306 MINING INDUSTEY. 



The cupelling furnace is of the kind commonly used in England. Figs. 

 9, 10, and 11 on Plate XXV show the method of its construction. Fig. 9 is 

 a side elevation ; Fig. 10, a horizontal section on the line A B o{ Fig. 9 ; 

 and Fig. 11 is a vertical section on the line C D of Fig. 10. Fis the fire- 

 place ; G, the ash-pit ; H, the bridge ; /, the test-ring or hearth ; J, the 

 tuyere ; k, k, supporting and adjusting screws for the test-ring ; L, the flue 

 leading to the stack, M; iV, a melting pot or pan in which the metal may 

 be prepared for the hearth. 



The hearth consists of bone-earth, prepared from the bones of cattle, 

 which lie in profusion along the track of the old emigrant road, furnishing an 

 abundant supply. The bones are burned and then pulverized in the stamp 

 mill ; and being moistened with water that contains a little alkali, leached 

 from wood ashes, the mass is beaten compactly into the test-ring. This is 

 oval in form, being 4 feet long by 3 feet wide. It is a rim of iron, 7 or 8 

 inches deep, having bars across the bottom to sustain the hearth of bone- 

 earth. The latter being prepared in the rim it is very carefully dried, and 

 the ring is then introduced into the cupel-chamber, supported upon screws, 

 by means of which it may be elevated or lowered, or inclined in one direc- 

 tion or another. When properly adjusted, it is heated, very gently at first, in 

 order to avoid cracking. The heat from the fireplace, passes over the bridge 

 into the cupel-chamber and thence by the flues to the stack. When the 

 hearth is well heated the lead is placed upon it and a blast of air is introduced 

 by means of a fan-blower and tuyere. This acting upon the surface of the lead, 

 the metal is oxidized, and the resulting litharge is allowed to run off" through 

 gutters made for its passage, in the surface of the hearth, into vessels placed ? 



below for its reception. As the lead is gradually oxidized, fresh supplies of i 



metal are introduced, either in the form of pigs, or in a molten state, the pan, 

 N, being provided for the purpose of fusing the metal, if desired. By this 

 means the metal on the hearth is constantly enriched ; and when the button ^ 



of accumulated silver has become as large as may be desirable, the addi- 

 tion of lead is discontinued and the oxidation carried on until the lead is 

 nearly all removed, leaving a mass of silver, of a high degree of fineness, 

 upon the hearth. The litharge ])roduced by this operation contains some 



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