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of copper may then be applied to feveral ufes.The fir It way however gives a purer filver.

Sulphuric acid impregnated with nitrous gas(a combination firft noticed by Dr. Prieftley)diffolves filver with effervefcence as foon asheat is applied, the folution becomes of a vio-let colour and much nitrous gas is difengaged.By moderate dilution a white faline powderfalls down which is rediflolved in more water.The undiluted folution faturated, and fet in acool place, readily congeals, but when diluted(lightly it gives foliated cryftals.

The carbonic acid has no action on filver orits oxyd, but a carbonated oxyd infoluble inwater is formed by precipitating the nitrat orany other folution by a carbonated alkali. Thisfubftance is a yellowifh white powder, whichby expofure to light, foon turns blackifli, andin time it contains a fenfible portion of metallicfilver. It is a convenient preparation for mak-ing the falts of filver with thofe acids, which,like the acetous, do not a£t on this metal inthe reguline hate.

Muriatic acid is ufually faid to have no ac-tion on reguline filver either hot or cold. Thisis the fact (generally fpeaking) for the actionin a moderate time is fo fmall that the filverhardly appears corroded, though after a certaintime and particularly with the afliftance of heatthe metal is converted into an infoluble muriatand the remaining acid which is proportionallyweakened retains fcarcely a particle of the mu-riat in folution. w But the oxyd of filver readilyunites with this acid and forms a white curd-like mafs infoluble in water. This combinationhowever is more frequently made by the modeof precipitation, and occurs whenever muriaticacid, or any alkaline or earthy muriat is addedto any fait of filver except the pruffiat. In thiscafe if the folutions are at all concentrated, atthe moment of mixture a white curd-like fub-ftance feparates, and fpeedily finks to the bot-tom, which is the mu-'iat of filver or luna cor-nea. This precipitation is one of the moll fami-liar to chemifts, for being perfectly infoluble inwater it fhews itfelf when the molt minutequantities of muriatic acid and filver are pre-fent, and thus it forms a rnoft ufeful tell foreither iubftance.

When the quantity is extremely fmall in-deed, no afitual precipitate can be colledted,but the folutions which were limpid beforemixture become more or lefs opalefcent after-wards. Thus the pureft natural waters con-tain fome particles of common fait or earthy

w Provft.

muriats, and therefore if a drop of nitrated til-ver be fliaken with a bottle full of water, itbecomes almoft immediately milky cr opalef-cent according to the quantity contained. Thisteft is fo delicate that it will even detefib theminute portion of muriat of foda adhering tothe lkin, for if a phial containing diitiiledwater with a drop or two of nitrat of filver befliaken, with the thumb ufed as a ftopper, ina fliort time it will have difiblved enough offait from the furface of the cuticle to becomellightly opalefcent on Handing.

Muriat of filver does not feparate compleatlyfrom the liquor of the folution in which it isformed, till all the filver is precipitated, lorwhilft any remains in folution, though thecurdy precipitate is copious, the fupernatautliquor alfo remains very miiky, but as foon asfufficient muriatic acid is added to engage thewhole of the filver, the liquor becomes limpidalmoft fuddenly. The muriat may then becollected and edulcorated with the utmoft eafe,more fo than any other known precipitate. Itretains the laft portions of water however, withconfiderable obfiinacy, fo that it cannot bethoroughly dried at the heat of boiling water,without remaining in that temperature for aconfiderable time. When perfectly dry it is inhard harfh-feeling lumps, which do not in theleaft foil the fingers.

Muriat of filver melts at a heat fomewhatbelow rednefs, (that is about the degree atwhich lead melts) and flows into a thin yel-lowifh liquid. A fmall portion of it volatilizesduring the fufion, but after it is melted it niaybe kept in a common crucible at a faint red-heat for an indefinite time without fubliming,or finking through the pores of the veflel..Neither does it attack glafs in any degree, butat this temperature is tranfparent and has apearl-grey luftre which is very diftinguifhable.When cold it concretes into a yellowish, toughmafs, tranfparent in thin laminae, flexible,which may be eafily cut with feiffars, and agood deal refembles horn in its appearance,,whence the term horn, filver, or luna cornea,which properly only belongs, to it in this ftatc,but is indiferiminately ufed for the muriat inany ftate, and which we fhall here retain.Luna cornea when cooled in mafs may beturned on the lathe, and fnuff boxes have beenmade of it by the curious. When cooledflowly it has a ftrong tendency to the odohedralform . 31 A ftrong red heat volatilizes it totallyin very denfe white fumes.

* Ibid.