SILVER. This beautiful metal has been well known and highly valued from the re motest period—circumstances which are readily explained by the facts of its occurring frequently native, and possessing great lustre and fitness for immediate use without being subjected to any metallurgic process.
Ores of silver.—The ores of silver are ex tremely numerous. Besides the Native silver, the chief ores are the following:—Antintonia/ silver, telluric silver, native amalgam, aurife rous native silver, arsenical antimonial silve-, horn silver, earthy corneons silver, silver glance, earthy silver glance, light red silver, ruby silver, miargyrite, biegsamer silberglanz, flexible sulL phuret, brittle sulphuret, silberkupferglanz, romelite, brittle silver, selensilver, eukairite. selbite, and ganzekothig-erz. Most of these are known by two or three names each ; some occur only in irregular masses, the rest in crystals. The ores which yield silver most readily and most abundantly are native silver, horn silver (chloride), and silver glance (sulphuret). Silver is also procured by cupel lation. [LEAD.] Silver has a purer white colour than any other metal ; it has great brilliancy ; and is susceptible of a high polish. Its specific gravity is about 101. It is sufficiently soft to be cut with a knife ; and is very malleable and ductile, so that it may be beaten into leaves about 1-10,000th of an inch in thickness, and drawn into wire pinch finer than a human hair. It does not rust or oxidise by exposure to the air, but when the air contains sulphu reous vapours it tarnishes, becoming first yellowish and afterwards black. Three metals only, viz. iron, copper, and platinum, exceed silver in tenacity ; a wire of an inch in diameter supports rather more than 187 pounds without breaking. When exposed to a bright red heat silver ,melts'; on fusion its appearance is extremely brilliant, and during this it absorbs oxygen from the air to the amount of about twenty-two times its volume, and this it gives out either by cooling or being poured into water. When leaf-silver, or fine silver wire, is heated by voltaic electricity, it bums with a fine green flame ; if intensely heated in the open fire it boils, and a portion is vapourised.
Oxide of silver gives a yellow colour to glass and porcelain, and is the oxide which is the basis of all the common salts of silver. The chloride of silver is perfectly white, but by exposure to daylight it becomes slowly blueish-white, and eventually almost black.
The direct rays of the sun produce this effect almost instantaneously. On this property is founded its use in photogenic drawing. By mere heat it undergoes no change except fusion, and when it has solidified on cooling it has the appearance of horn ; hence the name of horn silver for the native chloride. It is largely and advantageously used in expe rimental chemistry. The protoxide forms with ammonia a compound called fulminating silver, on account of the facility and violence with which it explodes ; in exploding it forms water, sets free nitrogen, and metallic silver remains. A very gentle heat or alight friction causes it to explode sometimes even before it is dry. Nitrate of silver, when moderately heated, fuses, and being then cast in a mould in small cylindrical sticks, it constitutes the .Argenti Nitras of the Pharmacopoeias, com monly called lunar caustic. When sulphur, phosphorus, or charcoal, is mixed with nitrate of silver, and struck on an anvil, detonation ensues, and metallic silver is obtained. Nitrate of silver is employed by precipitation with carbonate of soda, &c., for writing on linen : it is commonly called Indelible Ink.
Iron and silver combine with difficulty ; they separate on cooling, the iron retaining about one-eightieth of silver, and the silver about one-thirtieth of iron. According to Faraday and Stodart, steel containing about one five-hundredth of silver forms a good alloy for cutting instruments. Iron and silver form a blueish-white granular alloy ; tin and silver a white, hard, brittle alloy. When cobalt and silver are fused together, they separate during cooling, each retaining a por tion of the other. •Lead and silver give a dull brittle alloy ; antimony and silver a white brittle alloy ; arsenic and silver form a gray, brittle granular compound, containing about 14 per cent. of the former metal. Bismpth and silver give a yellowish-white, brittle, lamellar alloy ; molybdenum forms a compact, brittle, gray, granular compound with silver ; and tungsten a brown, slightly malleable button copper and silver readily combine, and the silver is rendered harder by it without much deterioration of colour; the standard silver of this country is composed of 11.10 silver and 0.90 copper. Mercury and silver amalgamate readily, and this compound is sometimes employed for plating, but this operation is now most advantageously carried on by pre cipitation by means of voltaic electricity.