i08 Refining op ieaD, 



/oM portion of time and fuel; befides which, the lofs jn re* 



covering the lead by fufion of the cupel is very expenfive and 



the proda6t lefs confiderable than in the common way. The 



Oxide of lead obtained in this laft method may be eafily fufed, 



and reduced if needful ; but it is an article of value in the 



art*?, and therefore very acceptable in the market in its flate 



of oxide. 



iTeflels of cby The lead ores and litharge may be fufed as is done- in Eng- 



fcad.*" "^^ '"^land and Britanny, in a reverbalory furnace, of which the 



floor or bafon is formed of moiftened and rammed clay. Thefe 



floors refift the a61ion of fire as well as that of the oxide of 



lead during fix or eight months confl^ant work. 



Thefe are appH- The durability of thefe bafons of earth firft gave me a no* 



cable to refining. jJq„ of the method I fliall propofe for refining furnaces, irt 



which the intention is to oxide the lead in order to oblain li*. 



tharge, and not to caufe it to be totally abforbed in the cupels, 



as is done when the metal is aHTayed, to fnew how much lilver 



it contains. 



It wduld be pre- In the operation upon a large fcale the cupel, though af 



ferable that no jjQ^^g abforbs Only part of the lead, as I have already remarked, 

 ablorption took , . . , /• • i • i , i , , 



^lace. obfervmg at the lame time that it would be much more ad^ 



vantageoUs to obtain the whole converted into litharge, of 



which the redu6lion into lead is infinitely more eafy than that 



of the oxide contained in the aflses, which refift fufion, and 



aflford a fcoria that always contains fome metal. i 



EnglilTi procefs. Upon a cupel of atbes rammed into an ovfil ring of iron, 



fsz tons of lead ^bout five feet in length aixl three and a half in width, the 



arc oxided with „ ,.^ ^ . ,- ^, , . i . r i i i • i 



fcarcely any ab- Englifii refine m luccefl) on about twelve ton ot lead, which 

 lorption, becomes converted into fine merchantable litharge, with the 



exception of the fmall portion that penetrates the cupel, of 

 which the thickiiefs is lefs tlian three inches. This cupel is 

 fupporled under the roof of the furnace by two bars of iron. 

 The litharge is driven by thfe blaft of bellows towards the an- 

 terior part of the furnace, -whence it falls without interruption 

 upon the area of the fouridery ;- and, at the fame time talupply 

 the fpace which this fubirAflioii of oxide would leave, a pig 

 of lead is gradually a'dv4an<?ed into the ihlerior of the. furnace, 

 placed on one fide of the nozel of the bellows. This lead, 

 by its gradual fufion, keeps the cupel full till towards ihe end 

 of the operation. 



3 I have 



