Method to purify Lead.for AJfaying. 1$ 



found to contain too much filver. I therefore precipitated 

 another half pound of white lead by charcoal powder, after 

 the lead that fell from it had been feparated ; and then it 

 produced, by reviving, a mafs of lead without any mixture 

 of filver. 



Third Experiment. 



Cupels, employed for refining filver, imbibe about the 

 half of their weight of lead calx. One might therefore be- 

 lieve, that when this' lead calx is revived it would produce 

 lead free from filver. Befides the obfervation of others, 

 which confirms the contrary, I have made experiments with 

 the afhes of fuch cupels in which aflaying had been per- 

 formed with the utmoft accuracy ; but I found that the lead 

 thence made into ingots contained fometimes more than one 

 quarter of a grain of filver in the pound. The bone afties* 

 from which cupels are generally caft, are, by themfelves, 

 almoft infufible ; and this, on account of the great number of 

 fluxes which muft be employed to bring them to a fluid ftate, 

 makes the fufion of them difficult and cxpenfive. To four 

 parts of fine pounded cupel afhes, I put four parts of 

 potafh, four parts of fait, three parts of tartar, and one part 

 of clay, which mixed together produced, after being melted, 

 li- part of lead, making almoft 44 parts in the hundred *. 

 But this ftill contained the above-mentioned quantity of 

 filver, and could not therefore be proper for the propofed 

 end. 



As the two firft-mentioned experiments will completely 

 anfwer the purpofe, it is perhaps unneceflary to feek for 

 other methods ; as it will be hardly poffible to find any lefs 

 complex, or eafier to be put in practice. 



• There mud here be an error in rhe original. Inftead of rjpart of 

 'ead, we ought, perhaps to re id \ 



IV. On 



