Z IN

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fition of tliis fub-oxyd is 88 of zinc to 12 ofoxygen.

4. Some experiments of Prouft f on the famefubjedt deferve to be cited. According to thisable chemift, 100 parts of zinc, by folution innitric acid, and fubfequent ignition afford 125 ofyellowifh oxyd. Alfo 100 parts of zinc whendiffolved in nitric acid and precipitated by car-bonat of potafh afford 180 of dry carbonat,which by calcination is reduced to 125 of mereoxyd. Hence according to both thefe experi-ments, oxyd of zinc is compofed of 80 zinc and20 oxygen.

5. According to Morveau the greenilh oxydformed by calcining the grey oxyd is compofedof 85 per cent . zinc and 15 oxygen y and

6. According to Wenzel the molt highly cal-cined oxyd of zinc confifts of 80 zinc and 2ooxygen, in which he perfectly agrees withProuft.

What conclufion can be drawn from thefevarious refults except the neceffity of freflrexperiments ?

The mutual adlion of zinc and water is veryconfiuerable. If pulverized zinc be moifteriedwith this fluid at the common temperature, themixture in the fpace of a few hours becomesblack, increafes in bulk, difeharges hydrogengas with a vifible effervefeenee, and at length isconverted into a greyifti-white oxyd. At a highheat the decompofition of the water is much■ more rapid, as we learn from an experiment ofHr. Prieftley’s; this philofopher having inclofedfome zinc in a glazed earthen tube heated itred, and then palled fteam over it; a largequantity of hydrogen was produced, and thezinc was converted into a dark coloured femi-tranfparent glafs.

The adtion of the alkalies is very linking,and was firft obferved with accuracy by lieLaffoneS. If filings of this metal are immerfedin ftrong and perfectly cauftic liquid ammoniaand a gentle heat applied, the mixture foonbecomes turbid and milky, a copious effervef-cence, probably of hydrogen gas, takes place,the odour of which is ammoniacal and alliaceous,the zinc is by degrees difiolved, and the folu-tion, during the effervefeenee, becomes of adeep black colour. The folution being com-pleted, a little black powder falls to the bot-tom, and the liquor after filtration is perfedtlyclear and of a yellow colour. If the zinc em-ployed is in the ftate of fublimed oxyd inlfeadof metallic filings, the liquor becomes fenfiblyhot, no gas is given out, and the folution is

f An. de Ch. xxxv, p, 53.

completed in a confiderably fhorter time thanwas required in the former cafe. Ammoniuretof zinc concretes by cooling and evaporationinto feathered cryftals> which are permanent inthe air. If the ammonia is fat-urated with zincthe folution is in part decompofed by water, awhite oxyd being precipitated; this howevermay be prevented by pouring in a little ammo-nia previous to the addition of water. No vifiblechange is produced by the addition of cauftiafixed alkali, but all the acids decompofe it,throwing, down the metallic oxyd :• with tinc-ture of galls a deep grey precipitate is produced:if a plate of copper is immerfed in the folution-the zinc is in part precipitated and the copperis diffolved, tinging the ammonia of a bluepurple colour.

The cauftic fixed alkalies a£l upon metalliczinc in nearly the fame manner as ammoniadoes, but according to De Laffone they areincapable of diffolving the fublimed oxyd. Thisis remarkable, for it- is certain from the experi-ments of Vatiquelin and others that- the oxydprecipitated from the falts of zinc is perfedtyfoluble in either potafh or foda.

Owing to the powerful affinity of zinc foroxygem it combines with the acids with greatreadinefs, forming a numerous clafs of falts,many of which are of importance.

Concentrated fulphuric acid when affifted byheat diffolves zinc either in the metallic ftate,or in that of oxyd, fulphurous acid gas beinggiven out in the former cafe. If the acid isdiluted with water it a£ts rapidly on zinc atthe common temperature, an abundance ofhydrogen gas being given out. The folutionwhen completed, and filtered to feparate a ftnallportion of infoluble black matter, affords, byevaporation and cooling, fulphat of zinc in theform of compreffed tetrahedral or hexahedralprifms terminated by tetrahedral pyramids.This fait if free from iron (which however itfeldotn is without particular precautions) isper-feftly colourlefs and tranfparent, it is mode-rately hard, and has a difagreeably ftypticmetallic flavour which remains long on thepalate. Its fp. gr. is 1.912. It is foluble inabout 2-f parts of water at 6 o°, and in a muchfmaller proportion of boiling water. It eftlo-refees by expofure to the air. In a dry heat itfirft melts in its water of cryftallization, and isreduced to an opake mafs, afterwards by ftrongignition it parts with mod of its acid in theform of fulphurous acid gas. It is decompofedin the moift way, with precipitation of its oxyds Mem. Sci. 177J.

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