Silver

Silver (AG 107.93). This metal has been known since very early times; it is frequently mentioned in the Mosaic and other scriptural writings, while often in the other works of antiquity notice of it occurs. The sources whence the ancients obtained their supplies are not certainly known; Spain appears then, as now, however, to have been one of the chief seats of its production, while Nubia, Ethiopia, and Greece also possessed silver~mines. Small quantities only occur in Great Britain, though mention of former silver-mines is made by Strabo. The chief localities now noted for the presence of silver-ores are Spain, Hungary, the Hartz, the Urals, Saxony, Mexico, Peru, Colorado, Nevada, while it also occurs largely in numerous other districts. The metal seldom occurs in the free state, but is sometimes met with, crystallising in forms derived from the Cubic system. Its chief ores are the sulphide, or silver-glance, and chloride, or horn-silver. A crystalline compound with mercury is also found in Sweden, Spain, Chili, etc., which possesses a variable composition, and is known as "amalgam." The ores are usually associated with large quantities of other metals, so that they never contain more than a small proportion of the theoretical amount of silver. It occurs to a small extent in most lead-ores, and large quantities of the metal are obtained in lead-smelting, as the lead can be profitably desilverised when the proportion of silver is as low as a few ounces to the ton. [PATTINSON'S PROCESS, PARKES' PROCESS.] For the extraction of silver from its own ores, the methods are well perfected, and can be performed on ores with only .05 per cent. of si1ver. The processes differ, however, with the various ores and local conditions. Silver is, when pure, a bright white metal with a high lustre. It is very ductile and malleable, and is capable of being hammered, into very fine sheets and drawn into very thin wire. It has a specific gravity of 10.5 to 10.6, and is an excellent conductor of both heat and electricity. It melts at a temperature of 1,000° C., and at a higher temperature volatilises with the formation of a purplish blue vapour. It is very stable, and does not rust in moist air; it becomes coated, however, with a film of black sulphide if exposed to the action of sulphur compounds, and to this is due the blackening of silver articles in rooms where gas is burnt. It alloys very readily with other metals; the silver employed in English coinage consists of an alloy of 92.5 silver, with 7.5 of copper, most foreign coins containing a smaller quantity of silver. Silver containing 11 oz. 2 dwt. silver to the pound (Troy) is known as "sterling" silver, and is stamped with the "Hall mark" of a Lion, or if 11 oz. 10 dwt. (95.5 per cent.) of Britannia. If melted in air, silver absorbs oxygen to the extent of twenty-two times its volume, the whole being again liberated when the metal solidifies. It dissolves readily in nitric acid, forming silver nitrate, which crystallises in soluble triclinic tablets and is the most important salt of silver. Fused and cast in sticks, it is known as lunar caustic and employed as a cautery. The chloride, bromide, and iodide are all insoluble in water, and are extensively used in photograpby. The multifarious uses of the metal are too well known to need enumeration. It is usually detected by the precipitation of its insoluble chloride by hydrochloric acid, and may be estimated either in the same way or by the dry method known as cupellation (q.v.).