jBtt New Method of exlraBing Silver from 



of lead. The lead was again recovered with an increafe of weight, not yet fully amount- 

 ing to iper cent. The luork-lead contained in the centner two ounces, i//^ drachms of 

 filver, and hence in the whole 51 ounces, and one and ^V drachm. The whole quantity of 

 the copper-mat, divefted of its filver, in this operation, by means of lead, amounted to 

 9 centners of black copper ; hence one centner of black copper at 1 1 o lb. yielded 5 ounces, 

 5 and TT? drachms of filver. When the copper, obtained from this copper-ma":, was 

 examined, it was found to contain no more than jf^ drachms of filver, and, therefore, lefs 

 than is ufually the cafe with eliquated copper. 



^ more minute Explanation of this Pncefs, as performed in the large Way. 



Two conditions are eflentially requifite to the management of this procefs. (i) The 

 copper-mat muft have been roaftcd in the due degree. (2) The melting- furnace muft 

 have been fo conftrufted, that the copper-mat, while in fufion, may be enabled to pafs 

 through the body of the melted lead. 



The necelfity of the firft condition is evident from what has been already faid ; namely, 

 that when the copper-mat ftill contains too large a portion of fulphur not faturated with 

 that metal, part of the lead will be diflblved by the fulphur during the fufion, and an 

 irrecoverable lofs will be thus occafioned. On the contrary, when the copper-mat has 

 been too ftrongly roafted, it then no longer contains a quantity of fulphur fufficient to 

 hold all the copper in folution. Part of the latter will, therefore, feparate, and unite with 

 the lead. But it is better to fall into the lad error than the firft ; becaufe the copper can 

 be again recovered, when, as muft be done of courfe, the fcorise and litharge produced in 

 the refining of the lead impregnated with copper, together with the metal imbibed by the 

 aflies of the teft, are again reduced to the reguline ftate -, in which ftate they are conveyed 

 again into the furnace with a copper-mat lefs roafted. The fulphur of this laft again 

 feparates the copper from the reduced lead. But for the aecompliftiment of rifiis condition 

 it is neceflary, that by fmall experiments, eafy to be made, and in the manner indicated, 

 it fhould be firft afcertained, what degree of roafting of the copper-mat may be the moft 

 fuitable to the operation. And with this view the portion to be fubjefted to the trial 

 ihould be fo managed, that an uniform degree of roafting may be kept up. According to 

 my experiments in the fmall way, it feems, that copper-mat, which has been roafted the 

 third time in the ufual manner, and has once more pafled by itfclf through the melting 

 furnace. Is apparently the beft qualified for this purpofe, if pure lead be made ufe of 

 in divefting it of its filver. For though this laft fhould happen to take up fome of copper 

 ih the procefs, yet the copper may be recovered from it, by adding copper- mat of the 

 fecond roafting to the litharge, with the firft wafte and metallic portion abforbed by the 

 teft at the time when thefe produds of the refinery are afterwards reduced. 



Wc fee, therefore, that my method faves: (i) The expences of building and maintain- 

 ing the hottft appropriated to the procefs of eliquationj (2) The wages expended on this, 

 account; (3) The additional charges for the fuel in the operations of diquating, fecond 



eliquating 



