Silver (sym. Ag; equiv. 108; sp. gr. between 10.47 and 10.57). This metal was one of the earliest known, and is of a peculiar and beautiful white colour, by which it can be distinguished from all other metals or alloys, except one or two rare metals, such as lithium and indium, which are seldom seen. Silver is harder than gold, but softer than copper. It takes a very high polish, and for this reason was sometimes used for making small mirrors by the ancient Romans. It ranks next to gold in malleability and ductility, the thinnest silver-leaf produced by hammering being only of an inch thick; and a wire of the metal can be drawn so fine that a length of 130 yards weighs only one grain. It has been usually stated that silver has a clear ringing sound when struck, but accurate observers, like Karsten and Percy, say that, on the contrary, a bar of the metal emits a dull sound on receiving a blow. Silver conducts heat and electricity better than any other metal, for which reason it is adopted as the standard represented by 100. Its melting-point has been variously stated, but appears to be about 1904° F. (1040° C.). Silver does not suffer even from long exposure to the atmosphere, except that it readily tarnishes when sulphuretted hydrogen or animal exhalations containing sulphur are present. Both nitric and sulphuric acid dissolve silver; and aqueous hydrochloric acid, as well as a solution of common salt, converts the surface of the metal into the chloride of silver. The metal is not attacked by caustic alkalies.
Oxides of Silver.—Three compounds of silver with oxygen are known. Argentie Oxide or Protoxide of Silver, , is the best defined of the three. If to an aqueous solution of nitrate of silver lime-water or baryta-water be added, this oxide of silver is precipitated. The same brown precipitate is obtained if pure potash or soda be used as the precipitant. The protoxide of silver when moistened absorbs carbonic acid from the air. It decomposes and loses its oxygen at 572° F. (300° C.), and ignition takes place when it is rubbed in a mortar with sulphide of arsenic or of antimony and other easily oxidisable substances. The other two oxides of silver are the Argentous Oxide or Suboxide, , and the Peroxide, .