Z I N

Z 1 N

( 500 )

acid, decompofed by carbonat of foda, and theprecipitate thus procured, after ignition, is oxydof Zinc .

h The refidue infoluble in ammonia (e) is tobe abftrafted repeatedly with nitric acid, andthen digefted in cauftie foda: what remains in-foluble is oxyd of Iran , with a flight contami-nation of arfenic.

i The preceding foda folution is to be fatu-rated with nitric acid, and nitrat of lead is tobe added till it ceafes to produce a precipitate.This precipitate is arfeniat of lead.

k To the remaining fluid is firlt to be addedfuiphat of foda, in order to get rid of any nitratof lead that it would probably contain, and thefiltered liquor being decompofed by carbonatedammonia a precipitate will fall down, which,when well walhed and ignited, is pure alnmine.

A confiderable difficulty however Hill remainsin eftimating properly the relative proportionsof Blende, even after the anal'yfis has been per-formed in the molt careful manner. This arifesfrom the uncertainty of the ftate in which thenine and fulphur (which are the principal in-gredients) exilt in this ore. According to fomechemifts, pure blende, exclufive of all cafualadmixtures, is a true fulphuret of zinc, thelatter being in the metallic ftate. The reaTonsadduced in favour of this opinion are, Firft,that this is conformable to the compofition ofthe other native metallic fulphurets, fuch as thedifferent fpecies of pyrites, and the fulphuretsof lead, antimony, fih/er, &c. Secondly, thatif blende be digefted in muriatic acid fulpbu-retted hydrogen will be given out (as was firftobferved by Bergman) which gas can only pro-ceed from the decompofition of water by themetallic zinc, and the union of its hydrogenwith part of the fulphur, while in the adft ofbeing feparated from the zinc by the powerfulaffinity of the acid for this laft.

On the other hand, however, It may be re-marked that metallic zinc and fulphur cannot bemade to combine together by art, but that oxydof zinc and fulphur unite by fufion, producinga yellowilh compound not unlike blende. Thetranfoarency of this mineral is a Mb a characterin which it differs from the other proper metal-lic fulphurets. It is true that fulphurettedhydrogen is given out during its folution inmuriatic acid, but this would alfo happen if thefulphuretted hydrogen pre-exifted in the ore.It is the opinion of Vauquelin that blende is afulphuretted oxyd, which often contains befidesfulphuretted hydrogen, and this feems to be

confirmed by the obfervation cf Bergman d thatconcentrated lulphuric acid feparates fulphurettecfihydrogen from blende; which cannot happenwith a proper metallic fulphuret. The deductionhowever from this fact is fonrewhat equivocal,for the proportion of fulphuretted hydrogen byconcentrated fulphuric acid is greatly inferiorto that produced by muriatic acid, and when itis confidered that all blende affords by diftilla-tion a portion of water, is it not very poflibfothat the hydrogen may be furnilhed by the de-compofition of this lalt ? But the production offulphuretted hydrogen from- it, by the agencyof acids, by no means proves that the zinc multneceffarily be in one of the forms above-men-tioned; common liver or glafs of antimony,,which is decidedly a fulphuretted fub-oxyd,affords fulphuretted hydrogen when digeftedwith acids, and it appears highly probable, ontaking into confideration all the properties ofblende, that- this alfo is a fulphuretted fub-oxyd;

The ores of zinc cannot be- affayed in dis-common method'on account of the great vola-tility of this metal, they are- therefore treatedin one of the two following ways.

1. The ore, being firft bruifed, is- to be verycarefully feparated from any intermixed particlesof galena and odier impurities, and is then to beroaft-cd, care being taken, efpecially in an aflayof blende, that the whole of the fulphur isdriven off. The roafted ore- is- now reduced tofine powder, together with half its weight of.charcord, and the mixture is put into an earthenretort, to the-beak of which a tube or adopter-is fixed dipping in water. Alter the retort withits contents has been expofed for about three-quarters of an hour to ahigh-heat in a windfurnace, it is to be cooled gradually, and on>breaking the veffel the zinc will be found con-creted in metallic drops in its neck.

2. The ore, after being prepared" and mixedwith charcoal, as above mentioned, is to- be-ftratified in a crucible with its own weight ofcopper- clippings; a perforated cover beingluted on, the crucible is to be kept at a cherryred or low white heat for the belt part of anhour, being then allowed to cool, its contentsare taken out and wafhed, by which the glo-bules of brafs are readily feparated from thelighter impurities. The excefs of weight whichthe brafs has over the copper employed, indi-cates the quantity of zinc abforbed from theore.

§.3. Reduliion of Ores.

The ore, whether calamine or blende, after

* Eergm. Opufc. ii. p. 338,