104 Zinc Desilverization. 



Cast iron box, - - - - - - 1,260 lbs. 



Grate-bar bearers, . - - - - - 306 



Two standards, - - . ' . . . 530 



Cast iron, 2,096 



Wrought iron bars, 181 



The iron-work costs from $150 to $165. 



The furnace is fired until the retort gradually arrives at a 

 dull red heat, when a charge of 250 to 400 lbs. of the alloy, 

 broken up while still soft, in order to get it of a suitable size for 

 the charge, and mixed with five to six lbs. of small charcoal, i^ 

 introduced with a scoop. It is brought to the retorts at Mans- 

 field in a box on wheels, about three by three feet, and a little 

 lower than the mouth of the retort. As soon as the retort is 

 charged, the temperature is gradually raised to a white heat, 

 and when the zinc vapors begin to appear, the condenser, made 

 in the same way as that at Cheltenham, is put on. At Mansfield, 

 they use for a condenser a retort, Ko. 100, with the bottom 

 broken out, and a hole punched in the side to discliarge the 

 zinc. A piece of common stove-pipe is attached to the mouth 

 to carry off the flames. 



The retorts usually last fourteen to fifteen charges, but some 

 have been made which lasted forty-five. As soon as the zinc 

 commences to collect, a wagon, containiiig the moulds for the 

 zinc and the support for the condensers, is rolled up against the 

 front of the furnace, which has been entirely free since the 

 charge was introduced. The zinc distils, and is collected in the 

 condenser, and held there by the oxides and blue powder which 

 collect in front, and are used by the Avorkmen to form a dam to 

 hold the zinc back. When sufficient has collected it is draAvn 

 into the moulds. The total amount collected as metal varies 

 from 45 to 55 per cent., and is used over again. The blue pow- 

 der and oxides amount to from 20 to 30 per cent.; these are sold 

 to the ziuc works. Some of the zinc is lost by volatilization, 

 and from 0. 7 to 1 per cent, retained in the lead. 



As soon as the amount of zinc escaping appears in small 

 quantity, the lead contains but little zinc ; but as it is desirable 

 to remove, as far as possible, the last traces of it, the heat is kept 

 up, the condenser is removed, and small pieces of wood are put 



