Mr. H. L. Pattinson on the Smelting of Lead Ore, 8(c. 167 



But this quantity of Lead can never be obtained from it by assaying in 

 the dry way. With great care, as far as 8*2 or 83 per cent, of Lead may 

 be obtained from a very pure piece of cubical Galena, by treatment with 

 borax and tartar, in the hands of an experienced assayer. In the large 

 way Lead ore is seldom dressed quite pure, and does not often yield more 

 Lead to the assay than 77 or 78 per cent. Ore, assayed to yield 77 per 

 cent of Lead, contains, besides, probably, 4 or 5 per cent., which is oxy- 

 dized, or volatilized, before reduction in the process of assaying. In 

 estimating the value of a sample, reference is only made to its absolute 

 produce by assay, no regard being paid to the probable quantity of lead 

 it may contain, beyond the assay produce. 



It is never expected, in the large way, to obtain the quantity of metal 

 indicated by the assay, but some ores in smelting approach much nearer 

 to it than others. A customary allowance is to deduct 5 parts from the 

 assay produce of 100 parts of ore, which is equivalent to making an al- 

 lowance of 1 cwt. of Lead for every ton of ore. Besides this, an allow- 

 ance of 2 or 3 per cent., or more in wet weather, must be made for 

 moisture in the ore, when weighed over at the mine, as the sample as- 

 sayed is, in all cases, perfectly dry. It is found, in practice, in almost 

 every case where a large quantity of well-dressed ore is skilfully and 

 carefully smelted, that the allowance of 5 parts of Lead from the assay, or 

 1 cwt. of lead for every ton of ore is rather more than sufficient to cover 

 the loss in the smelting process, without taking into account the Lead 

 obtained from the hearth-ends and smelter's fume. 



REFINING OF LEAD. 



The quantity of silver contained in the greater part of the Lead raised 

 in the northern mining district, is sufficient to render its extraction pro- 

 fitable, and it is of the greatest importance that the process of refining 

 should be performed in the most perfect and economical manner, in con- 

 sequence of the enormous quantity of lead continually submitted to this 

 operation. It is well known that the separation of Lead and Silver is 

 effected through the difference of oxidability between these two metals, 

 silver remaining unaltered when exposed to the air of the atmosphere at 



vol. 11. t t 



