Page:The New International Encyclopædia 1st ed. v. 18.djvu/219

SILVER. 175 SILVER. tallization, when large colorless transpai'ent tablets are formed which blacken on exposure to light or in contact with organic matter. They may be fused and east into sticks or pencils, which form the silver nitrate used as a caustic in medicine. Silver nitrate is the basis of many of the indelible inks, is a constituent of black hair dyes, and is largely used in photography. The haloid salts of silver include the chloride, the iodide, and the bromide, all of which are found native, and may be prepared by the action of a soluble chloride, broiiiidc, or iodide on silver nitrate. These salts, owing to their sensitiveness to light, ai'e extensively used in photography. Silver sulphide, which is formed when hydrogen sulphide is added to a solution of a silver salt, is the black tarnish which forms on silver ar- ticles, and in order to produce the so-called oxi- dized surface on art objects of silver they are immersed in a solution of potassium sulphide. Silver Ores. The following table gives the composition of the principal silver ores, grouped in the order of their importance; The Important Ores of Silver NAME Combining element Formula Xative Silver. Ag. Frequently alloyed with other metals. Argentite. Sulphur. Ag,S As=87.1% Prohstite. (Light ruby silver.) Arsenic and Sulphur. Agj As S3 Ag=GD.4% PYEARGyniTE. (Dark ruby silver.) Antimony and Sulphur. Ag, Sb S, Ag=59.9% Stepbanite. (Brittle silver.) Antimony and Sulphur. Ag. Sb S, Ag=68.D% Cerargteite. (Horu silver.) Chlorine AgCl Ag=75.3% HE381TE. (Petzite.) Tellurium. Agj Te to (Ag Au), Te Tetrahedrite. (Fahl ore.) A complex mix- ture of anti- mony or arsenic sulphides with sulphides of sil- ver and base metal. Very complex. OccuBBENCE. The larger number of the silver minerals given in the above table occur together in many deposits, so that the ores received at the smelting, leaching, or milling works usually consist of a mixture of several silver minerals. Generally native silver and the halogen com- pounds (chlorides, bromides, or iodides) occur in the upper portions of the deposits, while the sulphides, arsenides, and antimonides are found in the lower portions. Tetrahedrite in most cases occurs by itself. The minerals containing silver as an accidental ingredient are galenite (galena), sphalerite, ehaleopyrite, pyrrhotite, pyrite, bournonite, chalcocite, bornite, native arsenic, arsenopyrite, and certain nickel, cobalt, and bismuth ores. Galena often contains silver up to 1 per cent, in quantity (291 ounces to the ton), so that at times the value of the silver in the ore is greater than that of the lead. In Europe the greater portion of the silver output 1.9 derived from galena ores, and in the United States at least 85 per cent, of the annual pro- duction of lead is obtained from argentiferous lead ores, which necessitate the separation of the silver from the lead bullion formed, not only to extract the value of the silver, liut also to render the lead of proper jnirity for commercial purposes. Copper ores frequently contain a considerable percentage of silver, notably in the Butte district, Montana, where every pound of copper extracted contains on the average an ounce of silver. The famous copper schist of Mansfeld, Germany, also carries silver. Silver ores occur in the rocks of various geo- logic ages: in gneiss and allied rocks, in por- phyry, trap, sandstone, limestone, and shales. The veins often intersect eruptive rocks, as trachyte or porphyry, or the sedimentarv' forma- tions in the vicinity of such rocks, and have owed their existence in many cases to the dynamic processes and vapors from lielow at- tending the eruptions. As mentioned above, sil- ver ores are often associated with those of lead, zinc, copper, cobalt, and antimony, and the usual gangue is caleite or quartz with, frequently, dolo- mite or barite. Production. Until recent years the silver mines of Mexico were by far the richest on record, and in spite of imperfect . methods of mining and transportation, Mexico has produced more than one-third of the total output of silver in the world, one-half of the production of the Republic having been derived from the central mining districts of Guanajuato, Zaca- tecas, and San Luis Potosf. According to Hum- boldt, the Veta JIadre lode of Guanajuato alone produced $250,000,000 in silver between 1550 and 1803. The total recorded production of silver in Mexico from 1521 to 1892 amounted to 83,170,307 kilograms, equal in coinage value (.$41.57 per kilogram) to $3,457,389,662, al- though in recent years, owing to the exhaustion of the upper levels in the mines, the production has decreased in value to about $30,000,000 per annum. Until 1860, Bolivia and Peru, followed by Chile, were next to Mexico in the importance of silver production. The total output of silver in Bolivia from 1545 to 1891, was 42.071,231 kg., while that of Peru from 1533 to 1891 inclusive, aggregated 32,199,263 kg., and that of Chile from 1545 to 1891 inclusive, is reported at 4,855,571 kg. In the last few decades the remarkable development of silver-mining in the western part of the United States has increased the out- put so that it now equals that of Mexico, and at present these two countries supply nearly three- quarters of the world's total annual production of this metal. In Europe Spain has been the most productive counti-y. The richest mines are in the Province of Guadalajara. They were ex- tensively operated as late as 1846, but recently the quantity of silver annually produced has de- creased to about 180,000 kg. Austria-Hungary, Saxony, and the Harz Mountain district in Ger- m.any have contributed largely to the total output of Europe. The total production of silver in Germany from 1493 to 1875 inclusive is re- ported at 7,904,910 kg. The silver mines at Kongsberg, >forway, have long been famous, although at the present time the output is comparatively insignificant. Tlie mines of Lau- rion, in Attica, famous in antiquity for their