BS Method to purify Lead for AJJaying. 



with thefe noble metals, that after being (melted it eannot 

 be employed for the above purpofe; and though there be 

 lead ore which exhibits only a very few or no traces of their 

 prefence, and in the firft cafe the proportion mull never be 

 more than a quarter of a grain in the pound [mark), it is 

 exceedingly rare in the common courfe of mining to find 

 pieces of fuch a nature, and people often have not leiiure to 

 fearch for them. As I have fometimes been expofed to 

 great inconvenience for want of a proper piece of lead, I 

 endeavoured to find out an eafy method of procuring, with- 

 out a tedious procefs, fuch a quantity of pure lead as would 

 be furficient for the before-mentioned teft ; and as I do not 

 Temeinber to have heard of its being any where defcribed or 

 employed, I have reafon to think that an account of it may 

 be of fome ufe, at lead in the art of allaying, in cafe a more 

 extenfive application of fuch a fmelting procefs be not pof- 

 fible on a large fcale, or if it fhould not be found profitable. 

 When one begins to reflect on this object, the firft idea that 

 occurs is to accomplifh the end in view, by diflolving the 

 lead in an acid, and then precipitating either the lead or the 

 finer metals ; but on clofer examination there is no procefs 

 of this kind which will not be either too expenfive, when it 

 is neceflary to prepare feveral pounds at once, or require 

 longer time than one can poflibly bellow. For thefe reafons 

 J gave up this method, and adhered to that only which was 

 performed merely by fufing in a crucible with the afliftance 

 of a requifite degree of heat. 



Firft Experiment, 



Litharge, a cheap article that can be eafilv procured, was, 

 the firft i'ubftance with which I thought it neceflary to make 

 experiments. As itfeemed poflibie that il might be free from 

 any mixture of filvcr, that circum fiance was firft examined 

 before I proceeded further. I then melted fome ounces of 

 Jitharge with equal quantities of pot-alh and tartar; but the 

 iead obtained from this mixture contained (till about half a 



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