SILVER (AS. seolfor, scolubr, Goth. si/abr, 011G. silabar, silbar, Ger. Silber, silver; probably from the l'ontie city of 'AXogn, Alybr., where silver abounded). A metallic element that was known to the ancients, and when first mentioned is re ferred to as a medium of exchange. It is de scribed in early Ilebrew writings under the name Kkeph, the root. of which signifies to be pale,' while among the Greeks it was known as dp"opos, argyros, signifying 'shining.' The alchemists called it /um/ or Diana, and referred to it in their writings by the crescent symbol. It occurs native, and specimens weighing several hundred pounds have been found, although it usually occurs in combination, as given below in the table of ores. It also occurs in lead ores, which form one of the main sources of its production. It is found in sea water. and small quantities of it, in the form of chloride, have been detected in volcanic dust. The metal may be readily pre pared by heating silver sulphide with litharge or lead sulphate, the lead being separated from the resulting alloy by cupellation. Metallic silver may also be obtained by reducing silver chloride with zinc, or by fusion with carbon and sodium carbonate.
Silver (symbol Ag.; atomic weight, 107.92) is a white lustrous metal that is very ductile and malleable, with a specific gravity of 10.57 and a melting-point of 1040° C. (about 1900° F.). When in the liquid state it possesses the power of absorbing oxygen from the air, which it gives up on solidification. When a mass of the metal is rapidly cooled, the silver solidifieS before the oxygen has escaped from the interior, and this gas then bursts through the crusts, driving out part of the fused silver in globular masses and exereseenees—a phenomenon known as 'spitting.' Metallic silver finds extensive use in coinage, and, owing to the high polish it takes, for table ware and decorative articles; for silver plating. the silvering of mirrors, and to a slight extent for laboratory purposes. Silver forms alloys
(q.v.) with many metals, and that consisting of 9 parts of silver to 1 part of copper is the standard alloy used for the United States coins, while 835 parts silver to 165 parts copper is the standard employed in the Latin Union. An alloy of 100 parts of aluminum with 5 parts of silver is for making pans of balances, etc., as it is harder and more easily polished than alumi num.
With oxygen silver forms three oxides, an ar gentous oxide or sub-oxide, a protoxide or normal oxide, and a peroxide or dioxide. Of these the protoxide is the most important. It is obtained as a brown pnl•erolent precipitate when silver nitrate is treated with potassium or sodium hy droxide. This compound is used to give a yellow color to glass, and finds some employment. in medicine as a substitute for silver nitrate. Silrer nitrate, or 'lunar caustic,' is prepared by dissolv ing silver in nitric acid and evaporating to crys tallizatiou, when large colorless transparent tablets arc formed which blacken on exposure to light or in contact with organic matter. They may be fused and cast 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 ha loid salts of silver include the chloride, the iodide, and the bra/nide, all of which are found native, and may be prepared by the action of a soluble chloride, bromide, or iodide ou silver nitrate. These salts, owing to their sensitiveness to light, are 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.