Mr. H. L. Pattwson on Smelting Lead Ore, fyc. 177 



a good cupel, the second button of Silver will be exceedingly small, 

 and that it will be larger as these particulars have not been attended 

 to.. 



Where assays of Lead ore, for Lead and Silver, have been extensively 

 made, to determine the quantity of both metals which should be ob- 

 tained from the ore by melting and refining, the produce in the large 

 way has been found in most instances very nearly to correspond with 

 the assay after making an allowance on the Lead of 5 parts from the as- 

 say, or 1 cwt. of Lead for every ton of ore, as stated at Page 28, and 

 multiplying the quantity of lead indicated after this allowance, by the 

 proportion of Silver carefully determined by the assay. 



The loss of Lead in the refining and reducing processes, is usually 

 estimated, in the first instance, at one-twelfth of the quantity refined ; 

 but, when the deposit of refiner's fume is melted up, and the Lead 

 extracted from the test-bottoms and Litharge slag, the ultimate loss 

 becomes not more than one-fifteenth, and with some smelters one-six- 

 teenth of the original quantity. The loss sustained is least when the 

 refining furnace is worked at a low temperature, but it is not expe- 

 dient to reduce the test to the lowest degree of heat at which the oxy- 

 dation will go on, for, in this case, the Litharge, at the moment of its 

 formation, is not sufficiently fluid to allow the particles of Silver to 

 seperate from it, and combine with the remaining Lead in the cupel ; 

 they are thus, as it were, entangled in the Litharge, and carried with 

 it over the breast, by which the produce of Silver is materially dimi- 

 nished. 



Lowbyer, Alston, Sept. 5, 1831. 



