SILVER (Ag., from the Latin argentum). This metal has been known from the earliest times, frequent mention being made of it in the writings of Moses. Occurring naturally in the metallic state, though not so frequently as to render it common, and being easily worked, it must, no doubt, have been one of the first discovered metals. The alchemists and astrologers supposed it to have some mysterious connection with the moon, gave it the sign 3, and called it Diana or Luna. They also seem to have been acquainted with chloride of silver (born-silver) and nitrate of silver (lunar caustic).
Next to the free metal itself, the sulphide is the most important oro of silver. It is usually associated with sulphide of lead ; indeed galena lead-ore nearly always contains silver, which is separated as described under LEAD, 3IANUFACTCRE OF. The ore is roasted to expel sulphur, smelted with charcoal, and the argentiferous lead submitted to cupellation [Assaviaa], by which the lead, becoming oxidised, is partly volatilised, partly raked off the surface, and partly sinks into the cupel, leaving pure silver in the liquid state.
Another process for the extraction of silver from its ores is termed amalgamation, from the fact that the metal, after the ore has been roasted and the silver reduced by scrap iron, is dissolved out by mer cury; the separated amalgam is afterwards submitted to distillation, when the mercury volatilises and the silver is left behind. [AstsLoast.] The processes, of which the final step is amalgamation, are many; the ores at different places, being associated with various matters, require diEerent modifications of treatment. One metallurgist, Augustin, die penees with the use of mercury altogether. 7lervogel at once obtains sulphate of silver by roasting the ore at a particular temperature, and precipitates the metal therefrom by copper.
Silver is almost pure white, Laving only the faintest tinge of red. In the native state it svmetintea occurs crystallised in cubes or °etc, lustre. It is moderately hard, elastic, and very ductile and malleable ; one grain nos- be drawn into 400 feet of wire, and the thinnest silver foil, or has a thickness of only of an inch. Silver
melts at a bright red heat, and b' repeated fusions becomes quite brittle. It volatilises in the luminous are of a powerful electric current, yielding a beautiful green-coloured vapour. Of all metals, sillsr is, perhaps, the beat conductor of heat and electricity. it does not oxidise at ordinary temperatures, but when molted has the pro perty of absorbing many tunes its bulk of oxygen, which, however, is given out spun at the moment of solidification. Though silver does not runt in the air, it rapidly tarnishes, owing to the formation of n thin him of sulphide of silver this occurs more quickly in urban than in rural districts, sulphur in the form of aulphurettod hydrogen being far more abundant in the atmosphere of the former than iu that of the latter localities.
Silver Is not readily acted upon by alkalies, hence it is of peculiar value in the manufacture of vessels in which :elkaline fusions have to bo made. Common salt, especially in the melted state, is slowly decomposed by silver, soda being formed, from absorption of oxygen, while liberated chlorine attacks the metal Boiling sulphuric acid oxi dises silver ; hydrochloric acid acts but slightly upon it ; aqua regis attacks it readily ; but its best solvent is nitric acid.
Perfectly pure silver may be obtained by dissolving the commercial metal in nitric acid, precipitating with hydrochloric acid, and then fusing the well-washed chloride with half its weight of dried carbonate of soda. In the place of carbonate of soda, carbonate of limo and char coal are sometimes employed. Chloride of silver may also be reduced by placing it iu contact with seine and dilute sulphuric acid.
The equivalent of silver is 108. • Silver and oxygen form three compounds :— 1. Suboxide of silver Citrate of silver is heated to 212° in a current of hydrogen; on dissolving the resulting mass in water, and adding an alkali, the suboxide is precipitated as a black powder. When dry, it acquires metallic lustre under the burnisher.