426
ELEMENTS OF MATERIA MEDICA.
gold, antimony, tellurium, arsenicum, and copper); or combined withsulphur, selenium, iodine, or chlorine ; or united to oxygen and carbonicacid. Of these, native silver and the sulphuret are by far the most abun-dant.
Preparation. —The processes followed for the extraction of silvervary in different places, according to the nature of the ore: they areprincipally amalgation and cupellation. At Freyberg the ore is mixedwith common salt, and roasted, by which the sulphuret of silver is con-verted into the chloride of this metal: water and iron are then added, toremove the chlorine, and the disengaged silver is finally dissolved inmercury ( amalgamation ), and the solution submitted to distillation, bywhich the mercury is volatilized, and the silver left behind (J. H.Vivian, in Taylor’s Records of Mining, p. 21). The process of amalga-mation followed in America is somewhat different (Boussingault , Ann. deChim. li. 337; also Ward, Mexico in 1827, vol. ii. 437).
Silver is obtained from argentiferous galena, as follows:—The ore isfirst roasted to expel the sulphur, and afterwards smelted with charcoal.The argentiferous lead is then submitted to cupellation, by which the leadbecoming oxidized, is partly volatilized, and partly sinks into the cupel( cineritium ), leaving the silver. (On the smelting processes of Hungary ,Saxony , &c., consult Taylor’s Records of Mining, p. 51).
Pure silver is obtained by immersing a copper rod in a solution of thenitrate. The precipitate is to be digested in caustic ammonia, to removeall traces of copper, and afterwards washed with water.
Properties.- —In the native state, silver occurs crystallized in the cubeand regular octahedron. When pure this metal is white, with a slightshade of yellow; inodorous and tasteless. It is moderately hard andelastic; very ductile and malleable: a single grain may be drawn outinto 400 feet of wire, and leaf silver ( argentum in laminas extensum;argentum foliatum ) may be procured, whose thickness is oidy of an
inch. Its sp. gr. is 10’474. It melts at a bright red heat (1873° F.according to Daniell). When exposed to the air it does not oxidate, butreadily tarnishes by sulphureous vapours. Its equivalent is 108.
Characteristics. —It is soluble in nitric acid: the solution thusobtained throws down a white precipitate—[see the properties of thischloride, p.105]—with hydrochloric acid or the chlorides; white alsowith the alkaline carbonates, oxalates, and ferrocyanides; yellow withthe phosphates and arsenites ; red with the arseniates; olive-brown withthe alkalies or lime water; metallic silver with phosphorus or copper;black with hydrosulphuric acid.
Purity. —The silver of the shops usually contains traces of gold andcopper.
Physiological Effects. —Silver in the metallic state is totally inert.
Uses. —In pharmacy it is used for the preparation of the nitrate whichis employed as a medicine and as a test.
Silver leaf is used for filling the hollows of decayed teeth, and wasformerly employed to cover pills. An amalgam of silver is also used bysome dentists for stopping teeth. It is objectionable on account of itsblackening them.