84 Zinc Desilverization. 



The coke either comes from Coimellsville or is Illinois gus- 

 coke. The Connellsville coke weighs 40 Ihs. to the bushel. It 

 costs at Cheltenham 110.00 per ton, and the gas-coke costs 

 7 cents per bushel of 40 lbs. The lead contains about \ per cent, 

 of arsenic and antimony. When it is yery impure, it is polled 

 directly after it is drawn from the tap-liole. Ordinarily it is 

 cast into pigs. The furnace is tapped into a bra?eined basin, 

 and the lead cast from there : three to four tappings are made 

 in 24 hours. 



The copper is concentrated in an iron matte, which contains 

 a little silver and gold. It forms about 5 per cent, of tiie total 

 product of the works, and is worked at the end of a campaign, 

 when it is treated with pyrites and concentrated to 50 per cent, 

 of copjDer. Sometimes a little speisse is formed, when the ore 

 contains considerable arsenic. 



The slag varies between a singulo and a bi-silicate. The slag- 

 pot is hung directly under the axle of the buggy, and holds from 

 650 to 700 lbs. The slag-buggy, Fig. 2, is so arranged that the 

 line of its axis runs through the center uf the pot near its top. 

 The pot is caught by three hooks, which prevent it from tipping. 

 It is always white-washed before it is used. When full, it is al- 

 lowed to remain until the outside chills for about half an inch, 

 and is then caught by the buggy and dumped. To prevent the 

 pot from falling off when dumjjed, a projection is placed on the 

 front of the pot, which is caught in the hook on the curved part 

 of the axle. Fifteen tons of slag are joroduced in the treatment 

 of 10 tons of ore. Of this amount, 30 per cent, is poor and is 

 thrown away ; the rest is re-treated. 



The number of workmen required for a twelve-hour shift is, 

 below, one founder and two helpars, who wheel away the slag, 

 and above, one charger and one helper. 



A campaign with water-backs lasts as long as a su|)ply of ore 

 can be had. If the supply was constant, it would probably be 

 about six weeks. With a sandstone lining, it lasts about the 

 same time ; but repairs to the furnace are much more expensive. 

 With a brick lining, it lasts only three weeks. In blowing out, 

 slag is used exclusively, to clean the furnace as much as possible. 



The amount of ore treated at Cheltenham is from 500 to 600 

 tons per month. From 5 to 6 tons per day of lead, containing 



