

OF ARKANSAS. 



157 



Where fuel is cheap, the calcination is advantageously performed in heaps. 

 The heaps are formed by alternate layers of wood and carbonate of zinc; 

 fire is set to the lowest layer of wood, and the ore left to the influence of 

 heat and air; by this means the water is removed, but not the carbonic 

 acid, and the state of cohesion lessened. 



In the English process, the calcined ore is mixed with about one-seventh 

 of its weight of coal, and filled into large crucibles or pots. These pots 

 are made of fire-clay, and cement of old pounds finely ground; they are 

 covered with a lid, through an orifice of which the charge is introduced, 

 and are provided, at the bottom, with an aperture; to this aperture a long 

 sheet iron pipe is joined, which dips, at its end, into a vessel filled with 

 water. On heat being applied, the oxide of zinc becomes reduced, the 

 metal is vaporized, passes through the iron pipe, and collects in drops in 

 the water vessel. From 6 to 8 pots are placed in a furnace; a furnace 

 will work up from G to 10 tons of ore in 14 days, consuming from 22 to 24 

 tons of coal, and yielding 2 tons of zinc, on an average. A pot lasts 

 about four months. 



In the Belgian process, the reduction furnace is filled with long, hori- 

 zontal earthen tubes, from 3 to 4 feet long, and from 4 to 5 inches in 

 diameter; 22 tubes in each furnace; the tubes are filled with a mixture of 

 ground ore and coal, (1 volume of ore to i to f volumes of coke or char- 

 coal, broken to pieces the size of nuts); to each tube a conical piece of 

 cast-iron is attached, in a slightly slanting position; these conical pipes 

 serve as receivers and condensers of the vaporized zinc, and are raked 

 out every two hours. Each earthen tube holds 40 lbs of the mixture of 

 ore and coal; the distillation is completed in 12 hours, and each furnace 

 yields every 12 hours, 100 lbs. of crude zinc; on being remelted and cast 

 into moulds, the crude zinc loses 10 per cent. For every pound of zinc 

 about 28 lbs. of coal are used. 



In the Silesian process, the small earthen tubes are replaced by muffles 

 made of fire-clay mixed with ground potsherds; the muffles are from 3 to 

 4 feet long, and have a diameter of from 14 to 18 inches. The number of 

 muffles in a furnace varies from 5 to 10; in Upper Silesia, double furnaces, 

 holding 20 muffles, are in use. The charge consists of calcined ore mixed 

 with an equal volume (about one-fifth by weight) of cinders. A single 

 muffle will produce from 40 to 50 lbs. of zinc daily. A muffle will last 

 several months. 



The crude zinc obtained by any of the above described processes has to 

 be remelted; in this operation the heat must not rise above a low red-heat, 

 and the surface covered with a layer of charcoal. Experience has shown 

 that, with careful management, 100 lbs. of crude zinc will yield from 92 



