TART III,

Metallic Preparations. — Silver.

649

evaporation and melting, a porcelain crucible should be used,as the fused silver is apt to sink into the substance of thecommon crucibles : and it should be of ample size to allow ofthe swelling and ebullition. The heat must not be continuedafter the fusion is complete; for by continuing the applicationof heat, the nitric acid is expelled, and the silver partially re-duced ; but it should be directly run into the moulds, whichmay be made of iron; or, in a mass of well-tempered pipe-clay,holes of the size required may be perforated by means of agreased quill, and the fused nitrate run into them. When cold,each piece must be cleaned from the grease, and separatelyrolled up in clean white paper.

Qualities. — Fused nitrate of silver is in small solid cylindersof a dark grey colour, and presenting, when broken across, acrystallized structure. It is inodorous, has an intensely bitter,metallic, caustic taste, and tinges the skin and hair black where-ever it touches, owing to the reduction of the nitrate by the ex-tension of it on the cuticle. It is not deliquescent; and thepresence of copper in the preparation may always be suspectedwhen this occurs. It is soluble in an equal weight of water at60 °, and is also soluble in alcohol. It is blackened and re-duced by exposure to light or a strong heat, by phosphorus,hydrogen gas, and the hydrosulphurets ; is precipitated fromits aqueous solution by mercury, copper, and some other metals ;and is decomposed by the alkalies, with the exception of amom-nia: by the alkaline earths, sulphuretted hydrogen, the hydro-sulphurets, the sulphuric, muriatic, and arsenious acids, themajority of the neutral salts, and by astringent vegetable solu-tions and hard water. The constituents of 100 parts are, 64of silver, 6 of oxygen, and 30 of nitric acid.

Medical properties and uses. —Nitrate of silver is tonic, anti-spasmodic, and escharotic. It was introduced as an internalremedy by Angelus Sala, in the commencement of the 17thcentury. It is said to prove efficacious in epilepsy, in anginapectoris, and in chorea. In these cases it is given in doses ofone-eighth of a grain, gradually increased to grs. iv. or more,three times a day; but little advantage is gained, unless its usebe preceded by a course of purgatives. The chief objection tothe internal administration of nitrate of silver is the discolor-ation of the skin which it sometimes produces: but M. Semen-tini says this may be averted by the patient avoiding the lightof sunshine. * The best form of administering it is that of pillmade with crumb of bread, or any vegetable extract. Butthe chief use of nitrate of silver is as an external application todestroy strictures of the urethra, warts, fungous excrescences,

1 Giornafc <U Fisica. xi. p. 355.