GOLD MINING IN COLOEADO. 



581 



furnace are six small doors through which the charge is introduced and stirred 

 while in the furnace. The charge being put in at the end most remote from 

 the fireplace, is gradually heated on the highest hearth, and, as the charges 

 preceding it are advanced, it is moved on to the next hearth, making room for 

 a new one, and so on, until on the third or lowest hearth, next the bridge, it 

 is subjected to the highest heat. Each charge consists of one ton to a ton 

 and a half of material, and three charges are put in during twenty-four hours, 

 each charge remaining on each hearth nearly three hours. While in the 

 furnace the charge is constantly stirred. Two men are required on each 

 shift for each furnace; and one cord of wood is consumed in twenty-four hours. 

 The capacity of each furnace is from three and one-half to four tons per day. 

 The costs of treatment are said to be $5 per ton.^ 



The hand-broken ore, after being roasted or calcined, is prepared for the 

 smelting furnace by crushing. This is done by Cornish rollers, of which 

 there is a single pair; the rollers are 26 inches in diameter. In the crushing- 

 house is also a Dodge crusher, for preliminary crushing of the larger pieces, 

 chiefly used for breaking up matt that is of too low grade for shipment, and 

 which, consequently, has to be subjected to a second smelting. After passing 

 through the rollers, the crushed product falls upon a No. 4 screen, that which 

 is fine enough to go through being carried to the smelting furnace, while the 

 coarser portion is returned to the rollers. 



The material, ores and tailings, having been calcined and crushed to the 

 desired fineness, is then ready for the smelting furnace. This is a reverbera- 

 tory, and resembles the melting furnace generally used in England for copper 

 smelting. The foundation of the furnace is of solid stone, with a vaulted space 

 under the hearth. The latter is 14 feet long by 9^ wide, inside; oval in shape 

 or horizontal section, the smaller end being near the stack. The fire grate, 

 at the opposite end, is 5 feet by 4, separated from the hearth by a bridge, 18 

 inches high. The arch is 18 inches high above the bridge, and slopes toward 

 the opposite end, its mean height above the hearth being about two feet. 



^ In addition to tlie calcining furnaces just described, there are two Gerstenhofer 

 furnaces, designed for tlie same purpose. These furnaces, however, have not yet been 

 operated satisfactorily, owing, it is said, to the poor quality of the flre-brick employed 

 in their construction. 



