126 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA. 



but as the conditions attending this loss are dependent upon the quality of 

 the cupel and the character of the furnace and fire, it is not possible to ac- 

 cept the results obtained by them as applicable in all cases. Some exper- 

 iments upon the loss by cupellation were made for this investigation, as 

 nearly as possible under the same conditions as those existing in the assays 

 for the determination of small amounts of silver. It was found that when 

 the temperature was not too high for feather litharge to form and when the 

 draught was not too great, there was no perceptible loss of silver under .01 

 grain, which represents $1 to the ton of 2,000 pounds, notwithstanding 

 that this .01 grain was cupelled with 400 grains of lead. In fact, in most 

 instances, the button resulting from the cupellation of .01 grain or less of 

 silver with 400 grains of lead weighed from 0.5 to 10 per cent, more than the 

 actual amount of chemically pure silver cupelled with the lead. This ex- 

 cess is owing to the fact that the silver button obtained by cupellation is 

 never absolutely pure, but always contains from 0.2 to 5 per cent, lead, as 

 well as fine particles of the cupel. There is always a loss of silver in cu- 

 pellation, but as this loss rarely exceeds 1 per cent, of the amount of silver 

 present it can be entirely neglected in rocks containing less than Si to the 

 ton (0.002G5 per cent). This loss does not begin to be important until a 

 value of over $10 to the ton (0 0265 per cent.) is reached. When the con- 

 tents in silver is less than .01 grain, or less than $1 to the ton of 2,000 

 pounds, and the amount of lead alloyed with it 400 grains or less, the but- 

 ton resulting from the cupellation is invariably slightly in excess of the 

 actual quantity of silver contained in the alloy. With amounts of silver 

 exceeding .01 grain and lead exceeding 400 grains, up to a point where the 

 quantity of silver does not exceed .1 grain, the weight of the button does 

 not vary perceptibly, no matter what may be the quantity of lead (within 

 reasonable limits) used. At first sight it would appear to be inexplicable 

 that the quantity of lead did not to a greater extent affect the quantity of 

 silver obtained, but it must be remembered that the greater part of the loss 

 by cupellation takes place at the moment of "brightening," and that tin's 

 loss is directly proportional to the quantity of silver present. It is also 

 true that the greater the quantity of lead to be oxidized the greater is the 

 loss of silver. But this latter loss is so small in comparison with the former 



