. HEtlNING OP LEAD. 213 



Thofe who are accuftomed to refine lead in the German 



method, will find no difficulty in following mine. For though 

 the cupel is made of fand inftead of afhes, there is no ditference 

 in the manipulations. 



We have (aen that the Enorjilli refine a crreat quantity of ^h's method ad- 

 , J r II t r^, r I I • 1 L J mits of keeping 



itaa on a imall ciipeJ. 1 he lame may be done in the metnod up xhe charge 



here defcribed, by adding in proportion as the lofs by oxida- <l«dng work, 



tion takes place, inippofing the capacity of the cupel to be 



tuch as to contain about five ton of lead, we might continue 



tlie o|)eration to three times that quantity in a fingle procefs, 



which would not have the inconveniences of the Englifli 



method. 



I flatter myfelf that a well-made cupel of fand may be ufed and the cupel 

 for feveral refinings, without requiring to be made up again S ^fj^^" ' 

 every lime like thofe of atlies ; but in thefe circumftances, and 

 before the lend is put in, it is neceflary to fill with well beat- 

 ten land the gutter or opening which was. before made for 

 carrying otf the litharge. Care muft be taken in doing this to 

 remove with a chitfel that kind of glaze which the oxide of the 

 lead leaves behind it. With this precaution, after wetting the 

 part where the new moiftened fand is to be applied, they will 

 (irmly unite together. 



From the long duration of the earthen floors of thofe re- 

 A erberatory furnaces in which lead ores and even litharge are 

 fufed, as was before mentioned, we have nc^ reafon to appre- 

 hend any bad confequences from the oxide of lead, which adts 

 only on the furface of the cupel, and penetrates to an inconli- 

 derable depth. 



After one or two refinings, this cruft of oxide may be taken Recovery of the 

 off and fufed in a blaft furnace, in order to recover the lead ; ''^^'^^^^^ ^^'^' 

 a procefs no lefs ealy than that of reducing the metal which 

 exifts in much greater quantity in the ordinary cupels. We 

 therefore obtain a larger quantity of litharge, which is one 

 advantage, and in addition to this, the lofs in iilver which ac- 

 companies the abforbed lead will be lefs. For in the fmall 

 quantity of precious metal which accompanies the oxide, it 

 is found by experiment, that the proportion is greater in the 

 abforbed lead than in that which is driven over in litharge. 



Infiead of fand we might make ufe of clay in conftru6tingToiwake the 

 our cupels, as is done in the hearths of the reverbatory fur-^"?^ d ff^d 

 uaces of Brittany j but it would then be necetfary to pound would be more 



ju expenflve and 

 kfs convenicttt. 



