SILVER (syrali. Ag, equiv. 108, sp. gr. 10.Z3) is a metal which. in its compact state, is of a brilliant white color, possesses the metallic luster to a remarkable degree, is capa ble of being highly polished, and evolves is clear ringing sound when struck. It is harder than gold, lint softer than copper, and is one of the most ductile of the metals. It is malleable, may be hammered into very thin leaves, and may be drawn out into very fine wire, the thinnest silver-leaf having a thickness of only proletra of an inch. and one grain of the metal being capable of yielding 400 feet of wire. It possesses a high degree of tenacity, a wire with a diameter of of an inch being able to support a weight of nearly 188 pounds. It requires a heat of 1873° Fehr. to fuse it, and on cool ing expands at the moment of solidification. It is an excellent conductor of heat and electricity, and is not affected by exposure, even to a moist atmosphere at any tempera ture. When, however, it is fused it absorbs a considerable quantity of oxygen which it expels in the act of solidification with a peculiar sound technically known as spitting.* But although it does not rust or become oxidized it usually becomes tarnished on pro longed exposure to the air, owing to the formation of a film of sulphide (or sulphuret) of silver. and this change °emirs more rapidly in towns than in the country in consequence of sulplinreied hydrogen being more abundant in the atmosphere of the former than of the latter. This metal is Unaffected by the hydrates or nitrates of the alkalies, even at a high temperature, and hence silver crucibles, etc., are highly useful in many laboratory operations.
Hydrochloric and dilute sulphuric acid have scarcely any action on silver, but nitric acid and boiling sulphuric acid oxidize it, and form salts; nitric acid being by far its best solvent. Silver has strong affinities for chlorine, bromine, iodine, and sulphur, and combines with the first three and sulphoreted hydrogen at ordinary temperatures. It Is well known that common salt, especially in the melted state, when left for any time in contact with silver, corrodes that metal, soda being formed from the oxygen of the air, while the liberated chlorine attacks the silver.
Silver is frequently met with in the native state crystallized in cubes or octahedrons, or occurring in fibrous masses. It is also found in combination with geld, mercury, lead, antimony. arsenic, sulphur. etc., and sulphide of lead is almost always accompanied with a greater or less amount of sulphide. of silver; it is, however, never found as an oxide.
Silver forms three compounds with oxygen—viz., a suboxide, Ag,0; an oxide, AgO; and a peroxide, Aga. All these oxides possess the common properties of being reduced by heat to the metallic state, and of being very readily decomposed by theactiou of light. The oxide, AgO, is the only one of these compounds requiring si esial notice.
It is a dark-brown heavy powder, devoid of taste or smell, somewhat soluble is water, to which it communicates a metallic taste and an alkaline reaction. It acts as a powerful base, neutralizing the strongest acids, and forming normal salts with them. It is obtained by the addition of a solution of potash to a solution of the nitrate or any other soluble salt of silver. falling as a hydrated oxide, which, at a temperature above 140°, becomes anhydrous. if a concentrated solution of ammonia be digested for some hours upon freshly precipitated oxide of silver, fulminate of silver (q.v.), or fulminating silver in the form of a black powder is produced, and the same dangerous compound is formed when an ammoniacal solution of nitrate or chloride of silver is precipitated by potash.
The salts which the oxide of silver•forms with acids are characterized by the readi ness with which they decompose, the mere action of light blackening and partially reducing them. None of these salts occur in nature, The following are the most important of those which have been formed artificially: Nitrate Silver crystallizes in large, colorless, transparent square tablets, which blacken on exposure to light, or in contact with organic matters, owing to reduc tion, and dissolve in their own weight of cold water. This property of producing a per manent black color with organic matters has led to itlemploymeut as a marking ink* for linen, etc. The black stains which it forms on the skin, on linen, etc., may be removed by the employment of a strong solution of iodide of potassium, or more readily by a solution of cyanide of potassium. The crystals fuse at a temperature or about 425°, and the molten mass, when cast into cylindrical molds, solidifies, and forms the sticks of lunar caustic which are employed in surgery, medicine, and photography (q.v.). Nitrate of silver is prepared by dissolving pure silver in moderately strong nitric acid, and evaporating till the solution is sufficiently concentrated to crystallize. "The most char acteristic test for the salts of silver is the action of hydrochloric acid, or of a soluble chloride, Is hich produces a white curdy precipitate of chloride of silver, insoluble in nitric acid, but readily soluble in ammonia; it is also soluble in hyposulphite of soda, with which it forms an intensely sweet solution; cyanide of potassium ;rho dissolves it; the chloride of silver speedily assumes a violet tinge when exposed to light."—Miller's Elements of uhemistry, 2d ed., vol. ii. p. 732.