ASSAYING. 123 



Rozan method, containing about $1 to the ton (0.00265 per cent), was 

 cupelled on a fresh bone-ash test in an English refining furnace. The 

 first 300 pounds of litharge resulting from this cupellation ran very poor, 

 containing scarcely 2 cents to the ton (0.000053 per cent ). The litharge 

 which followed gradually increased in value until toward the last it con- 

 tained nearly as much as the original lead. This last litharge was reduced by 

 charcoal in a black-lead crucible, and the resulting lead was again cupelled, 

 yielding an excellent quality of litharge. Upon reducing and recupelling 

 the best litharge it was found that the percentage of silver was but little 

 reduced, showing that a point can be reached in the process of desilveriza- 

 tion at which it is not practicable to separate the silver from the lead by 

 cupellation. The refined litharge also contained a trace of gold, but the 

 quantity was so exceedingly small that it was neglected in the estimation 

 of gold values in assays of single samples.^ 



Assaying the litharge. — In assaying the litharge itself an interesting phenome- 

 non was observed. If the litharge was mixed with sufficient charcoal to 

 effect its reduction and the resulting lead was cupelled, it was found that a 

 very much smaller quantity of silver was obtained than if the usual flux, 

 consisting of bicarbonate of soda and bitartrate of potash, was used. To 

 what imperfection in the process this is due is not clear. The proportional 

 loss with ordinary litharge is much smaller than with that which contains 

 extraordinarily little silver. 



Experiments. — The following experiments illustrating the fact were made 

 in duplicate, in order that the results might be conclusive: (a) 800 grains 

 litharge were reduced with 600 grains bicarbonate of soda, 200 grains bitar- 

 trate of potash, and 200 grains borax. Silver resulting from cupellation, 6 

 cents per ton (0.0U0159 per cent.), (b) 800 grains litharge were reduced with 

 600 grains bicarbonate of soda and 200 grains, tartrate of potash. Silver 

 resulting from cupellation, 5 cents (0.0001325 per cent.), (c) 800 grains 

 litharge were reduced with 30 grains powdered charcoal and 200 grains 

 borax. Silver resulting from cupellation, trace, (d) 800 grains litharge 

 were reduced with 30 grains powdered charcoal. Silver resulting from 

 cupellation, trace. 



