the Sulpkureotiscne of Copper by Ltad. i^g 



In this^ operation, their volume will amount to 760 cubic Rhinland inches; and hence if 

 the perpendicular height of thefe three centners of lead (hall be 6 inches in the outward 

 hearth, it follows, that the breadth of this hearth muft be 9 inches, and its length a little 

 more than 14 inches. 



In performing the procefs, the furnace is previoufly heated to a fufficient degree, and the 

 lead afterwards introduced on the outer hearth; becaufe the heat is there fufhciently in- 

 tenfe to fufe it. Its furface is fecured againft oxidation, by covering it with powdered 

 charcoal. At the fame time the furnace is charged with copper-mat, and the requifitc 

 quantity of coals, and the fufion effefted by a clear fire. As the operation proceeds the 

 lower part of the copper-mat ifluing from the furnace through the aperture («), and rifing 

 through the body of the lead to its furface, is farther prevented from cooling, by means of 

 fome pieces of burning wood. The beft and moft ufeful proportion of the coal, to that of 

 the copper-mat in this fufion, muft be determined by experience. 



The copper-mat being now deprived of its portion of filver, and flowing into the fore- 

 pot (vortiegel) from above the lead in the outer hearth, is once more roafted, previous to 

 cxtra£ling the copper. But it is to be obferved, that by this method of divefting it of its filver, 

 it at the fame time undergoes a farther roafting; on which account another part of the 

 expence is faved in my procefs. 



In the management of this procefs, it is evident, that as much copper-mat as may be 

 thought fit, can be decompofed by the fame individual quantity of lead; and accordingly, 

 that this laft may be impregnated with filver at pleafure in various degrees. It is not ad- 

 vifeable, however, to alloy the lead wdth too great a proportion of filver ; becaufe a fmall 

 lofs of the compound metal would then produce a more confiderable lofs of filver. But I 

 muft leave this to the judgment of the artift, and to future experience. 



When the lead is to be run off, the receiver muft be firft duly heated, and then the 

 tap hole opened. The whole of the lead is thus drawn off from the outer hearth of 

 the furnace, and its furface covered with charcoal-duft. Frelh lead may then be again 

 conveyed, after ftopping the tap-hole, into the cuter hearth, and the operation continued 

 as before. 



Whenever the furnace requires to be cooled by the blaft of the bellows, the work lead* 

 is firft entirely dravra off from the outer hearth, and alfo laded out of the draining hearth; 

 after which, all the copper-mat that remains in the outward hearth, and in the furnace, is 

 fuffered to run into the draining hearth, now cleared of the lead. But this copper-mat, 

 not being yet deprived of the filver it contains, muft be added at the next charge of the 

 furnace. 



The lead, which is thus alloyed with filver, is at laft fubje£led to cupellation in the 

 ufual way. The litharge, which is obtained in this operation, the metal abforbed in by 



• Work-lead, or lead freed from copper, and mixed v/ith filver by the operation. See Crttft Principlet 

 efChemifry, § J4.7S, i486.— -Tranll. 



the 



