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Muri.it of filver when newly precipitated isof a delicate white colour, but this changes veryfpeedily and in a very ftriking manner to a greyllate colour by a fhort expofure to light, whichis an ufcful mark of diftincftion between this andmany other metallic precipitates. The changehowever is quite fuperficial. In a ftrong fun-fliine it takes place very rapidly, and it wasdiicovered by Scheele that when the rays arefeparated by a priifn and thrown feparately onthe muriat, the blackening took place in twenty-four leconds in the violet ray, and in an in-creafmg diftance of time in the fucceflive coloursof the 1 peel rum, fo that in the red ray, no lefsthan twenty minutes were required. Mr. Ritterof Jena has fince found that as there areinvifible heat-making rays exifting on the outfideof the prifmatic fpectrum beyond the red ray,(difeovered by Dr. Herfchell, and mentionedunder the article Caloric) fo there are invifiblerays on the other fide of the fpeftrum, beyondthe violet ray, which poffefs in the higheftdegree the chemical effedis known to be pro-duced by fenfible light, and particularly that ofblackening muriat of filver. This was alfodifeovered about the fame time by Dr.Wollafton.Mr. Ritter alfo afferts that if the muriat alreadyblackened in the violet fide of the fpeftrum, betransferred to the red fide, the whitenefs ispartially reftored. Thefe very curious experi-ments however belong more properly to thefubjedt of light.
As the muriat of filver is produced in a greatvariety of analytical experiments, and ferves todetermine the quantities, both of muriatic acidand of filver in any compound, it becomes ofgreat importance to determine with perfeftaccuracy the proportion of the conltituent partsof this tilt. Fortunately its compofition is founiform, its iufolubility in water is fo perfect,and the neceflary proeeffes of edulcoration arefo eafy, that there is an almoft abfolute agree-ment in the refults of the experiments of diffe-rent chcmifts, regard being had to the circum-ftances of drying and redu&ion. It has beenfound by Klaproth that ioo parts of pure filverdiffolved in nitric acid, and precipitated bycommon fait, yield about 133 parts of lunacornea, dried at a heat fuperior to that ofboiling water, hut fhort of its melting point,that is to fay, thoroughly dcficcated, but with-out the volatilization of any of its conflituentparts. Other chemifts agree very clofely withthis refult, and from the average of thofe that.appear entitled to the molt confidence, we may
eftimate 100 grs. of luna cornea thoroughlydried but not melted, to contain 75.235 grs. offilver.)' The remaining 24.765 grs. thereforeconfift of muriatic acid and oxygen. Of thelatter, it is eltimated by Prouft that 100 partsof filver take about 9.5 during folution in nitricacid, and the metal probably exifts in the fameflate of oxygenation in the muriat. If this iscorrect, the oxygen in 100 grs. of dry lunawill be about 7.15 hence the component partswill be
Muriatic acid 17.615Silver - - 75.235Oxygen - - 7.15
100.000
It Ihould be obferved however that Kirwanand other chemifts eftimate the quantity ofoxygen taken up by 100 grs. of filver, to be asmuch as 10.8, which would make the oxygenin 100 grs. of luna cornea to be about 8.1, andwould reduce the muriatic acid to about 16.6.The proportion of filver, however, is more cer-tainly afeertained, and the above eftimationmay be fafely taken without danger of anymaterial error.
Muriat of filver Iofes fome weight whenpaffing from the ftate of perfedt deficcation tofufion, but when melted it may be kept infufion without further lofs, the heat not beingraifed much higher than neceflary. Dr.Thomfon found 132.35 grs. of luna corneadried at 400° (the produdf of 100 grs. of filver)to be reduced to 128.67 grs. by fimple fufion,whence 100 grs. of fuled luna cornea maybeeftimated to contain 77.36 grs. of filver inlteadof 75-235 as given above.
Muriat of filver is nearly if not abfolutelyinfoluble in any acid except the muriatic, butthis acid diffolves it without difficulty whenheated, and the muriat may then he obtainedin odlohedral cryftals. If this folution bediluted with water the muriat feparates in itsufual form. 1 Luna cornea is foluble in pureammonia without decompofition, and when thisfolution is evaporated in the temperature of theatmofphere, the muriat is left either in fmallcubes or in glittering feales, the latter of whichrefemble very clolely the fuperficial fcaly in-cruftation of the native luna cornea.* But ifthe folution is evaporated by artificial heat, thefirft particles that fall to the bottom are thefulminating oxyd, and when fhaken in theflighted degree will d^onate with extreme vio-