ZIN

Z 1 N

( 501 7

being raifed from the mine, is fir ft: d re fie cl, thatis, it is broken to fmall pieces, and the galena,pyrites, and other impurities are feparated asaccurately as poffible by hand; it is next cal-cined at a moderately red heat in a- reverbera-tory furnace, by which the- calamine is deprivedof its carbonic acid, and the blende of the modpart of its fulphur. It is then waflied, by whichthe lighter earthy parts are feparated from themetallic oxyd, which latter, being dried, is inti-mately mixed with about | of its weight ofcharcoal by grinding the ingredients together ina mill,, and is now ready to be fmelted. Thefurnace in which the reduddion is performed isa circular one not unlike that of a glafs-houfeyin it are fixed fix large earthen pots, about fourfeet high, and nearly: of the fame fhape as oiljars : into the-bottom of each pot. is inferted aniron tube that pafies through the arched floorof the furnace, and dips in a veffel of waterplaced beneath, while the other end of the tuberifes within the crucible to within a few inchesof its top. Thefe crucibles are filled up to thelevel of the tube with the mixture of roafted oreand charcoal,, the cover of each is very accu-rately luted on, and the furnace is charged withfuel, by which an intenfe heat is kept up forfeveral hours. The 2 inc, as it is reduced,afeends to the top of the pot in die form ofvapour, and there being prevented-from el’capingby the cl'ofely luted- cover it defeends throughthe central iron tube, whence it pafies into thewater, and is there condenfed in imail drops.Thefe globules are afterwards melted and callinto ingots, in which ftate they are brought tomarket.

Common zinc generally contains a little lead,copper,, arfcnic, iron, manganefe, and probablyplumbago, which often confiderably impair thequality of the alloys into- which it enters. Inorder to get rid, in part at leaft,, of thcle impu-rities, the common practice is to melt the zincin a crucible, and then to iiir into it, by meansof a flick or earthen nod, a mixture of fulphurand fat: the latter of thefe preferves the zincfrom oxydation, while the former, uniting withall the metals prefent, except the zinc, convertsthem into fulphurels, which rifing to the topform a icoria that may be fkimmed off: this isto be repeated as long as any fcoria makesits appearance. M. Prouft objefts to thismethod as completely ineffedlual and propofesanother, which is fimply rediltilling the zinc inan earthen retort; after the metal has paffedover there remains behind a ' mixed mafs ofoxyds and other impurities. But it is not very

obvious how either the arfenic or lead carrbe thus got rid of, nor does it by any means ap-pear that the old method is fo very nugatory.It would probably be an improvement firft toheat the zinc nearly to melting, in which ftateit is very eafily pulverizable, and having thusreduced it to fine powder, to mix it with about

of its weight of fulphur and a little pitch,then to charge an earthen retort with the mix-ture, to keep it for fome time at a temperaturenot exceeding that of melted lead, and then to-raife it by degrees till the zinc begins to bevolatilized : the contents of the retort beingnow allowed to cool gradually, the purifiedzinc would be found at tire bottom,, covered bya fcoria of fulphuret.

If however the zinc is required of extremespurity, take the common fulphat of zinc (whitevitriol of the fhopsj diffolve it in hot water, andadd a little fulphuric acid and granulated zinc,,by this means the copper, arfenic, and the prin-cipal part of the iron will be precipitated.When the acid is faturated pour off the clearliquor, and evaporate it- to dry net's ; moirten thewhite: fait thus procured with a little nitricacid, and heat it nearly to rednefs in a crucible ;by this the refidue of the iron and manganefewill he reduced to the ftate of infoluble oxyd,and. warm water will take up only the purefulphat of zinc. This is to be decompofed bycarbonat of ammonia, and the white precipitatethus obtained, after being waihed and calcined,is to be mixed with about ■£■ of charcoal, andreduced by diftillation in the ufual way.

§. 4 . Ph'jftca ! and Chemical Properties.

The colour of zinc is bluifh-white with ahigh metallic luftre; its texture is betweenhackly and foliated, that is to fay, the plates ofwhich it confifts inftead of being fmooth likethofe of bifmuth or antimony, are covered witha multitude of fmall points which render itpeculiarly harfli to the touch. In thin plates itmay be broken without difficulty, but in doingfo a kind of refiftance is perceived, as if the fa-cets of which it is- compofed adhered to eachother not merely by the appofition of their lur-faces, but by the- mutual penetration of thofelittle points with which, when feparated, theyappear to be covered. The larger ingots cannotbe broken but by means- of iron wedges. Zincat the common temperature poflefles a moderatedegree of dudlility, and may be laminated bypalling through rollers into plates of conflcle-rable thinnefs and elafticity. With care itmay be drawn into wire, the tenacity of which,