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without requiring any artificial heat. Towardsthe end however it may be boiled for a fewminutes where perfect faturation is wanted, orwhere every atom of (liver is to be feparatedfrom gold as in the procefs of parting defcribedunder the article AJfay. If the effervefcence istoo violent, fo as to endanger an overflow ofthe contents of the veffel, it muft be moderatedby adding cold diftiiled water.

When the filver contains a little gold as isthe cafe with a large proportion of the ftandardfilver in ufe, the gold is left behind after thefolution of the filver in the form of a blackpowder, which when collected, and fufed witha little borax, appears in its reguline (late.

When the nitric acid contains either muri-atic or fulphuric acid a milkinefs is perceivedas foon as the effervefcence begins, owing tothe feparation of the firft portions of the dif-folved filver from the nitric acid in the form ofan infoluble fulphat or muriat. Where thequantity of thefe foreign acids is but fmall, itdoes not materially impede the procefs, andthefe infoluble falts, after the nitric acid isfully faturated, fall to the bottom by (landingat reft for forne hours.

A lmall quantity of the nitrat of filver isvolatilized along with the nitrous gas duringthe folution, efpecialiy if carried on with rapi-dity, and at a confiderable heat. p This isproved by condenfing the vapour in a receiver,containing a clear folution of common fait,which is thereby rendered milky.

Liquid nitrat of filver is perfectly clear andcolourlefs in cafe the filver was pure, but ifftandard filver be employed the colour is alight blue, owing to the prefence of copper.When at all concentrated its tafte is exceilivelyftyptic and bitter, and it rapidly corrodes the(kin of the tongue. Even in extreme dilutionthe bitter ftyptic metallic tafte, is very fenfi-ble, and it remains for a long time in the pa-late. This fait blackens every part of the (kinand all other animal matters. The blacknefshowever does not come on till after the parthas been expofed for fome time to the light,and is therefore particularly haftened by fun-(hine ; but the mutual adlion between the faitand the skin, is fo fudden, when the folution isconcentrated, that a few feconds of contactwill be fufficient infallibly to produce the ef-fect though it be carefully wafhed off imme-diately after. phis l a {j; s for fieveral days,and only goes off by the natural change of the

f ProuftJ. Phyf

cuticle, fo that in dead animal matter it is in-delible.

The blacknefs is owing to a reduction ofthe metal in excefhvely minute particles; forwhen examined in a ftrong fun-fliine with apowerful microfcope the particles of metallicfilver may be diftinguilhed.

Mod vegetable fubftances are alfo (lamed bythis fait, though in a lefs degree, and lefs per-manently.

When this folution is fufficiently concen-trated it readily cryftallizes on cooling. Theform of thefe cryftals is generally fix-fided, orfquare thin plates, often ranged like the (licksof a fan, and forming very beautiful groups.This fait is not deliquefcent, and is foluble inabout four parts of cold water and much lefsof boiling.

It appears to contain but little water of crys-tallization, for when moderately heated itmelts, and may be kept at that (late withoutlofing more than one per cent, of its weight.By cooling it then concretes into a dark greymafs, which is the nitrat fcarcely altered, andwhen rediffolved in water will again cryftal-lize. This grey folid nitrat forms a very valu-able cauftic for the ufe of furgeons, and forconvenience is caft in oiled moulds into piecesabout the fize of pencils, which are called lunarcauftic or lapis infernalis. This is actually pre-pared however without the trouble of cryftal-lization, (imply by evaporating the nitrat offilver to the proper degree, and cooling therefidue in the proper moulds. When one ofthefe pencils is broken acrofs it prefents a radi-ated texture. The degree of caufticity of thisfubftance is by no means fo powerful as thatof the folid alkalies, for it corrodes the cuticlewith difficulty, and it requires fome hours todeflroy the furface of the flefh.

There are two great agents which modpowerfully decompofe nitrat of filver, lightand heat. Light has no atftion on the liquidfolution when kept in a bottle, full and well(lopped, but if any portion is fpilt, and themoifture evaporates, the remaining nitratblackens, is decompofed, and when diffufed inwater it is no longer entirely foluble, but ablack powder fubfides, which is filver nearly ifnot wholly in the reguline (late, and minutelydivided.

Heat alfo totally decompofes this fait, for ifit is heated at all beyond the (late of lunarcauftic, globules of reduced filver are found

tom. 62, p. 212, &c.

VOL. U.

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