302 MINING INDUSTET. 



elevation ; Fig. 3 a horizontal section through A B ; and Fig. 4, a vertical 

 section through C D of Fig. 1. The total height of the furnace is about 40 

 feet. The hearth is built of stone, cut from trachytic rock that occurs a few 

 miles south of the works. The shaft is of common brick with a lining of fire- 

 brick from the hearth up to the throat. 



In the drawings, E is the hearth, or sole ; F, the sump, or receiver, into 

 which the metal runs on being tapped from the furnace ; t, tuyeres ; g, blast- 

 pipes ; h, pipes to supply water to the tuyeres ; L, lining of the furnace ; M, 

 throat; N, floor for feeding ore; S, stack. 



The capacity of one of these furnaces is from 12 to 13 tons per day of 

 twenty-four hours. The ore being broken into small pieces is spread upon the 

 charging floor and mixed with flux. This sometimes consists of limestone, 

 but generally of slag, or both together. Litharge, the product of the cupelling 

 furnace, is also sometimes used with fresh ore. The ore for the charge, being 

 mixed with about 25 per cent, of flux, is supplied to the furnace with a sufficient 

 quantity of charcoal, that averages about 15 bushels to the ton of ore. About 

 100 pounds of the mixed charge and coal is fed to the furnace at once, the sup- 

 ply being continuously kept up as the operation of smelting proceeds. The 

 blast is supplied by a fan-blower which is driven by the steam-engine for- 

 merly provided for operating the stamping and grinding machinery in the old 

 mill. 



When the furnace is in regular operation the slag is discharged contin- 

 uously, while the metal is tapped off, at intervals of an hour or two, into an iron 

 receiver, whence it is dipped out and cast in pigs or ingots of convenient size 

 for further handling. 



The yield of metal, consisting of lead, antimony, and silver, is from 45 to 

 50 per cent, of the ore smelted ; one furnace smelting 12 tons of ore in a day, 

 supplying consequently about 5 tons of crude metal. The ore, originally con- 

 taining $80 per ton in silver, yields metal which contains from $150 to $200 

 per ton. The slags are constantly examined. Usually they are quite poor, 

 but if found to contain an available percentage of metal are broken up and 

 returned to the furnace with a fresh charge of ore. 



The consumption of charcoal in this smelting process is usually about 15 



