S IL

SIL

( 299 )

by methods which have been already defcribedwhen treating of that metal and of the art ofassayinc. Two or more affays of the fame oremuft be undertaken, and no dependence oughtto be placed on the refult except they verynearly correfpond.

The analyfis of an ore differs from its affay inthis, namely, that its objeft is to afcertain notone alone, but the whole of its ingredients, andtherefore mull be undertaken in the moift way.For the molt numerous and beft analyses of thevarious ores of filver we are indebted to Klap-roth , and as mod of thefe are models of chemical{kill and dexterity, we {hall relate the particularsof them, with fuch remarks as the fubjeft mayrequire.

i. Hornftlver. c Two hundred grains of a maf-five variety of this mineral were treated withthrice their weight of pure nitric acid, but noperceptible action took place, either in the coldor at a boiling heat, except that a little ironochre was feparated. The folution being de-canted and mixed with ammonia, an additionalportion of oxyd of iron was thrown down ; thefupernatant liquor became opalefcent on mixturewith muriatic acid, but no precipitate was depo-rted ; hence it was manifeft that the muriatedfdver in the ore was not mixed with any in themetallic or fulphurated ftate, otherwife it wouldhave been taken up by the nitric acid and haveafforded a precipitate with the muriatic acid.The infoluble part of the ore was then treatedwith twice its weight of fait of tartar, andyielded 133 grains of reguline filver. On thispreliminary information the following analyfiswas founded.

a. Two hundred grains of the ore were mixedwith 600 grains of cauftic potafh, and fufed ina glafs retort. After refrigeration, the neck ofthe retort being broken off, the fufed mas wasfoftened with hot water, and every thing folublein this menftruum being taken up by it, theliquor was obtained clear by filtration.

b. The infoluble portion was then digeftedin nitric acid, by which the greater part of itwas taken up.

c. The part infoluble in nitric acid was di-gefted in aqua regia, and there remained undif-iolved a few grains of a white colour, whichproved to be muriat of filver, with a little of theearthy matrix of the ore. This muriat of filverafforded (probably by fufion with potafh) 2 grs.of pure filver. The nitro-muriatic folution being

daco.mpofed by ammonia, gave 7 grains of oxvdof iron . 0/0

d. To the nitrous folution (b) was added afolution of common fait, and the muriated filverthus obtained afforded by fufion with foda,134) grains of pure filver. The fluid remain-ing after the feparation of the muriated filver,gave by faturation with ammonia 5 grains ofoxyd of iron.

«■ The alkaline aqueous folution (a) beingfaturated with diftilled vinegar, there precipi-tated 3! grains of alumine; which being fepa-rated the liquor was evaporated to drynefs, andthe product then digefted in alcohol, by whichthe acetite of potafh was taken up, leaving themuriated potafh behind 5 which latter by folu-tion in water, evaporation, and cooling, yielded117! grains of muriated potafh.

f. The muriated potafh being again diffolvedin water, there was added muriated barytes, bywhich a precipitate of about 3 grains of fulphatof barytes was obtained. This is confidered byKlaproth as indicative of i | grains of fulphatedpotafh, which reduces the amount of muriatedpotafh to 116 grains, in which the muriatic acidamounts to 42 grains.

From thefe refults the contents of the ore areftated at per cent.

67.75 Silver21. Muriatic acid

6. Oxyd of iron

1.75 Alumine0.25 Sulphuric acid

96-7 5

The mode of analyfis here adopted appears t»be perfectly fatisfadfory, but there feem to bea few overfights in ftating the refults.

1. The filver is a little under-rated, its amount,according to proceffes c. and d. being 136.5 or68.25 per cent.

1. There is no notice of the oxygen, whichforms an effential part of muriated filver, and inconfequence of this omiffion, the muriatic acidis probably eftimated much too high. Theamount of the filver may be confidered as afcer-tained with the moft exachiefs as it was actuallyreduced to the reguline ftate. Affuming thistherefore as the bafis of our calculations, andthat 100 parts of muriated filver confift of 75.24filver, 8.16 oxygen, and 16.6 acid, it followsthat 136.5 of filver require, in order to be con-verted into muriat of filver, 14.72 of oxygenand 30.04 of acid. But 30.04 of muriatic acid,when faturated with potafh, would afford onlyabout 84 of muriated potafh, inftead of 116, as

* Klap. Aaaalyt. Eff. I. p. Il6,

2 P 2