ZINC 



1191 



iron doors, by which the too rapid cooling of the pipe a, I, c, is prevented. The fuel 

 employed is coal, which is burnt on the grate o, situated in the centre of the furnace. 

 The retorts are charged with a mixture of calamine and small coal, or more frequently 

 coke-dust, since, when coal is employed, the products of distillation are found to be 

 liable to choke the pipe a, b, c. 



The zinc escapes by the opening c, of the adapter, and is received into the cavities 

 o, of the furnace. 



The furnace shown in figs. 2157, 2158, 2159, is for remelting the metallic ziuc. 



Fig. 2157, is a front view ; Jig. 2158, is a trans- 

 verse section ; Jig. 2159, a view from above : a, is 

 the fire-door ; b, the grate ; c, the fire-bridge ; d, 

 the flue ; e, the chimney ; f, f, f, cast-iron melting- 

 pots, which contain each about 10 cwts. of metal. 

 The heat is moderated by the successive addition 

 of pieces of cold zinc. The inside of the pots 

 is sometimes coated with loam, to prevent the iron 

 being attacked by the zinc. 

 In some establishments, and particularly those 



2157 



2160 



2159 



at Stolberg in Prussia, the retorts have the form represented by D, fig. 2160, c'is an 

 adapter also of fire-clay ; B a cone of wrought iron, and A a small vessel of the same 

 material for the collection of the oxide, and furnished in the bottom with an aperture 

 for the escape of the gases generated. 



These are arranged on either side of a grate as represented, fig. 2161 ; an internal 

 opening serving for two retorts, and of which there are usually twelve in each 

 furnace. E is the fire-door ; F grate ; G chamber in masonry of furnace ; H dia- 

 phragm of fire-brick supporting adapter, in the depressed part of which the metallic 

 zinc is collected and subsequently removed by a scraper, as in the case of the 

 cone of the Belgian retort. The wrought-iron vessel A, is supported by a chain or 

 wire j. 



Fig. 2162 represents a longitudinal elevation of the roasting furnace employed. 



2162 



-24- 



Old English Process. The English furnaces formerly used for smelting zinc ores 

 were sometimes quadrangular, sometimes round ; the latter form being preferable. 



