part in. Metallic Preparations. — Silver.

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Nitras Aroenti. Edin. Nitrate of Silver.

" Take of pure silver flatted into plates and cut, one part ,-nitric acid diluted, two parts ,■ distilled water, one part. Dis-solve the silver in the acid and water previously mixed to-gether, in a phial with a gentle heat, and evaporate the solu-tion to dryness. Then put the mass into a large crucible,and place it on the fire, which must be at first gentle, and gra-dually increased until the mass flows like oil; then pour it in-to iron pipes previously heated and rubbed with grease.Finally, let the preparation be preserved in a well stoppedglass vessel."

Dublin.

" Take of silver flatted into plates and cut; nitrous acid,each one ounce ; distilled water, two fluid ounces. Put the sil-ver in a glass vessel placed in a sand-bath; and- pour over itthe acid previously diluted. Then dissolve the metal with agradually- raised heat, and evaporate the solution to dryness.Put the mass which remains into a crucible, and dissolve itover a slow fire; finally, let it be poured into proper moulds,and preserve it in a well stopped glass vessel."

In this process the acid is partly decomposed by the silveiwhich is oxidized, and the oxide dissolved as it forms, in theremaining acid. The effervescence is very violent, owing tothe extrication of the nitrous gas of the decomposing acid,which flies off" in orange-coloured fumes, part of them, how-ever, is retained in the solution, and gives it a blue greenishcolour, which goes off as it cools. In this stage of the pro-cess, the silver held in solution is in the state of an oxyni-trate, which, by due evaporation, may be obtained in brilliant,irregular, thin, six-sided plates, having an intensely bitter taste:and although by the subsequent melting a part of the acid iaexpelled, yet it is probable that the product is not reduced tothe state of a subnitrate.

The difference in the quantity of acid ordered in the diffe-rent formulae does not alter the nature of the product; but itis of some consequence, in an ceconomical point of view, toknow, that even in the Dublin formula, which orders equalparts of silver and acid, the quantity of acid is too great, tenfluid drachms being amply sufficient for the solution of twoounces of silver. Several minute particulars are necessary tobe attended to in conducting the process. The silver must beperfectly free from any alloy of copper, which renders the saltalways more or less deliquescent. Its presence is indicatedwhen the solution remains of a permanently greenish blue co-lour : in which case it may be purified by repeated solutions