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Metallic Preparations. — Silver, part hi.

and crystallizations, as long as tabular crystals are pi"oduced,the nitrate of copper being kit in the mother-water. The acidemployed must also be pure; for, if muriatic or sulphuric acidsbe present, the solution is rendered turbid by the formation ofa precipitate of sulphate and muriate of silver; which however,when only in small quantity, does not impede the process, andis easily separated by simple subsidence, after the nitric acid isfully saturated. For the same reasons the water must be pure;and therefore distilled water, or filtered rain water, should beemployed. The granular form of the silver is preferable to thelaminated form ordered by the Colleges. For the subsequentevaporation and melting, a porcelain crucible should be used,as the fused silver is apt to sink into the substance of the com-mon crucibles: and it should be of ample size to allow of theswelling and ebullition. The heat must not be continued afterthe fusion is complete; for by continuing the application ofheat, 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.

Qualifies. —Fused nitrate of silver is in small solid cylindersof a dark gray 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. It is solublein an equal weight of water at 60°, and is also soluble in alco-hol. It is blackened and reduced by exposure to light or astrong heat, by phosphorus, hydrogen gas, and the hydrosul-phurets; is precipitated from its aqueous solution by mercury,copper, and some other metals; and is decomposed by the al-kalies, with the exception of ammonia, the alkaline earths, sul-phuretted hydrogen, the hydro-sulphurets, the sulphuric, mu-riatic, and arsenious acids, the majority of the neutral salts, andby astringent vegetable solutions. The constituents of 100parts are, 64 of 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, and its utilityin angina pectoris, and chorea, is well known. In these casesit is given in doses ofithof a grain, gradually increased togrs. iv.