1303
p^inary pots of cast iron, anil cast into sheets of varying thickness, according to the? s ure of the manufacturer. These sheets are made by pouring the melted lead upont * ! °'i plate placed over the boiler; and whenever the surface of the metal begins toa n ate , the l’Hte is slightly sloped to one side, so as to run off the still liquid metal,9til ’ !ave a lead sheet of the desired thinness. ■ It is then lifted off like a sheet of paper;c „ as the iron plate is cooled in water, several hundred weights of lead can be readily, 111 a day. In Certain white-lead works these sheets are one twenty-fourth of an' v uhi^' C k > * n others, hall that quantity; in some, one of these sheets takes up the whole1 of the conversion-box ; in others, four sheets are employed. It is of conse-
Ihei
Se nce not to smooth down the faces of the leaden sheets; because a rough surface pre-e{ j m ore points of contact, and is more readily attacked by acid vapors, than a polish-
V f i^' ese pHtes are now placed so as to expose an extensive surface to the acid fumes,a ,° ding each other over a square slip of wood. Being suspended by their middle, likei„ , of paper, they are arranged in wooden boxes, from to 5 feet long, 12 to 14ej _ es broad, and from 9 to 11 inches deep. The boxes are very substanlially construct-.their joints being mortised; and whatever nails are used being carefully covered.ho* e,r bottom is made tight with a coat of pitch about an inch thick. The mouths of theof are luted over with paper, in the works where fermenting horse-dung is employedfrom ■ tneans of procuring heat, to prevent the sulphureted anil phosphureted hydrogen* s . In jtiring the purity of the white lead. In Carinthia it was formerly the practice,Up . So in Holland, to form the lead sheets into spiral rolls, and to place them so coiledobv' 11 ^ le chests; but this plan is not to he recommended, because these rolls presentt^ phsly less surface to the action of the vapors, are apt to fall down into the liquid atare ott °m, and thus to impair the whiteness of the lead. The lower edges of the sheetshot ? Us l' eil ded about two inches and a half from the bottom of the box; and they must0llc h either one another or Its sides, for fear of obstructing the vapors in the firstli„ ’ °, r of injuring the color in the second. Before introducing the lead, a peculiar acidf„p 0r is Put into the box, which differs in different works. In some, the proportions are0 p r marts of vinegar, with four quarts of wine-lees; and in others, a mixture is madec ai .j' Ve ht5 r pounds of wine-lees, with eight and a half pounds of vinegar, and a pound ofUsij .“"ate of potash. It is evident that in the manufactories where no carbonate of pot-l u , ls employed in the mixture, and no dung for heating the boxes, it is not necessary to3 ‘hem.
lh e ’ mixture being poured into the boxes, and the sheets of lead suspended withinthe i’ ll, ey are carried into a stove-room, to receive the requisite heat for raising roundl |e at i corl '°sive vapors, and thus converting it into carbonate. This apartment isa si 2 „ "mmally by stoves, is about 9 feet high, 30 feet long, and 24 feet wide, or of such•j,, - as to receive about 90 boxes. It has only one door.
<! a y s ® beat should never be raised above 86° Fahr.; and it is usually kept up for fifteenlijr.p’ ln Which time the operation is, for the most part, completed. If the heat be toothe vapors too copious, the carbonic acid escapes in a great measure, and the\y, lc lead, less acted upon, affords a much smaller product.
\v as ben the process is well managed, as much carbonate of lead is obtained, as therec er 't'r'Pployed of metal; or, for 300 pounds of lead, 300 of ceruse are procured, besides aHot.' quantity of metal after the crusts are removed, which is returned to the melting-lias b b e mixture introduced into the boxes serves only once; and if carbonate of potash4 . yyj, 11 Us ed, the residuary matter is sold to the hatters,froo, .. ben the preceding operation is supposed to be complete, the sheets, being removedhot , e boxes, are found to havet grown a quarter of an inch thick, though previouslyS°ml. Ve a twelfth of that thickness. A few pretty large crystals of acetate of lead areCr Usl ll ? e s observed on their edges. The plates are now shaken smartly, to cause thel'trs> e ■ Ci,r bonate of lead formed on their surfaces to fall off. This carbonate is put intos bap e Clsterns ) and washed very clean. The cistern is of wood, most commonly of a squareb. H n’ n atl( l divided into from seven to nine compartments. These are of equal capacity,l'he re i, et l’! a l height, so that the liquid may be made to overflow from one to the other.s Ucc e J3 ‘f the first chest is too full, it decants its excess into the second, and so on inTh e !° n ‘ ® ee Rinsing Machine.
thtioi, r. V . ater P° u red into the first chest passes successively into the others, a slight agi-bon a u meanwhile kept up, and there deposites the white lead diffused in it propor-^ashino s “ l bat the deposite of the last compartment is the finest and lightest. After thisb'ate* S ’ T . white lead receives another, in large vats, where it is always kept under°h dryi n „ ‘ s lastly lifted out in the state of a liquid paste, with wooden spoons, and laidTh e wi' ta * , ' es t0 Prepare it for the market.
ll he nt sit te Iea| f °f the last compartment is of the first quality, and is called on the con-It is employed in fine painting.
"kite lead is mixed in equal quantities with ground sulphate of barytes, it is