its equivalent 108. According to G. Rose, the specific gravity of cast silver is 10.505, of pressed or hammered silver 10.566. Other authorities give for the former 10.474, and for the latter 10.510. Lengsdorf found the specific gravity of silver wire which had been repeatedly drawn to be 10.47 before heating and 10.43 afterward. The specific heat of silver is given by Regnault as 0.057. Its heat-conducting power is greater than that of any other metal, as is also its power of reflecting ​light and heat when highly polished; but its radiating capacity in the same condition is very small. By virtue of these properties vessels of silver are best adapted to retain the heat of liquids. It melts at a full red heat, about 1000° C. (1832° F.). It shrinks in cooling, and hence fills but imperfectly the moulds in which it is cast. At a very high temperature it is volatile. Melting silver mechanically absorbs 20 volumes of oxygen, which in solidifying it expels, sometimes with sufficient force to throw off particles of metal. Alloyed with 1 or 2 per cent. of copper or with gold, it apparently loses this property. Silver is oxidized neither by exposure at ordinary temperature to dry or moist air, nor by heating in air; but it burns to an oxide when melted upon charcoal in the oxyhydrogen flame, or when exposed to a galvanic current of great intensity, or to ozone. Chlorine, bromine, and iodine act upon it at ordinary temperatures. It has strong affinity for sulphur (with which it can be easily fused to a sulphide), and is hence readily tarnished by sulphuretted hydrogen, which is present in small quantities in the ordinary air of cities. To protect silver vessels not in use, they may be wrapped in paper saturated with wax, which keeps out the impure air, or in paper painted with white lead, which decomposes sulphuretted hydrogen. Articles of food, with the exception of eggs and salt, scarcely affect silver, and it is therefore a favorite material for table ware. The discoloration from eggs is due to sulphur; that from salt, to chlorine, which forms argentic chloride. This may be removed by rubbing with a linen rag moistened with aqua ammoniæ. The caustic alkalies in solution or fusion do not attack silver as they do platinum, and it is consequently employed for the evaporation of such solutions, and for crucibles in which minerals are fused with potassium or sodium hydrate. Silver foil is sometimes used in blowpipe analyses, for detecting sulphur and the sulphides of the metals. Melted with carbonaceous matter, silver forms a carburet, white like the metal. This is also formed when compounds of silver oxide are decomposed by organic acids.—Silver may be easily alloyed by melting with most metals. The alloys with base metals are in general not useful enough to counterbalance the cost of the silver. The alloy with copper, which in subordinate quantity enhances the valuable qualities of the silver, is an exception. The alloys with lead and zinc, serving an important purpose in metallurgy, will be mentioned further on. An alloy of 100 parts of aluminum with 5 of silver gives a handsome white malleable compound, susceptible of high polish. A small quantity of iron, chromium, cobalt, or nickel imparts great hardness to silver. Steel may be made to retain about 1/500 of its weight of silver, which is said to improve its quality; the alloy is called silver-steel. Combined with mercury, silver forms a most brilliant amalgam for mirrors. An alloy of 20 to 30 parts of silver with 30 of nickel and 50 of copper is said to be equal in all respects to the ordinary standard silver, which is 9 parts of silver with 1 of copper. Small coins have been made in Switzerland of an alloy of silver and copper with 10 per cent. nickel. Two parts zinc and one part silver give a ductile, white, fine-grained alloy. Three parts of silver to one of tin give a hard, and one part of silver to two of tin a soft alloy. Bismuth, antimony, and arsenic yield brittle alloys. The alloys of silver and copper are the most important of all, being used both in coinage and in the arts. The copper alloy is harder than pure silver, takes a finer polish, and wears better; and the white color of silver may be retained if the contents of copper do not exceed a certain proportion, while even those alloys containing a larger proportion of copper may be so treated by “pickling” in acid as to deprive them of copper on the surface, and thus restore their silver-white color. The standard silver for coinage, on the continent of Europe and in the United States, is a compound of 9 parts of silver to 1 of copper; in England, of 37 silver to 3 copper. For plate the legal fineness varies in different countries, or is, as in the United States, left to the choice of the manufacturer. In North Germany the usual fineness is inferior to that of coin.—Silver does not dissolve in any hydrated acids by taking the place of the hydro- gen; on the contrary, hydrogen displaces it from the solutions of its salts and precipitates it in metallic form. Concentrated sulphuric acid oxidizes silver at boiling heat, forming argentic sulphate and sulphurous acid. Nitric acid, even when diluted with an equal bulk of water, acts rapidly upon silver, and at high temperature with great violence, argentic nitrate and nitric oxide being formed. A solution of chromic acid changes silver to a red argentic chromate. Muriatic acid, even at a high temperature, has little effect upon silver. Argentic oxide combines at high temperatures with silicic acid; hence, silver heated or melted with glass or other silicious compounds becomes oxidized and colors the mass yellow. All of the more easily oxidizable metals and many compounds susceptible of higher oxidation (so-called deoxidizing substances), as well as many organic substances, precipitate silver from solution. Silver forms three oxides: a suboxide, Ag$_4$O; argentic oxide, Ag$_2$O; and a peroxide (probably Ag$_2$O$_2$), which does not combine with acids. The second of these is of special interest as the basis of the salts of the metal. It is separated from the nitrate, or any soluble silver salt, by adding an alkaline solution, as a brown hydrated oxide, which parts with its water at 60° C. (140° F.), and with its oxygen at a red heat. Its solution in ammonia deposits on exposure to the air a black micaceous powder supposed to be a compound of silver oxide and ammonia (Ag$_2$O, H$_3$N), or amidide of silver (AgH$_2$N), ​or nitride of silver (Ag$_3$N). It is terribly explosive, and is hence called fulminating silver (Berthollet's). This most dangerous compound may also be unintentionally produced by precipitating an ammoniacal solution of argentic nitrate by the addition of caustic potash. The chlorate of this oxide is likewise very explosive, as is also the fulminate proper (Brugnatelii's). (See Explosives.) The sulphate is formed by treatment of the metal at a high temperature with concentrated sulphuric acid. Upon this reaction is based one method of separating silver and gold. (See Gold.) The nitrate (AgNO$_3$) is the most important salt of silver. (See Nitrates, vol. xii., p. 463.) It is employed in the preparation of other compounds of silver, the most important of which is the chloride, produced by adding to the nitrate solution chlorine or a soluble chloride, such as common salt. It is a dense white flocculent precipitate, which under exposure to light turns first violet, then black, probably by partial reduction to subchloride. Chlorine restores the white color. The chloride is slightly soluble in boiling concentrated muriatic acid, more readily in strong solutions of chlorides, ammonia, alkaline cyanides, and hyposulphites; insoluble in water and dilute acids; scarcely affected by any oxygen acid, even concentrated sulphuric; reduced to metal by zinc, iron, copper, or any metal more oxidizable than silver, heated hydrogen, organic compounds containing hydrogen, alkalies and alkaline earths, and by heating upon charcoal before the blowpipe. The insolubility of the chloride in oxygen acids permits the precipitation of silver from solutions of almost all its salts by the addition of hydrochloric acid or of other chlorides, thus giving a convenient means of determining its presence or separating it from other metals. On the other hand, the solubility of the chloride in brine or sodium hyposulphite constitutes an important means of silver extraction by the humid method of metallurgy described below. This salt occurs in nature as an ore. It is used in photography, and its ammoniacal solution is employed to color mother-of-pearl. The bromide (AgBr) and the iodide (AgI) also occur in nature, the latter rarely. Their chemical relations are similar to those of the chloride, but the bromide is but slightly dissolved in dilute aqua ammoniæ, and the iodide scarcely at all. They likewise have the property of darkening by exposure to light. (See Photography.)—The Metallurgy of Silver. Silver is obtained partly from true silver ores, partly from other ores containing silver as an accidental or variable constituent. To the former class belongs the native metal, which is usually more or less alloyed with gold, and sometimes with other metals, as above remarked. The occurrence of gold and silver in variable natural alloy is so general that they may almost be said to constitute but one mineral species, ranging from silver with a slight trace of gold to gold with a slight trace of silver. Native silver is found in masses and in arborescent and filiform shapes in veins of quartz, calcite, &c., or as segregations accompanying other silver ores. The masses are sometimes crystalline, showing cubical and octahedral forms. Very pure silver occurs with the native copper at Lake Superior. The most famous masses of native silver, several of which exceeded 500 lbs., have been found at the mines of Kongsberg in Norway, of Freiberg, Schneeberg, and Johann-Georgenstadt in Saxony, and in the Bohemian, Hungarian, Peruvian, and Mexican mines. In the silver mines of Nevada, Idaho, and Utah it is not uncommon, though it has not been found in large masses. Silver amalgam occurs in small quantities in some European mines, and contains 26 to 35 per cent. of silver, the remainder being mercury. The variety known as arguerite, from Coquimbo in Chili, is an important ore in that region, and contains 43 to 63 per cent. of silver. The antimoniuret and the telluret of silver are comparatively rare. The most important silver ores are the chloride, the sulphide, and the combinations of sulphide of silver with other sulphides. The chloride of silver, or horn silver (AgCl), is a common ore in Chili, Peru, Mexico, and the western regions of the United States, particularly in certain districts of Nevada, and in the Owyhee district of Idaho. It has been met with in small quantities in many of the European mines. When pure, its composition is silver 75.2, chlorine 24.8. It has a waxy appearance, resinous lustre, and pearl-gray, greenish, whitish, or bluish color, turning brown in the air; hardness 1 to 1.5; sp. gr. 5.3 to 5.5. It occurs chiefly near the outcrops of argentiferous deposits as a product of the decomposition of other ores. In Chili and Peru, for instance, it is found in cubical crystals in the ferruginous gossan known as pecos and colorados. The bromide and iodide, which also occur in nature, closely resemble it, but are far more rare. The sulphide of silver (Ag$_2$S, silver glance, vitreous silver, or argentite), containing 87.1 silver and 12.9 sulphur, is, next to the native metal, the richest ore. It has a blackish lead-gray color, metallic lustre, and shining streak; H. 2 to 2.5 ; sp. gr. 7.196 to 7.365; is easily cut with a knife, and readily melts on charcoal before the blowpipe. It forms a considerable portion of the ores of the silver mines of Saxony, Bohemia, Hungary, Mexico, Peru, and the United States. It is commonly associated with other argentiferous minerals, and sometimes is finely disseminated through the gangue or the accompanying ores. The double sulphides of silver and antimony constitute a very valuable class of ores, of which the chief are: stephanite (Ag$_5$SbS$_4$), with 68.5 per cent. of silver and sometimes small quantities of iron, copper, and arsenic, having metallic lustre, iron-gray color, black powder, H. 2 to 2.5, sp. gr. 6 to 6.27, occurring in Saxony, Bohemia, Hungary, Mexico, and ​Nevada, particularly in the Comstock lode; miargyrite (AgSbS$_2$), with 36.9 silver, steel-gray to iron-black, metallic lustre, dark cherry-red powder, H. 3, sp. gr. 5.2, occurring in Saxony, Spain, and Mexico; pyrargyrite (Ag$_3$SbS$_2$), dark ruby silver or antimonial silver blende, with 59 silver sometimes a little arsenic, black or by transmitted light deep red, H. 2 to 2.5, sp. gr. 5.759, occurring in Saxony, Baden, Cornwall, Norway, Mexico, South America, and Nevada; and polybasite (Ag$_9$SbS$_6$), with from 64 to more than 72 silver, the antimony being partly and sometimes wholly replaced by arsenic, and the silver partly by copper or to less extent iron and zinc, color iron-black, streak black, H. 2.5, sp. gr. 6.2, occurring in the Hartz, Saxony, Hungary, Mexico, and Nevada. Proustite, or light ruby silver (Ag$_3$AsS$_3$), similar to pyrargyrite, except that the color is lighter and the antimony is replaced with arsenic, occurs in the same localities, but more rarely; it contains 65.4 silver. Copper silver glance or stromeyerite (CuAgS), with 53 silver and 31 copper, iron-black, black shining powder, H. 2.75, sp. gr. 6.2, occurs in Silesia, Chili, and elsewhere. The foregoing are the principal true silver ores. The chief argentiferous ores of other metals are those of lead, copper, and zinc. Iron pyrites and arsenical pyrites, as well as bismuth, cobalt, and nickel ores, may be argentiferous, but it is usually by reason of finely disseminated silver ores throughout their mass. Galena is always more or less argentiferous. In the United States, the galena of the Appalachian range and of the Mississippi valley is usually poor in silver, while that of the Rocky mountains and the interior basin to the Sierra Nevada is highly argentiferous. Oxidized ores are usually poor in silver, but the carbonate, &c., occurring in the limestone of New Mexico, Utah, and the Eureka district, Nevada, are exceptions, being smelted in large quantities for lead and silver. The peculiar ore known as stetefeldtite, which occurs abundantly in Nevada, is an oxidized but massive mineral containing antimony and other base metals, and often very rich in silver. The variable mineral or class of minerals known as tetrahedrite (Fahlerz, argentiferous gray copper, freibergite, tennantite, hermesite) seems to be a combination of metallic sulphides with sulphides of antimony and arsenic, or a sulphide of antimony and copper, in which the antimony may be partly replaced by arsenic, and the copper by iron, zinc, silver, and even, as in freibergite, lead, or, as in hermesite, quicksilver. The percentage of silver varies from a mere trace to 32 per cent. Pure zinc blende is usually poor in silver, but is frequently found in intimate association with true silver ores or native silver, and particularly with argentiferous galena; and in some notable instances the blende is richer than the galena.—The mechanical concentration of silver ores by water is attended with heavy loss, by reason of their usual association with base ores of nearly the same specific gravity, and their property of cleaving when crushed into fine scales and splinters or dust, which are usually carried away by the current. The yield of silver ores is generally rated in this country in ounces troy to the ton of 2,000 lbs. avoirdupois or 29,167 oz. troy. About 1 per cent. of silver would be equivalent to 292 oz. to a ton. A yield of a little less than 3 oz. is represented by the decimal .0001 or .01 per cent. This small proportion will not pay for the mining and reduction of the ores; but where lead is produced containing .01 per cent. of silver, the latter can still be extracted and saved by refining processes. (See Lead.) The pig lead (variously called work lead, crude bullion, and base bullion) mainly produced from argentiferous galena, carries from 20 to 200 oz. of silver to the ton.—The methods of producing silver from ores and furnace products may be divided into three classes: smelting, amalgamation, and humid extraction. The smelting processes are mostly based upon the capacity of metallic lead, as well as its oxide and sulphate, to separate silver under fusion from its combinations, the liberated silver alloying itself with an excess of lead and accumulating in the metallic bath in the hearth of the furnace. The following chemical equations indicate the typical reactions of the lead smelting processes: Ag$_2$S + Pb + xPb = Ag$_2$,xPb + PbS; Ag$_2$S + PbO = AgPb + SO$_2$; Ag$_2$S + PbSO$_4$ = Ag$_2$Pb + 2SO$_2$. (See Metallurgy.) From the argentiferous lead thus produced the silver is obtained directly by an oxidizing fusion (cupellation), transforming the lead into litharge and leaving metallic silver upon the cupel; or the argentiferous lead is first submitted to treatment in a battery of melting kettles, in which at a low temperature a portion of the liquid mass crystallizes, while another portion, rich in silver, remains liquid; and the crystals being ladled from each kettle to the next, and there submitted to remelting and recrystallization, while the liquid is passed down the series in an opposite direction, the contents of silver are at last chiefly concentrated into a small quantity of so-called rich lead, which is then cupelled (the Pattinson process); or the silver is extracted from the molten lead by means of the superior affinity between silver and zinc, metallic zinc being added to the bath and the zinc-silver alloy rising to the surface and being skimmed off and submitted to further treatment by means of smelting, liquation, or distillation (the Parkes process, with the modifications of Cordurié, Flach, and others). In smelting argentiferous copper ores, the silver is often concentrated in a copper matte or black copper, which may then be smelted with lead, or treated in the humid way. The liquation of argentiferous copper consists in alloying it with a certain quantity of lead, and afterward heating the alloy above the melting point of lead, but below that of copper. The lead “sweats” out, carrying the silver with it, and leaving ​behind the spongy copper. This process has almost everywhere given way to humid methods. (See Copper, Lead, and Metallurgy.)—The method of amalgamation, invented in Mexico in 1557 by Bartolomé de Medina, led to the enormous production of silver there and in South America during the next 200 years, and has remained substantially in extensive use ever since. The Mexican, known as the patio process, is suited to ores which contain native silver or silver chloride (bromide, iodide) and sulphide, and are measurably free from other sulphides and from arsenides and antimoniurets. The ore is first crushed and then ground fine in arrastras. If gold is present, 50 or 60 per cent. of it may be saved by introducing silver or copper amalgam into the arrastra. Ores containing pyrites, antimony, or arsenic are incompletely roasted, to break up the combination of silver with these elements. The presence of silver sulphide does hot necessitate roasting as a preliminary for patio amalgamation. The fine paste from the arrastra is spread on the patio floor (of stone, calked boards, or asphaltum) in round heaps (tortas) about 0.3 metre high and 10 to 16 metres in diameter, containing each from 5,000 to 100,000 kilos; average, about 60 tons. The paste having stiffened by the evaporation of its water, from 2½ to 10 per cent. of impure salt is added, according to the contents of silver in the ore. This is intermixed with shovels and subsequently by the treading of mules or men, and occasionally by means of kneading machines, with travelling wheels, set up in the torta. After one or two days the magistral is added; this is copper vitriol and salt, or rich oxidized copper ores mixed with pyrites which has been roasted with salt, or simply copper pyrites which has been so roasted. The quantity of magistral required varies according to the season, the temperature, and the quantity of the ore; it usually ranges from ½ to 1 per cent. Its function is to cause certain reactions with the salt and the sulphide of silver and promote the formation of amalgam. Too much of it causes too high a temperature in the mass, particularly in winter; hence cold weather and poor ores require the smallest amount. After another treading, quicksilver is sprinkled over the torta by squeezing through a leather or canvas bag. The quantity used is six to seven times the weight of silver in the ore, sometimes much more. It is rarely added all at once; the usual practice is to give fresh quicksilver every alternate day, treading the mass for six to eight hours on each intervening day. The termination of amalgamation is observed by panning samples (see Gold) from the torta, and examining the amount and condition of the quicksilver and amalgam. The period required for the whole operation down to this point varies from 5 to 30 days; average, about 19 days. Various theories have been proposed concerning the chemical reactions of the patio. Too low a temperature stops the reactions, and may be remedied by more frequent treading or by additional magistral. The amalgam is collected in settlers, which are circular vats of wood or masonry, about 9 ft. in diameter and 8 ft. in depth, in which the mass, thinned with water, is stirred and allowed to deposit its heavy amalgam, while the lighter portion is drawn off. The amalgam, being concentrated still further, is at last collected in a leather or canvas bag, where it is freed by squeezing from free mercury, which passes through, carrying a little silver with it, while the mass remains in a coherent, plastic condition. The former is used again on the patio; the latter is moulded into 30 lb. blocks, piled on an iron plate, covered with a large iron bell, and heated by means of a charcoal fire around the bell. The mercury is vaporized, and (the joint at the edge of the bell being carefully luted) passes down through a pipe in the iron plate into a cistern of water. The bell furnace is less economical of fuel and mercury than muffle or retort furnaces; it loses 0.8 per cent, of mercury. The silver, found in solid masses when the bell is raised, is cast into ingots of 80 or 90 lbs. By the patio process the usual product of silver is 50 to 66 per cent. of that contained in the ore; the most docile ores, under favorable circumstances, have yielded 90 per cent. The loss of quicksilver is given by Kerl as 3 to 5 per cent. of the quantity used; earlier accounts make it considerably greater. This loss is due to the formation in the torta of soluble mercury dichloride (calomel), which is afterward washed away.—The cazo process, used in Mexico and Chili, is a hot amalgamation in kettles. The ore (in Mexico chloride, in Chili sulphide) is placed, in the form of a watery pulp, in a vat with copper bottom and wooden or stone sides. Here it is heated and stirred with salt and quicksilver, copper vitriol being added in the treatment of sulphides. The process is rapid and effects a tolerably complete extraction of silver, but involves great loss of quicksilver (2 to 2.5 times the weight of silver) when applied to sulphide ore. Silver ores free from sulphides of other metals are amalgamated at Guanajuato, Mexico, in arrastras, by simple grinding and mixing with quicksilver and water.—Pan amalgamation, called the Washoe process, consists in rubbing together in pans (usually of cast iron) the watery mixture of crushed ore (pulp) with quicksilver, with or without the addition of other chemicals. The simplest form of it may be thus described: The ore suitable for this process (usually containing silver sulphide or chloride and native silver, with little antimony, arsenic, base sulphides, in a gangue of quartz) is first crushed in a stamp mill, similar in most respects to that employed for gold-bearing quartz. (See Gold.) The screens which regulate the size of the crushed particles are of wire cloth with 40 to 60 meshes to the inch, or of Russia sheet iron, perforated with holes 1/40 to 1/24 in. in diameter. The pulp reduced to this fineness ​is ground and amalgamated in pans, of which there are numerous forms. The charge for a pan is 800 to 1,500 lbs.; the very large pans treating tailings which have been already ground fine, can take 3,000 to 4,500 lbs. To maintain a proper temperature, steam is introduced into the pulp or into a steam chamber under the bottom, and a wooden cover is usually kept on the pan. The pulp is generally ground for one or two hours; then the quicksilver is sprinkled in (usually 60 to 70 lbs. to a charge of 1,200 or 1,500 lbs.), and, the mullers being raised to avoid too much grinding, which would “flour” the mercury, stirring is continued for two or three hours longer, after which the pulp is diluted and drawn off into a settler. The modification of the Washoe process invented by Mr. Henry Janin, consisting in the use of large quantities of copper vitriol (blue stone) and salt, has proved very successful in the reduction of refractory ores not otherwise amalgamable. The quicksilver, charged with amalgam, is washed, skimmed, and strained through a canvas bag, which retains the amalgam. This is then distilled in cast-iron retorts, the mercury being collected under water, while the “retort bullion” remains behind. About one sixth of the charge retorted, or 200 lbs. of bullion from 1,200 lbs. of amalgam, is usually obtained from the retort, to be broken up, melted, and cast into ingots; it loses 2 to 3 per cent. in melting. The ingots are assayed, and their fineness in thousandths of gold and silver is stamped upon them. The coin value of the Comstock bullion is $1 75 to $2, one third of which is due to the gold it contains. The pulp escaping from the apparatus in which the amalgam is collected is called “tailings.” The tailings are often concentrated upon blankets or otherwise, or are simply allowed to settle in reservoirs, for reworking. The “slimes” or “slums” comprise that part of the ore which is crushed under the stamps to an impalpably fine condition, and escapes in the battery water without ever getting into the pans. Since many silver ores yield much fine powder in crushing, the slimes are often far richer than the tailings, the value of the latter being largely in the particles of quicksilver and amalgam which they contain. The chemistry of the Washoe process is summed up by Mr. Arnold Hague as follows: that the ore submitted to it consists chiefly of native gold, native silver, and argentiferous sulphurets, associated with varying portions of blende and galena; that the action of sodium chloride and copper sulphate in the pan produces copper chloride, while the presence of metallic iron causes the formation of copper dichloride; that both the chlorides of copper assist in the reduction of the ore by chloridizing the sulphurets of silver and decomposing the sulphurets of lead and zinc; that sulphate of copper enhances the amalgamating energy of mercury, by causing the formation of a small quantity of copper amalgam, and also tends to expel the lead; but that the quantities of chemical agents usually added in the Washoe process are too small to be effective, and that the principal agents in the reduction are in general mercury and the iron of the pan, aided by heat and friction. The essential condition in the amalgamation is the keeping of the mercury bright and pure, that it may come into direct contact with the iron and sulphide of silver. The consumption of mercury in the Washoe process may be considered chiefly a mechanical loss, and only to a limited extent a chemical one. The pan amalgamation of slimes and refractory ores, with the addition of large proportions of copper sulphate and salt, involves a greater loss of mercury.—Refractory ores, not suitable for “raw” amalgamation by the Washoe or the patio process, are treated in many localities by the Freiberg process, consisting in the chlorination of the ore by roasting with salt, and its subsequent amalgamation. At Freiberg in Saxony, where this method originated, it has been abandoned, the ores formerly amalgamated being now treated by smelting. But in districts where fuel is scarce and labor dear, and lead ores for smelting are not at hand (which is the case in many parts of Nevada, for instance), the Freiberg system is still successfully employed, though greatly modified as to apparatus. The ore is crushed in stamp mills, without water, and the fine powder is further dried, usually by spreading on the top of the arch or the dust chambers of the roasting furnace. Either in the battery, during crushing, or on the drying or the charging floor, 6 to 7 per cent. (for rich ores, up to 20 per cent.) of salt is mixed with the ore. The mixture is then roasted, to chloridize the silver; this was done abroad in reverberatory furnaces, which have been used in Colorado and Nevada also, but are now generally replaced in the west by Stetefeldt's showering furnace or Brückner's cylinder. From the roasting furnace the ore is conveyed to the pans, where it undergoes an amalgamation similar to that of the simple Washoe process, except that less grinding is necessary. The Freiberg amalgamation was performed in revolving wooden barrels, which are still employed at some places in the United States. Each apparatus has its partisans. A peculiar method of amalgamation pursued in Chili avoids the chloridizing roasting, substituting a humid chlorination by means of copper dichloride (Kröncke's process). It is highly praised, but not yet widely employed. The use for this purpose of copper chloride, which is of earlier origin, involves a loss of quicksilver as calomel.—The processes of humid extraction of silver are of two classes. Either the silver is converted into a soluble compound and separated by leaching and precipitation, or the baser metallic constituents of the ore are rendered soluble and removed by leaching, leaving an auriferous and argentiferous residuum for further treatment. The methods of the first class convert the silver ​into chloride or sulphate, the former by a chloridizing, the latter by an oxidizing roasting. The chloridizing roasting is essentially that of the Freiberg amalgamation process, and is effected by mixing salt with the charge. The silver chloride is extracted from the mass by lixiviation with hot brine (old Augustin process), cold brine (Hungarian improvement), sodium hyposulphite (Patera process), or calcium hyposulphite (Kiss process in Hungary and Russia, Hofmann in Mexico). The latter extracts also gold chloride if it is present, which brine will not do, unless it has been, as Patera recommends, impregnated with free chlorine gas. Experiments conducted at Wydotte, Mich., by Messrs. Courtis and Hahn, indicate the availability of other chlorides than common salt (particularly calcium chloride, or a solution obtained by treating common limestone with muriatic acid) as a solvent for the silver chloride. The novel and important results of these investigations are given in the “Transactions of the American Institute of Mining Engineers.” From its hyposulphite or chloride solution the silver is precipitated with metallic copper, as cement silver, which is washed, pressed, melted, and cast into bars. Ziervogel's method of extracting silver by roasting the sulphuretted ore to produce silver sulphate, leaching this with hot acidulated water, and precipitating with copper, is the simplest and cheapest of all; but it requires very skilful and delicate roasting, and ores comparatively free from lead, antimony, arsenic, and zinc. The three latter tend to cause volatilization of silver; the sulphide of antimony and lead cause a sintering of the roasting charge; copper dioxide, or too high a temperature in the furnace, leads to the formation of metallic silver, instead of the desired sulphate. Hence the application of this process is limited. Its best field is the treatment of the copper mattes of Mansfeld, containing 70 to 72 per cent. of copper, and 0.33 per cent. of silver. The so-called acid extraction is principally used upon cupriferous furnace products, which contain too much lead, antimony, arsenic, &c., to permit treatment by the Augustin or the Ziervogel method. In this process, the base metals are dissolved out by treatment with sulphuric or muriatic acid, and the residuum, containing gold and silver, is further reduced by smelting, or in rare instances by humid methods. For full discussions of all the foregoing processes, see Percy's “Metallurgy,” and Bruno Kerl's Metallhüttenkunde. The details of American practice, and critical comparisons of different American and foreign methods, are given in the reports of R. W. Raymond, United States commissioner of mining statistics, and in the “Transactions of the American Institute of Mining Engineers.”—The principal uses of silver have been mentioned already in this article; see also Coins, Galvanism (section on electrotyping), Mint, and Plated Ware. The real value of silver as compared to gold has varied in different ages from one eighth to less than one sixteenth; but the mint rates have often been arbitrarily established by government for the profit of the treasury, in spite of the market price of the metals. At present it is lower than at any previous period. The average ratio of value of silver to gold in the London market for the year ending Dec. 31, 1874, was 1 to 16.27. The following table shows the estimated product of silver at various periods in the present century:
Estimate of  W. P. Blake for 1867. :
| COUNTRIES. | Weight, lbs. troy. | Value, £ sterling. | Weight, lbs. troy. | Value, £ sterling. | Value, U. S. coin. | Weight, lbs. troy. | Value, U. S. coin. |
| Russian empire | 58,150 | £167,831 | 60,00 | £171,817 | $928,000 | 58,000 | $700,000 |
| Scandinavia | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ 141,000 | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$ 32,346  109,989    138,022    198,200    282,654    7,444  227,499 | 20,400 | 35,607 | 328,000 | 15,000 | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ 8,600,000 |
| Great Britain | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ 141,000 | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$ 32,346  109,989    138,022    198,200    282,654    7,444  227,499 | 48,500 | 160,000 | 1,120,000 | 60,500 | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ 8,600,000 |
| Hartz $\scriptstyle {\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}\,$ Prussia | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ 141,000 | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$ 32,346  109,989    138,022    198,200    282,654    7,444  227,499 | $\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$ 31,500  21,200 | $\scriptstyle {\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}\,$   138,022 | $\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$ 480,000  480,000 | 28,000  68,000 | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ 8,600,000 |
| Saxony | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ 141,000 | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$ 32,346  109,989    138,022    198,200    282,654    7,444  227,499 | 63,600 | 198,200 | 960,000 | 80,000 | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ 8,600,000 |
| Other German states | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ 141,000 | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$ 32,346  109,989    138,022    198,200    282,654    7,444  227,499 | 2,500 | | 48,000 | 2,500 | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ 8,600,000 |
| Austria | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ 141,000 | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$ 32,346  109,989    138,022    198,200    282,654    7,444  227,499 | 87,000 | 286,971 | 1,440,000 | 92,000 | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ 8,600,000 |
| France | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ 141,000 | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$ 32,346  109,989    138,022    198,200    282,654    7,444  227,499 | 5,000 | | 80,000 | 18,000 | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ 8,600,000 |
| Italy | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ 141,000 | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$ 32,346  109,989    138,022    198,200    282,654    7,444  227,499 | | 7,444 | | 25,000 | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ 8,600,000 |
| Spain | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ 141,000 | $\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$ 32,346  109,989    138,022    198,200    282,654    7,444  227,499 | 125,000 | 440,210 | 2,000,000 | 110,000 | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,$ 8,600,000 |
| Australia $\scriptstyle {\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}\,$ British America | | | 10,000 | | 128,000 | 9,500 | 20,000 |
| Chili | 18,300 | 297,029 | 238,500 | 297,029 | 4,000,000 | 299,000 | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \ \end{matrix}}\right\}\,$ 10,000,000 |
| Bolivia | 271,300 | 460,191 | 130,000 | 460,191 | 2,080,000 | 136,000 | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \ \end{matrix}}\right\}\,$ 10,000,000 |
| Peru | 401,850 | 1,000,583 | 303,150 | 1,000,583 | 4,800,000 | 299,000 | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \ \end{matrix}}\right\}\,$ 10,000,000 |
| New Granada | 5,000 | 42,929 | 13,000 | 42,929 | 208,000 | 15,000 | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \ \end{matrix}}\right\}\,$ 10,000,000 |
| Brazil | 1,200 | 2,003 | 675 | 2,227 | 11,200 | 1,500 | $\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \ \end{matrix}}\right\}\,$ 10,000,000 |
| Mexico | 1,440,500 | 3,457,020 | 1,650,000 | 5,383,333 | 28,000,000 | 1,700,000 | 19,000,000 |
| United States | | 1,864 | 17,400 | 73,532 | 352,000 | 1,000,000 | 15,500,000 |
| East Indies | | 56,265 | | 56,265 | | | |
| Africa | | 1,056 | | 1,056 | | | |
| Various other countries | | 33,000 | | 33,000 | | | |
| Total | 2,337,300 | £6,515,925 | 2,827,425 | £8,788,416 | $47,443,200 | 4,017,000 | $53,820,000 |
| Approximate value in U. S. coin | $36,250,000 | $31,537,000 | $43,853,000 | $42,536,000 | $47,443,300 | $62,303,000 | $53,820,000 |
​The following estimate of the world's product of silver in 1873 is based upon returns for Germany, Austria, France, Great Britain, Spain, and the United States, and for other countries upon the most recent available accounts: Great Britain and colonies, $1,000,000; Sweden and Norway, $250,000; Russia, $500,000; Autria-Hungarian monarchy, $1,600,000; German empire, $3,000,000; France, $2,000,000; Spain, $2,000,000; Italy (Sardinia), $500,000; Mexico, $20,000,000; Central and South America, $8,000,000; Canada, $900,000; United States, $36,500,000; total, $76,250,000. According Humboldt and Danson, the value of silver produced in Mexico and Peru from 1492 to 1803 was $4,152,650,000. The production in Europe during the same period was about $200,000,000. For the period from 1804 to 1848 Danson gives $1,244,380,794 as the production of Mexico and South America, that of Europe and Asiatic Russia for the same period having been about $325,000,000. For the period from 1848 to 1868, Prof. W. P. Blake, in his “Report on the Production of the Precious Metals,” gives the following estimate of the silver product: United States $73,000,000; Mexico, $380,000,000; South America, $200,000,000; Australia, $20,000; Europe and Asiatic Russia, $160,380,000; total, $813,400,000. From 1868 to 1875 the product of silver may be approximately estimated at $163,000,000 for the United States, $140,000,000 fur Mexico, $56,000,000 for South America, and $63,000,000 for the rest of the world. (None of these estimates include the produce of Japan, China, and central Asia, of which nothing is known.) We have then, as the grand total of the silver product from the discovery of America to the present time, $7,150,000,000.—Mines. The silver produced in Great Britain is extracted from an argentiferous lead, to the amount of 550,000 to 700,000 oz. annually (in 1872, 628,000 oz.). The celebrated Kongsberg mines in Norway, discovered in 1623, have been worked almost continually since. The ore occurs in parallel belts of rock, intercalated in gneiss and crystalline schists, and impregnated with sulphides of iron, copper, zinc, and sometimes lead, cobalt, and silver. Fissure veins traverse these belts occasionally, and are argentiferous at the intersection only. Beautiful specimens of native silver occur. The total product of the Kongsberg mines from 1624 to 1864 was 1,817,510 lbs. troy of silver, of which 1,332,485 lbs. was produced before 1805 and 463,498 lbs. after 1815, the intervening period being one of discouragement. The yield for the 30 years preceding 1865 averaged $350,000 annually. The silver mines of Sweden are at present insignificant, and the total product in 1871 was officially reported at but 975 kilos. The silver mines of the Austro-Hungarian monarchy are principally comprised in Hungary, Transylvania, and Bohemia. The Schemnitz district in Hungary (the seat of a celebrated school of mines, founded in 1760 by Maria Theresa) is traversed by a group of veins in porphyry, associated with syenite, &c. The ores comprise numerous argentiferous minerals, of which silver glance and galena are the chief. The Schemnitz mines were first opened more than 800 years ago, and have been worked to a depth of more than 1,200 ft. Near Schemnitz are the mining districts of Kremnitz and Neusohl. The Joachimsthal mines in Bohemia are very ancient, very deep (nearly or quite 2,000 ft.), and have been very productive, but now yield an insignificant amount of silver. This district belongs to the Erzgebirge, a chain of mountains composed of crystalline rocks, on the border of Saxony, in which kingdom it includes the four mining districts of Altenberg (tin), Freiberg, Marienberg, and Schwarzenberg. The official statistics of Saxony show that the total product of silver in these districts in 1872 was 48,753 lbs., and in 1873 43,354 lbs. The Freiberg district is by far the most important, containing nearly 100 mines, many of which are more than 1,400 ft. deep, producing almost the whole of the above amounts. Previous to the 10th century it was a wilderness. The lead ores were discovered in the tracks made by wagon wheels, and in 1169 the veins were opened. They are very numerous, but comparatively small. In 1873 only 24 mines were producing silver ore, and of these only 6 paid dividends. The Himmelfahrt, which is now the leading mine, in 1873 yielded 11,912 metric tons of silver, copper, and lead ores, valued at about $430,000. In 1874 it produced about 7,100 tons of dressed ores, sold to the furnaces for about $328,000. The total yield of this mine to the end of 1874 had been 527,103 kilos of silver (worth about $23,000,000), besides lead, copper, zinc, sulphur, arsenic, and nickel. The chief other productive mines near Freiberg, with the value of their total product (including lead, &c.), as paid by the smelting works, for 1873, are as follows: Himmelsfürst, $202,500 ; Vereinigt Feld, $114,750; Churprinz, $74,000; Alte Hoffnung, $61,000; Gesegnete Bergmannshoffnung, $60,750; Alte Hoffnung Gottes, $52,750; Junge hohe Birke, $45,450; and Beschert Glück, $34,600. The principal silver mines of Prussia are in the Hartz, formerly belonging to Hanover. The product of Prussian smelting works in 1872 was 162,553 lbs. of silver, worth about $3,600,000; in 1873, 231,920 lbs., worth about $5,000,000. The total product of silver from the smelting works of all Germany was as follows in the years named:
Value in round numbers. :
| 1850 | 101,448 | $2,284,000 |
| 1860 | 124,103 | 2,764,000 |
| 1870 | 185,847 | 4,162,000 |
A considerable portion of this increase is due to the importation of rich silver ores from ​North and South America for metallurgical treatment, and another portion to the improved processes of extraction. The product from German ores is probably not more than $3,000,000. France is not a silver-ore producing country; but the separation of silver from argentiferous lead ores is carried on to a considerable extent. In 1865 it produced 31,997 kilos of silver, worth $1,414,000; in 1869 (the year before the war), 46,299 kilos, worth $2,020,000. No Spanish silver mines were specially important after the middle ages down to 1825, except those of Guadalcanal and Cazalla, N. E. of Seville, which were profitably worked by the government in the 16th century, producing altogether 400,223 marks of silver; afterward they passed into private hands, and in the beginning of the 17th century are said to have produced 170 marks daily, They were finally abandoned, and allowed to fill with water. In 1825 mining was revived in Spain; in 1839 the famous silver mines of the Sierra Almagrera (N. and S. veins in slate, carrying argentiferous galena, with some silver chloride), in the province of Almeria, were discovered, and in 1843 those of Hiendelaencina (narrow E. and W. veins of silver sulphide and chloride, without lead), in the province of Guadalajara. The Herminia mine, in the Sierra Almagrera, in 1874 produced 18,940 quintals of ore, containing 342,325 lbs. of lead and 41,670 Spanish oz. (3,205 lbs. roy) of silver. The product of the mine in the early part of 1875 was at the rate of about 10,000 lbs. troy per annum. The average value of the work lead is about 20 oz. troy per ton avoirdupois. The product of the mines of Hiendelaencina from January, 1847, to July, 1866, was 7,578,536 oz. troy. They have declined in yield since 1858. By the application of the Pattinson process to the argentiferous galenas of the numerous lead mines of Spain, the production of silver has been increased, The export of lead in 1874 was 86,802,271 kilos, valued at 47,034,022 pesetas. This indicates a value of about $1,700,000 for the silver in the lead. The product of Russia in 1871, from 21 mines of argentiferous galena, was 1,740 tons of lead and 29,000 lbs. of silver.—The conquest of Mexico by Cortes in 1519-'21 was soon followed by the development of the wonderfully rich silver mines of that country. The metal was known to the ancient Aztecs, and was worked by them into numerous ornamental and useful articles; but among the treasures of Montezuma the quantity of silver was small compared with that of gold, and gave little promise of the unbounded resources of the argentiferous mines of his territories. During the 16th century these were opened and extensively worked by the Spaniards in Guanajuato, Zacatecas, and other neighboring districts; and in the 17th and 18th centuries their production was greatly increased by reason of the greater abundance of quicksilver and its more general employment in separating the metal from its ores. At the time of the visit of Humboldt operations were carried on in from 4,000 to 5,000 localities, which might all be included in about 3,000 distinct mines. These were scattered along the range of the Cordilleras in eight groups, the principal of which, known as the central group, contained the famous mining districts of Guanajuato, Catorce, Zacatecas, and Sombrerete, and furnished more than half of all the silver produced in Mexico. The mines of Guanajuato, opened in 1558, are all upon the great vein, known as the veta madre, in the range of porphyritic hills the summits of which are from 9,000 to 9,500 ft. above the sea, but only about 3,000 ft. above the high plateau of central Mexico upon which they stand. The great vein is contained chiefly in clay slate, and crosses the southern slope of the hills in a N. W. and S. E. direction, dipping with the slates (the range of which it follows) from 45° to 48° toward the S. W. It is of extraordinary thickness, often more than 150 ft. across, and is said to have been traced for about 12 m.; but the productive portions are chiefly upon a length of about 1¼ m. The vein is made up of quartz, carbonate of lime, fragments of clay slate, together with large quantities of iron pyrites, and sulphurets of lead and zinc with some native silver, sulphuret of silver, and red silver. Near the surface they are partially decomposed and colored red, whence they are termed colorados. In their unchanged condition below they are designated negros or black ores. These are the main dependence of the mines. The vein has been penetrated to the depth of about 2,000 ft., but not much below the level of the plateau. For the two years ending in July, 1873, 115 mines in this district produced 202,125 kilos of silver ($8,045,425), 36 haciendas and zangerros being employed in reduction. In 1873 the number of miners and laborers was 8,979, and the amount of ore raised was 1,815 tons weekly; average contents of silver, about 34 oz. troy to the ton avoirdupois. The mine of Valenciana, opened in 1760, upon a rich portion of the vein, averaged for many years a product of $1,600,000, or about 1/15 of the total product of the 3,000 mines of Mexico, and a quarter of that of the whole of the veta madre. It declined in productiveness at the beginning of this century, was suspended in 1810 on account of the war of independence, reopened in 1822 by the Anglo-Mexican company, and abandoned after much expenditure to the Mexican owners. It is the deepest mine in the country, and the lower workings are now flooded. In 1873 it employed 1,950 laborers, and yielded about 195 tons of ore weekly. The mines of Zacatecas, opened in 1548, are also upon a single vein called the veta grande, averaging in thickness about 30 ft. The formation is of greenstone and clay slate, the former the most productive. The veins of Catorce are in limestone supposed to be of carboniferous age. The ​greatest proportion of silver in every mining district of Mexico is obtained from the sulphuret of silver, an ore of gray color disseminated through the quartz matrix in minute particles and more or less combined with other metals. The other varieties of argentiferous ores are numerous, but comparatively small in quantity; they are the chloride of silver, ruby silver, native silver, argentiferous pyrites, and argentiferous galena. The comparative quantities of these at the different mines are very variable. Until the present century the ores were extracted altogether by the rude methods of the native Indians. They brought them upon their backs up the long flights of thousands of roughly formed steps, in loads of 240 to 380 lbs. each, while exposed all the time to the great heat of the mine. In 1821 the Mexican government offered facilities for foreigners to become interested with the natives in the mines. English mining companies were formed, and operations were undertaken with powerful machinery; but the adventures were almost universally unsuccessful, the nature of the country being extremely unfavorable for the introduction of heavy machines, as well as for keeping them in operation and repair. From the opening of the Mexican mines in the 16th century their production of silver has exceeded that of all other countries. A great stimulus was given to it by the amalgamating process devised by Medina at that early period in Mexico, and it soon attained an annual rate of from $2,000,000 to $3,000,000. This continued to increase till in the 18th century it rose to $23,000,000, which was about the production for the first ten years of the present century. After 1850 it increased, till for some years it exceeded the yield of all past periods. The total product, from the first working of the mines by the Spaniards to their expulsion by the Mexicans in 1821, was $2,368,952,000. A very promising field for silver mining is found in the state of Sinaloa and along the western slope of the Sierra Madre of Durango and Chihuahua. The port of Mazatlan is the base of supplies. Sinaloa is well wooded and watered; the ores are largely true silver ores, which can be treated by the Freiberg or the modified Washoe process. Some of the mines in the interior are exporting rich silver ores to Europe; others are reported to be earning good profits with stamp mills. Central America has no silver mines that are worked to much extent; but rich ores are known to exist in Honduras, Nicaragua, and Costa Rica.—The famous mines of Potosí in Peru (now in Bolivia) were discovered in 1545 by an Indian hunter, Diego Hualca, who, according to Acosta, accidentally exposed native lumps of the precious metal in the roots of a bush which he pulled from the ground. For 20 years succeeding 1557 the annual production of the mines of this region was about $2,200,000, and the total product up to the present time is rated at over $1,300,000,000. The mines, like so many others in Mexico and South America, are now reported to be flooded in their depths. In the Cerro de Fernando at Hualgayoc, near Micuipamba, rich ores were discovered in 1771, and now, it is said, about 1,400 pits are opened in the hill. Other mining districts in Peru are Gualanca in the province of Huamalies, Pasco, Lucanas, and Huantajaya. Cerro de Pasco has been especially famous for its large production. A town is built upon the site of the mines, and the openings to many of them are through the houses of the miners. The production of Peru until within a few years was very small, probably not more than $2,500,000 annually, and it is a very difficult field for mining. Roads, mules, labor, and fuel are all wanting. The ores (except the pacos or ferruginous earths of Cerro de Pasco), being complex sulphurets, are exceedingly refractory. In the absence of better fuel, llama dung is employed for roasting at several establishments. But the country is full of undeveloped veins, and coal has been discovered in abundance, while railroads are rapidly extending into the interior. In Bolivia, besides the mines of Potosí, are those of Portugalete in the province of Chichas, celebrated for the richness of their ores, which produce six to eight times as much silver to the ton as those of Potosí. Other mines are worked in the same district. The mines of Lipes have been very productive, and those also of La Plata, Porco, Carangas, and Oruro. The earlier silver mines worked in Chili were in the province of Santiago and in the mineral district of Arqueros, about 17 leagues from Coquimbo. The production was not large, and almost ceased upon the opening of the rich mines near Copiapó in the province of Atacama. Within a circuit of 25 leagues from this city there are 19 silver-mining districts, of which those of Chañarcillo and Tres Puntas are the most important. The metal is found in a variety of combinations, as a sulphuret, chloride, chlorobromide, and iodide; it is also associated with arsenic, antimony, and mercury, and is sometimes abundant in a native state. The mines are in a country difficult of access, quite unproductive even in the timber and fuel required for mining, almost entirely destitute of water, and cold and dreary. A new and rich district has been developed at Caracoles, where the ores, like most of those of Copiapó, are chlorides, and easy to reduce.—Silver mining in the western United States, apart from the early operations of the Spaniards in New Mexico and perhaps Arizona, dates from the discovery in 1859, on the E. flank of the Sierra Nevada, in the present state of Nevada, of the now famous Comstock lode. (See Nevada.) No equally important argentiferous deposit has since been discovered; and, in view of the most recent exposures of vast bodies of ore at great depth on the Comstock, it may be doubted whether its ​equal was ever known before. There is no other authentic record of the extraction in a single year of more than $23,000,000 in gold and silver from one vein, which was the product of the Comstock in 1874. And the total estimated product of this lode from 1861 to 1874 inclusive was more than $169,000,000, or about the same as the yield of the score of veins at Potosí for the first 15 years after their discovery in 1545. The bullion from the Comstock lode has averaged about one third gold in value, or say 0.02 in weight. As a consequence of the excitement (almost equal to that attending the discovery of gold in California) which followed the success of the Comstock mines, the districts of Nevada, Idaho, Montana, Arizona, and finally Utah and Colorado, were overrun with prospectors. The mining districts of Owyhee in Idaho, and Unionville, Reese River, Belmont, Pioche, White Pine, and Eureka in Nevada, have been the scenes of successive excitements, and are still productive. In Eureka district, as in the principal districts of Utah, and some of those in Montana, Colorado, New Mexico, and California, argentiferous cerussite and galena are smelted, to produce work lead containing silver. This industry has suddenly grown to large dimensions in the west, as may be seen from the following table of the product of work lead:
Gold, silver, and lead, value. :
| Nevada | 12,812 | $5,043,235 | 11,516 | $3,865,419 |
| Utah | 9,566 | 2,901,191 | 15,474 | 4,332,720 |
| California | 4,000 | 920,000 | 5,095 | 1,680,000 |
| Montana, Colorado, | | | | |
| &c. (estimated) | 300 | 144,000 | 375 | 180,000 |
| Total | 26,678 | $9,008,426 | 32,460 | $10,058,139 |
The Washoe (Comstock) ores and those of Pioche and Owyhee, as well as of many minor districts, are treated by the Washoe process; those of Reese river, Belmont, and Unionville, in Nevada, and of Georgetown, Colorado, receive a preliminary chlorinating roasting. From Colorado and Utah considerable quantities of rich ore are shipped to American and foreign smelting works. Silver mining in Arizona, near the Gila vein, has been rendered unprofitable hitherto by Indian warfare, now apparently ended. The total product of the United States since 1848 is estimated by R. W. Raymond, commissioner of mining statistics, as, follows:
| 1848-1858, inclusive, |
| $50,000 per ann. | $550,000 |
| 1859 | 100,000 |
| 1860 | 150,000 |
| 1861 | 2,000,000 |
| 1862 | 4,500,000 |
| 1863 | 8,500,000 |
| 1864 | 11,000,000 |
| 1865 | 11,250,000 |
| 1866 | 10,000,000 |
| 1867 | $13,500,000 |
| 1868 | 12,000,000 |
| 1869 | 13,000,000 |
| 1870 | 16,000,000 |
| 1871 | 22,000,000 |
| 1872 | 25,750,000 |
| 1873 | 36,500,000 |
| 1874 | 38,200,000 |
| Total | $225,000,000 |
The Atlantic and Mississippi states produce little silver. The amount found with the native copper of Lake Superior is not considerable; but over $2,000,000 has been obtained at the smelting works in Wyandotte, Mich., from the ores of the Silver Islet mine, on the island of that name, on the N. side of Lake Superior. The galena of the Mississippi valley is usually poor in silver, and that of the Atlantic slope is but moderately argentiferous, with an occasional exception, as in the recently discovered deposits near Newburyport, Mass.