C O A

COB

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this advantage, that the fulphur is at the fametime entirely got rid of, which cannot be done byclofe diftillation, and in confequence the fuel ismuch better fitted for thofe purpofes in whichthe prefence of fulphur would be detrimental:for this reafon doubtlefs it is that all the coakconfumed in the numerous iron forges of thiscountry is thus prepared. Another method ofcharring coal is to burn it in large vaulted ovenstill it ceafes to flame: this is more economicalthan the former, both becaufe the produdt ofcoak is greater, and becaufe the flack or fmallcoal of the caking kinds may be employed forthis purpofe ; all the volatile parts however areloft, and the coak is not entirely defulphu-rated.

In the county of Saarbruck on the Rhine , arefome eftablifhments for making coak and lamp-black at the fame time, which perhaps mightbe found worthy of imitation in this country.The furnace c is a long cylinder of brick-workplaced fomewhat in a flanting direction, ter-minated at the lower-end by a grate and regifterdoor, and opening at the other extremity into alarge vaulted chamber: the firft chamber com-municates with a fecond fimilar to it, exceptthat it is fmaller, and this latter by means of anaperture in the ceiling opens into a chimney, afack of loofely woven cloth being interpofed.The procefs begins by lighting a fire in the fur-nace and fupplying it gradually with coals, tillthe furnace is about half full, then by meansof the regifter in the door, a fmall current ofair is admitted till the coals ceafe to fmoke; atthis period the door is opened and the contentsof the furnace are raked into a hole below itsmouth, where they are extinguifhed, leavinghowever in the furnace a fufficient quantity oflighted coals to kindle the next charge. Whilethe coals are thus charring the fmoke paffes in-to the large chamber, where it depofits thegreateft part of its foot, and the reft is collectedin the fmall chamber, and in the fack whichcovers the opening into the chimney. By acareful regulation of the draft it appears pro-bable that the coal might be as completely de-fulphurated, and with as little lofs as in the openair, and tire lamp-black would be nearly a cleargain : ioo lbs. of coal thus treated afford about33 lbs. of coak, and 3A of lamp-black.

Coal, when heated in clofe or nearly clofeveffels, affords a vaft quantity of a highly in-flammable gas (already defcribed as a variety ofCarburetted Hydrogen) of Coal-Tar , orPetroleum, and of impure carbonated am-

monia. From a laudable defire of faving thetwo latter valuable produces, which had hithertobeen allowed to efcape in the procefs of coak-ing, Lord Dundonald creeled fome years ago atCoalbrook-dale, and we believe elfewhere, aferies of buildings to ferve as a kind of diftil-Iatory apparatus, in which he prepared coak, andat the fame time collected the petroleum and am-monia difengaged in the procefs: his fuccefs wascomplete, as far as the diftillation was con-cerned, but the undertaking was fliortly aban-doned in confequence, as we underftand, of thefulphur contained in coak thus made, whichrendered it unfit to be ufed in the furnaces.Indeed it is manifeft, that in order to decom-pofe the pyrites with which all coal more or lefsabounds, it is neceffary to expofe it while burn-ing to fuch a ftream of air as ftiall deftroy boththe petroleum and ammonia, and leave no oppor-tunity for the exertion of economical ingenuity,except in the colleblion of foot and increafingin fome degree the product of coak.

COATING , or Lorication. See Cements.COBALT. Cobalt , Fr. Kobolt , Germ.

Cobalt when pure is a metal of a whitecolour inclining to bluifti or fteel-grey, whentarnifhed acquiring a reddilh tinge : its fractureis compact, fine-grained uneven. At the com-mon temperature it is brittle and pulverizable,but when red hot will bear to be in fomedegree extended under the hammer. Its fpe-cific gravity is—8.53. It is attracted by themagnetic needle, and is itfelf capable of polarity.It requires for its fufion nearly the fame inten-fity of heat as call iron does. When in theftate of oxyd it tinges the faline vitreous fluxesof a deep blue colour. It is foluble in nitro-muriatic acid, and the diluted folution forms ablue fympathetic ink. It occurs, 1. mineral-ized by arfenic; 2. as an oxyd; 3. combinedwith arfenic acid4. combined with fulphuricacid.

Sp. I. Arfenical Cobalt. a

Cobalt is never found pure in the metallicftate, but is always alloyed with arfenic, andoften contains befides a variable portion of ironand fulphur, befides which it is occafionr.liymixed with nickel, bifmuth and fiver. Theamorphous fub-fpecies have none of them beenfubjefted to an accurate analyfis, hut the crys-tallized has been examined both by Klaproth and Taffaert. The former chernilt obtained,from the bright white cobalt of 1 unaberg.

(3d fub-fpecies)

c Joum. des Mines. No. 35, p- 487.

Emmcrling, Widcnmann.Hauy, Kirwan, Eroclunu.