132 SILVER-LEAD DEPOSITS OP EUREKA, NEVADA. 



collectively would weigh about 400 grains, were removed from the cupels 

 and placed in a scorifier in the muffle with 5 grains of borax glass. When 

 the mass was thoroughly melted it was poured into a mold and the lead 

 was again cupelled. The gold in the rock was all determined by concen- 

 trated assays in this manner, except when a series of assays were made 

 from samples taken near together. In this latter case the average value in 

 gold was determined by dissolving the whole number of the silver buttons, 

 use of assays. — While various purposes may be subserved by assays of 

 country rocks the main objects of those here described were first to ascer- 

 tain in which of the rocks the precious metals could be detected, and second 

 to trace the variations of tenor in different occurrences of the same rock. 

 As a qualitative method exception can scarcely be taken to the dry assay, 

 while even if the degree of accuracy reached in determining the absolute 

 contents in precious metals of the Eureka rocks has been overestimated, 

 the value of the results would scarcely be impaired ; for it will hardly be 

 denied that the results form a sufficient basis for a comparison of different 

 samples of the same rock all containing very small quantities of silver and 

 gold. For the purposes of this report it makes very little difference whether 

 a certain mass of limestone really contains 10 cents or 20 cents, if it can 

 be proved that a second body of limestone contains twice as much, or it 

 may be half as much. In other words the main purpose was to ascertain 

 the relative contents, not the absolute contents, of the samples assayed. 

 Even if the methods employed were ideally exact it would be impossible 

 to calculate the metallic contents of any large blocks of ground with pre- 

 cision, since it would be impossible to obtain samples which should correctly 

 represent the average of the mass. The following pages contain all the 

 assays of Eureka rocks, except those which were given in the chapter on 

 the source of the ore, as well as some special determinations which were 

 made of several minerals. 



