2l5 'Memoir oti the Rrfunng of Lead',. 



houfcp, it would remain chargol with a great deal more, 

 which would render it more difficult to proceed to a fecond 

 operation, called the refining of fiver, by which it is carried 

 to the required degree of purity. Tlie Germans call this fe- 

 cond T()rocith fiber brennen, burning filver. 



Thofe accuftomcd to the refining of lead according to the 

 German method, will be able to perform that which I here 

 propofe ; for, though the cupell be of fand inftead of afhes, 

 the operation niuft be conduced in the fame manner. 



It has been fcen that the Englifii refine a large quantity of 

 lead in a fmall cupel! : in the like manner, a great deal of 

 metal may be made to pafs by that which I propofe, if care 

 be taken to add more metal as that which is oxidated efcapes. 

 If we fuppofe that the cupell is capal)le of containing four or 

 five tons of lead, above fixteen niav be refined at one opera- 

 tion ; which will not be attended with the inconveniences of 

 the Englilh procefs. 



I ha«e reafon to think that a cupell of fand well con- 

 ftruAed may ferve for feveral operations without the neceffity 

 of re-conftrufting i: each time, as is the cale with thofe of 

 aflies ; but in this caic, and before the lead is Introduced, 

 you mud fill up the gutter which has been m^/:Ie for the 

 litharoe to run off, after having removed with a chifel the 

 kind of varnifli which the oxide of lead has left on the fides 

 of it, in order that the new fand, fomewhat tnoifteucd, may 

 form an intimate connc6lion with the old fand, which mull 

 alfo be watered in that part before the new fand is depofited. 



The long duration of earthen foles in reverberating fur- 

 naces, where lead ore and even litharge are fufed, as I have 

 already mentioned, leave? no room for apprehenfion in regard 

 to the aftion of the oxide of lead, which will aft only at the 

 furface of the cupell, and will penetrate only a very fmall 

 part of its thicknefs. 



After one or more operations of refining, this cruft muft 

 be removed, and fufed in a furnace in contaft with fuel, in 

 order to obtain the lead. This procefs will be as eafy Ss the 

 reduction of that metal contained in the aflies of common 

 cupclls, and in a much fnialler quantity. More litharge then 

 will be obtained by the new method than the old ; which is 

 an advantage, as I have already obferved. I (hall here add, that 

 as the folc of land does not abforb fo much oxide of lead as 

 that of aflies, it will not carry with it fo much filver; for it 

 is well known that lead revived from its aflies aUvavs con- 

 tains more than that which arifes from the redudlion of 

 lithanre. 



Inllead of fand, argillaceous earth might be employed for 



the 



