14 Method to purify head for AJfaying. 



tained, which weighed 23 ounces, was found to contain lefs 

 than i grain of filver in the pound. In the fecond mafs 

 there was found fomewhat more than fix ounces of lead, 

 which contained all the filver that had been before mixed 

 with the litharge, becaufe in the lead which had been re- 

 duced from the litharge in the above manner there were 

 no perceptible traces of filver. This lead was then melted 

 over a flow fire, and caft into bars, which were rolled fmooth 

 and formed into mafles of a known weight, to be ufed for 

 affaying gold and filver, and for other purpofes of the fame 

 kind. All thefe meltings were made in one crucible, which, 

 according to every appearance, remained unhurt. If the 

 fame experiments were made with red lead, the like refult 

 would infallibly follow. 



The caufe of this procefs, and of the effects thence pro- 

 duced, is, that when lead, which contains a fmall quantity of 

 filver, is calcined and brought into the ftate of litharge, the 

 filver in it, if not fcorified, is diffufed in infinitely fine par- 

 ticles, fo that it is impoffible for it to fink through the melted 

 litharge and fettle at the bottom. When the lead calx is 

 revived on the furface, the leaden grains, as they are formed, 

 fink down through the litharge, and carry with them the 

 fcattered grains of filver, in fo far as this leaden fhower, if 

 I may fo name it, is compact and powerful enough to col- 

 lect them. Were the opinion of thofe juft, who affert that 

 a calx of lead free from filver, when revived by tartar, ac- 

 quires again, by the creation of new filver, a portion of that 

 metal, litharge ought not to be revived by tartar, or any 

 thing of the like kind from the vegetable kingdom; but on 

 this occafion I found no fuch effect produced. 



Second Experiment. 



With the fame view of obtaining lead free from filver, I 

 melted, in the like manner, half a pound of white lead, 

 which produced half an ounce of lead. When the litharge 

 {landing over it was revived, the lead obtained w r as ftill 



found 



