CHAPTER XI. 

 ASSAYING. 



object of assaying country rock. — With a view to discovering, if possible, the 

 source of the ore in the mines of Em-eka District, numerous and careful 

 assays of all the different kinds of country rock in the neighborhood of the 

 ore bodies were made by the author. As the quantity of the precious 

 metals contained in any of these rocks is extremely small, it was necessary 

 to take unusual precautions in order to determine with any. degree of exact- 

 itude the amounts of gold and silver present. Assayers do not ordinarily 

 attempt to estimate with accuracy any values of either gold or silver less 

 than one dollar to the .ton (0.0001659 gold or 0.0026518 per cent, silver), 

 and as the country rock of this district never contains so much as this, 

 particularly delicate methods were required in the determination of the 

 actual quantities of these metals. 



Difficulty of obtaining pure lead. — One of the principal obstacles to be overcome 

 in obtaining satisfactory results in the assaying of all rocks containing very 

 small percentages of the precious metals, is the difficult)- of obtaining a 

 lead flux which does not contain very appreciable amounts of gold and sil- 

 ver. The purest litharge which it was possible to obtain from dealers con- 

 tained from 10 to 50 cents of silver to the ton of 2,000 pounds (0.0002652 

 to 0.0013259 per cent.), and as it was necessary to use from twice to three 

 times as much litharge as the weight of the material assa}'ed almost all the 

 silver obtained from assays of country rock made with such litharge came 

 from the litharge itself. 



Approximately pure litharge required. At fil'St sight it might Seem possible tO ob- 

 tain correct results by assaying the litharge separately and deducting its 

 value in silver from the value of the assayed rock. This is not practicable, 

 however, for the litharge of commerce is not only argentiferous but of very 



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