SILVER, a precious metal. It appears to have been known almost as early as gold, and, without doubt, for the same reason, because it occurs very frequently in a state of purity in the earth and requires but an ordinary heat for its fu sion. Pure silver is of a fine white color. It is softer than copper but harder than gold. When melted its sp. gr. is 10.47; when hammered, 10.510. Its chemical symbol is Ag. It is next in malleability to gold, having been beaten into leaves only .00001 of an inch in thickness. It may be drawn out into a wire much finer than a human hair, and a wire of silver 0.078 of an inch in diameter is capable of supporting a weight of 187.13 pounds avoirdupois. It excels all other metals as a conductor of heat and electricity. Silver melts when heated completely red hot, and may be boiled and volatilized by a very strong and long-continued heat. When cooled slowly crystals of silver may be obtained. Silver is not oxidized by exposure to the air, or affected by water, but it is blackened or tarnished by sul phuretted hydrogen. The at. wt. of silver is 107.9. Oxide of silver (Ag2O) is pro duced by dissolving silver in a solution of nitric acid and precipitating with an alkali. Its sp. gr. is 7.14. The compound called horn silver or chloride of silver (AgC1) is obtained by dissolving silver in nitric acid and mixing the solution with a solution of common salt. Its sp. gr. is 5.550. When exposed to the light it turns to a blackish color, hence its great use in photography. Bromide of silver is the most sensitive to light of any known solid. It is used for coating the "dry plates" employed in photography. When silver is long exposed to the air it acquires a covering of a violet color, which deprives it of its luster; this coat ing is sulphide of silver. Sulphide of silver occurs native as silver glance. Sil ver readily forms alloys with iron, steel, lead, tin, and mercury. Of the combina tions of acid and silver the most impor tant is nitrate of silver (AgNO3), obtained by dissolving silver in nitric acid. If the silver and acid are pure the solution of silver nitrate is colorless, very heavy, and caustic; it stains the skin and all animal substances an indelible black; after evaporation it deposits, on cooling, transparent crystals of NITRATE OF SIL VER (q. v.).
There are five important silver ores, native silver, vitreous silver (or silver glance), black silver, red silver, and horn silver. The first is usually found in den tiform, filiform, and capillary shapes, also in plates formed in fissures and in superficial coatings; luster metallic; color silver-white, more or less subject to tar nish; ductile; hardness between gypsum and calcareous spar; sp. gr. 10.47. Na tive silver occurs principally in veins, traversing gneiss, clay-slate, and other pakeozoic rocks, but not usually in great quantity. It often forms a natural alloy with gold. Vitreous silver presents itself in various shapes, and is of a blackish lead-gray color with a metallic luster. It
is malleable, about as hard as gypsum, and subject to tarnish; sp. gr., 7.19. It is more or lesspure silver sulphide, and has been found almost exclusively in veins along with ores of lead, antimony, and zinc. It occurs in Saxony, Bohemia, Hungary, Mexico, and Peru; and is an important species for the extraction of silver. Black silver generally occurs in granular masses of an iron-black color.
It is sectile and about as hard as gyp sum; sp. gr., 6.2. This mineral is a com position of silver (about 68.5 per cent.) with antimony and sulphur and traces of iron, copper, and arsenic. It is found in veins along with other ores of silver, and is a valuable ore for the extraction of silver. It occurs chiefly in Saxony, Bo hemia, Hungary, and the American con tinent. Red silver is found in crystals and often massive, granular, and even as an impalpable powder. It is a double sulphide of silver and antimony, contain ing on an average 60 per cent. of silver. It occurs in veins with other silver ores, galena, and blende. It is found in various parts of Saxony, also in Bohemia, Hun gary, and Norway; but chiefly in Mexico, Peru, and the western United States. Horn silver, or silver chloride, occurs in crystals and also in crusts and granular masses. It contains about 76 per cent. of silver. It is found in the upper parts of veins in clay-slate, and also in beds with other silver ores or with iron ochre. It is not abundant in Europe, but occurs in large masses in Mexico and Peru.
Silver is extracted from its various ores by smelting or amalgamation.
The silver mines of North and South America are incomparably more impor tant than those of all the rest of the world. The Mexican mines were worked before the Spanish conquest, and produced large quantities of silver. There are great deposits of silver in Nevada, Ari zona, California, Colorado, Idaho, Mon tana, New Mexico, and Utah. Silver ore, chiefly argentiferous galena, has also been found in great quantities in the Barrier Ranges of New South Wales.
In the Andes Mountains and adjacent sections are marvelous deposits of silver and other minerals, especially iron and copper. Bolivia is unsurpassed in her possession of extensive and rich silver mines. Peru is but little less fortunate in her silver resources and it is said more than 2,000 yielding mines are within her boundaries. At Hualgayoc, in northern Peru, and at the base of the W. spur of the Andes, there are within 40 square leagues 400 silver mines, some of them yielding 300 ounces to the ton. Indians are employed to work in these mines and their only tools are drills, hammers, and raw-hide sacks. They fairly burrow through the mountain, gathering only the richest parts of the ore.
Considerable quantities of silver are produced in Europe. The average pro duction of Germany (before the World War) was about $8,000,000. In Great Britain silver is obtained from argen tiferous lead ore.
The following is the production of sil ver in the United States in 1919: