S IL

S I L

( 315 )

Baume are the following: Make an amalgamof one part of leaf filver with feven of mer-cury, which will unite by Ample triture into amafs of the confluence of foft butter. Put afmall lump of this amalgam about the fize of abean, into a bottle containing a mixture of fixdrachms of a faturated nitratof filver with fourdrachms of a fimilar folution of mercury di-luted with five ounces of water. Set the bottlein a place where it may remain perfe£lly atreft, and the expected metallic vegetation willgenerally fucceed. It begins by the appearanceof fmall fpiculse flicking on the furface of thelump of amalgam, which after a while increafeto broad brilliant blades elegantly arborefcent,which, if the bottle is kept at reft, have con-fidence enough to keep together, and imitate afhrub in form.

The time required for this depends on thedegree in which the folution is diluted; in ge-neral, with the above proportions the firft fila-ments form in a few minutes, but it takes aday or two to compleat the precipitation. Thisprecipitate is brittle, harfh to the touch, andvery brilliant. The amalgam on which it isbafed lofes much of its metallic luftre and be-comes much harder than at firft, and brittle,inftead of being of the confiftence of butter.Mercury alone will anfwer the fame purpofe asthe amalgam, but the filver tree is more brittleand fooner falls down by its own weight.

Nitrat of filver is decompofed by the fixedalkalies pure or carbonated, and by the alkalineearths. With the pure alkalies and earths agrey precipitate is formed, with the carbonatedalkalies a yellowifh white. In the former cafe,loo grs. of the precipitate are produced (ac-cording to Bergman and Wenzel) by about 89of filver, and in the latter by about 77.

Ammonia firft gives a precipitate which itfpeedily redifiolves, and forms with fome parti-culars in the management the fulminating fil-ver, which will be prefently defcribed. Car-bonat of ammonia gives a white or a dark pre-cipitate, according as it is more or lefs faturatedwith carbonic acid. All thefe oxyds turnblackifh by expofure to light.

Many other metals alfo feparate filver fromits folutions in this and other acids, and parti-cularly copper, which is employed largely forthis purpofe by the refiners. In allaying gold(as mentioned under the article -djfay) the cu-pelled button of gold and filver is treated bynitric acid to diffolve out the filver and leavethe gold pure. After this procefs (which is

called parting by aqua-fortis ) a nitrat of filvex isleft, which when a fufficient quantity is col-lecled is thrown into a copper bafon fomc-times alfo with pieces of copper immerfed,and the filver is reduced in its perfect metallicftate in the form of thin brittle leaves, and thebafon now contains nitrat of copper. Thelatter again decompofed by lime yields thepigment Verditer. The whole of the filver isnot however feparated by copper, for the folu-tion becomes milky on adding common fait.The reduced filver alfo contains a fmall quan-tity of copper. Still it is a very ufeful andconvenient way of recovering the filver imme-diately in the metallic ftate, and is employedboth in the large way and in analyfis.

Nitrated filver is alfo decompofed by a greatvariety of alkaline and earthy falts, particularlyby the fulphats, muriats, phofphats, &c. thatis by all thofe whole acids united with filverproduce an infoluble fait. Of thefe the muriatof filver is the moft important, and will beprefently mentioned.

Several of the metals are found to combinewith the acids in two proportions, one, wherethe ingredients are in mutual faturation, or elfewhere the acid is in excels, and the otherwhere the metallic oxyd predominates. Prof.Prouft' has given the following account of thenitrat of filver with excefs of oxyd, or fubnitrat.

It is prepared by boiling a faturated folutionof the common nitrat of filver with regulinefilver in that ftate of fine flocculi in which itappears when precipitated by copper. Nitrousgas is given out during the ebullition, which isto be continued for about an hour, and theveil'd then corked and let by that the undiffolvedportion may fubfide.

The folution is of a clear yellow colour,and is the fub-nitrat in queftion. Being muchmore foluble than the nitrat it may be con-centrated to a much greater degree by eva-poration in a retort or mattrafs into which afew pieces of filver are to be put to prefervethe excefs of this metal. During the evapora-tion fome of the fait is volatilized. It is verydifficult to obtain this fub-nitrat in regularcryftals, for, when fufficiently concentrated,the whole is very apt to congeal into a whitefhapelefs mafs, during which a fenfible heat isgiven out.

This folution differs from the common nitratin many particulars. Its colour is yellow, butthe nitrat is without colour; the fub-nitrat

* J. l’hyf. tom. 62, p. 210.

2RJ