Z I N
z r n
( 504 )
liy all tlie alkalies, either cauftic or carbonated,and by all the alkaline earths. The proportionof its component parts is very varioufly hated.According to Bergman* 1 ioo parts of the crys-tallized fait lofe 4° by gentle calcination, whichare therefore water ; the refidue after beingkept white hot for three hours was reduced to2® parts of a greenifh-grey colour which -wasoxvd of zinc, the acid haying been driven off.Train thefg .data fulphat of zinc confifts ofgo. Oxyd of zinc4.0 Sulphuric acid40 Water
100
•But according to Mr.. Kirwan’ too parts offulphat of zinc by a heat of 376° lofe 39 whicharc water, and a funilar quantity of the famefait afforded with muriat of barytes 61.24 ofignited fulphat of barytes. But the compofitionof fulphat of barytes is varioufly flated. Klap-roth , Black and others reckoning the amount ofacid in this fait to be 33-33 percent, whereasMr. Chenevix eftimates it at no more than23.5. Hence the compofition of fulphat ofzinc as found by Mr. Kirwan’s analyfis may bereckoned at
39. Water
20.4. or 14.3 Sulphuric acid40.6. or 46.7 Oxyd of zinc
Mr. Smithfon k again, from feme Ample andapparently accurate analyfes reckons the com-ponent parts of dry fulphat of zinc to be50 Sulphuric acid50 Oxyd
.too
The fait called in commerce White vitriol isan impure fulphat of zinc of a bluifh-whitecolour with ochery llains externally ; it has agranular cryftalline texture like loaf l'ugar, andis in irregular lumps and maffes. It is preparedlargely at Rammelfberg and elfewhere in Ger-many by roalling blende and then expofing it tothe air j the fulphats of zinc, lead, iron andcopper that are thus formed, are feparatedfrom the earthy parts by lixiviation, and theliquor being boiled down till a fhrong faline pel-licle forms on its furface is let out into cryftal-fizing vats where it concretes into hard granu-lar maffes. The Eriglifh white vitriol is pre-pared for the moll part by direct folution of
metallic zinc in fulphuric acid, and is thereforepurer than the foreign, though it ftill containsa very notable quantity of iron. Both kinds maybe confiderably, though not entirely, purifiedby folution in water, and then abandoning theliquor to fpontaneous evaporation in an openveflei containing fome granulated zinc: thefulphat of lead will fubfide to the bottom, andother foreign fulphats will be decompofed bythe metallic zinc. The faline mafs when dryis to he lixiviated with cold water and the clearfiltered folution, after due evaporation, will.afford regular cryftals of fulphated zinc.
Sulphite of zinc is prepared by putting fomeoxyd of zinc and water into a Woulfe bottle,and throwing in fulphurous acid gas till theoxyd is diffolved. The fait -thus formed cryf-tallizes by gentle evaporation. It has a ftypticfulphureous flavour: it is eafdy foluble inwater, but not at ait fo in alcohol: it is decom-pofed by the other acids with effervefcenceowing to the efeape of fulphurous acid gas ; itforms white precipitates with the alkalies whichare entirely re-foluble in cold dilute fulphuricacid: by expofure to the air it is foon convertedinto the fulphat.
If fulphurous acid is digefted upon metalliczinc inftead of the oxyd, an immediate andrapid a£tion takes place between them muchheat is difengaged, fulphuretted hydrogen gasis produced, the fluid becomes of a turbidbrown or yellow colour, but grows clear inproportion as the faturation advances. Thefluid thus produced has a remarkable pungentftyptic and fulphureous flavour: when gentlyevaporated it becomes thick like fyrup, and thendepofits' acicular tetrahedral prifms terminatedby very acute tetrahedral pyramids ; thefe whenexpofed to the air become efflorefcent, and areflowly decompofed into a mixture of fulphat ofzinc and fulphur. . Before the blow-pipe thisfait gives out a vivid light like zinc in corn-bullion, and throws out on every fide arboref-cent and tubercular ramifications. The fulphu-ric and muriatic acids decompofe it with effer-vefcence, fulphurous acid gas being given out,and a yellowifh-white powder being precipi-tated. Nitric acidalfo fets at liberty fulphurousacid, and throws down a flocculent duftile andadhefive precipitate which is fulphur. Whendiftilled per fe in a retort it affords water, ful-phurous and fulphuric acids, fublimed fulphur,and there remains behind oxyd of zinc with alittle fulphat. By digeftion with alcohol it is
ranf, 1803. p. 13, 1 Fourcr. Svfi. des Connaiff. v. p. 380.