Of the haloid salts of silver, several occur native. The most important of these compounds is chloride of niter (AgC1), which is found native either in cubes or in a dense semi-transparent mass, and is known as horn silver, and may be procured as a dense white flocculent precipitate by the procedure described in the preceding paragraph. In consequence of its sensibility to light, it is employed in photography. When heated to about 500°, it fuses into a yellow fluid, which, on cooling, solidifies into a yellowish gray semitransparent horny Mass. This salt is insoluble in water and in all the diluted acids, but dissolves in a solution of ammonia, from which it crystallizes in cetaliedra. Its solution in a solution of hyposulphite of soda is employed in silvering iron. copper, and brass goods. Traces of this salt are found in sea-water, the chloride of sodium probably acting as the solvent. Bromide of silver (AgBr) is found in Mexico, where it is known as pla ta vole, or green silver, in the form of small crystals or crystalline granules of a pale olive-green tint. Iodide of sliver (Agl) occurs native in several Mexican mines in the form of thin, flexible, pearly scales.
• Sulphide (or svlphnret) of silver (AgS) is the principal ore of silver, It occurs native, sometimes crystallized in cubes or octahedra, and sometimes in masses. From its gray metallic luster, it has received from mineralogists the name of silver glance. It is well known that if silver spoons arc allowed to remain in contact with boiled eggs for some time, they become tarnished by the action of the sulphur; a minute quantity of sulphur eted hydrogen being probably evolved. The discoloration is easily removed by wash ing the darkened silver with a solution of cyanide of potassium. Sulphide of silver -unites with various other metallic sulphides when fused with them, especially with the sulphides of arsenic and antimony. Red silver ore (3AgS,SbS,) is a native compound of this kind.
The alloys of silver and copper (see ALLOY and Musts), when cast into ingots, arc usually found to differ in their composition in the internal and external parts, in con sequence of a molecular change that takes place during the cooling and slow solidifica tion of the molten mass. In bars containing more than 719 parts of silver in 1000, the central portions are richer in silver than the exterior; in alloys of less value, the reverse is observed, while in ingots containing. 950 or more parts of sil"°r in 1000. the composi tion is nearly uniform throughout. When exactly 719 parts of silver and 281 of copper are conildned (corresponding. to the formula Ag:Cti.), no separation' whatever of the metals occurs. metals, as tin, zinc, antimony, bismuth, arsenic, etc., when mixed with silver, render it brittle and unfit for its ordinary uses; they are, however, easily removed in the process of refining. An alloy consisting of 5 parts of silver, 6 of brass, and 2 of zinc, is used as a solder for silver. An alloy of silver and mercury, known as silver amalgam, occurs native in a crystallized form. It is a mineral of a silvery white color. mid its composition is represented by the formula, Ag Silver, like gold, has been known and prized from the earliest ages. The silver
mines of Mexico were, until quite recently, by far the richest known to exist. Their estimated annual yield is about 1,600,000 lbs. troy of the pure metal. Until the remarka ble discoveries of silver ore in Nevada and adjoining states in 1859 and 1860, Chili and Peru had long stood next to Mexico in their yield, 'each furnishing about one-sixth of the produce of that country. Bolivia is also rich in silver; but the recent extraordinary develop:nent of silver mining in the western regions of the United States, appears to have raised their produce to at least a par with that of Mexico, so that these two min• tries now furnish three-fourths of all the silver obtained in the world.
Of European countries, Spain is the most productive, the richest mines being those of Hiendelaencina, in the province of Guadalaxara, which were first extensively opened in 1816. These have yielded immense wealth, but their produce has much declined since 1853. Silver glance is the principal ore, although several others are found, includ ing quantities of the formerly rare mineral freieslebenitc, which contains about 23 per cent of silver. Next to Spain, Austria, Saxony, and the Harz district in northern Ger many, yield the largest stipples. The silver mines of Konigsberg in Norway are like wise valuable, and have been long famous. Great Britain has no silver mines, properly so called, but since the introduction in 1829 of Pattinsou's process for thedesilverizing of lead smelted from argentiferons galena, a large quantity has been annually produced in this way. The highest yield of silver by this process was in 1868. and amounted to 841,3'1 ounces, but owing to the gradual decline since then in the produce of British teal, the silver obtained from it had fallen in 1875 to 483,432 ounces (see Lm D). In the mineral veins of Cornwall, some "bunches" of true silver ore have occasionally been found, but of limited extent. • The form; in which silver is found in nature are numerous, but we need only notice a few of them. It is frequently foond native in crystalized and amorphous masses, which are sometimes of considerable size. One fine piece found at Koaigsberg is now in the Copenhagen museum, and 5)) lbs. Bat the quantity of silver found in nature in the metallic state is comp tratively smtll. Its principal ores are the different stilphi Ics or sulphurets, viz., silver gl tnee, or sulphuret of silver, containing when pure. 87 pints of silver and 13 of sulph ir; brittle silver ore, or sulphuret of silver an 1 anti many, of which the composition is, silver 61.5, antimony 14.7, and sulphur 16.4; and red silver ore, called also raby silver, of which there is a dark and a light kind, the com position of the former being similar to brittle silver ore, but it is a little le;s rich in silver, and the latter only differs in containing arsenic instead of antimony. The bulk of the silver obtained in Mexico an 1 Sloth Xmerics is got fryn these ores. The only other of much importance, except the mixed ores to he presently noticed. i; horn silver, or chloride of silver. In a pure state, it consists of silver 75, and chlorine 25. It occurs extensively in Mexico and Peru, but is not common in European mines.