122 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA. 



Different kinds of lead. — White lead (carbonate of lead), sugar of lead (acetate 

 of lead), and the best granulated lead ordinarily contain upwards of ten 

 cents to the ton (0.000265 per cent.), and although any of them may be 

 used in assaying rocks containing less than 50 cents to the ton (0.001325 

 per cent), yet the results obtained are more or less uncertain, and are not 

 at all to be relied upon in very poor rocks, such, for instance, as carry 

 below 10 cents to the ton (0.000265 per cent). Moreover, the carbonate 

 of lead, owing to the carbonic acid it contains, is liable to boil over in the 

 crucible, though this can be obviated by a previous calcining. A like ob- 

 jection can be made to the acetate, the acetic acid of which contains more 

 carbon than is needed to reduce the oxide of lead. If it is used in its 

 natural state it swells up, and after the acetic acid is decomposed the resid- 

 ual carbon thickens the slag and prevents the proper settling of the globules 

 of lead which everywhere permeate the mass. This difficulty, however, 

 can also be remedied by a previous calcining. Granulated metallic lead, 

 though otherwise unobjectionable, melts too quickly and unites at once in 

 a mass at the bottom of the crucible, thereby preventing every particle of 

 the powdered rock from coming in direct contact with it; and although 

 such an intimate contact is unnecessary in assaying ordinary ores, it is 

 found indispensable where the material to be assayed contains such ex- 

 tremely small quantities of the precious metals as do the ordinary country 

 rocks of a mining region. 



oxide of lead required in the siag. — It has been remarked that the slag is the better 

 for the presence of oxide of lead. This is notably the case when the rock 

 treated is silicious, as in combination with other bases it renders the silicate 

 formed more fusible and liquid. Litharge seems also to attack quartz more 

 energetically than even soda or potash. Even in those rocks which con- 

 tain scarcely anything but carbonate of lime it is found to assist in the 

 formation of a proper slag. 



me process adopted for making litharge. — The litharge used in assaying all the Eu- 

 reka rocks, as well as those of the Comstock, was made at the refining 

 works of the Richmond Company in Eureka. The following process was 

 adopted in manufacturing this litharge. One thousand pounds of market lead 

 the refined lead obtained from the parting of silver and lead by the Luce & 



