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GEOLOGICAL RECONNOISSANCE 



The smelting of zinc from these ores, although not quite as simple a 

 process as the smelting of lead from galena, offers no difficulties: the ore, 

 reduced to a proper size, is simply mixed with a sufficient quantity of coal, 

 and heated, in a closed vessel, to a temperature high enough to cause the 

 reduction of the oxide; the metal, being volatile, distills over and is col- 

 lected in a receiver. The execution of the process varies somewhat in 

 practice; at present, three methods are principally in use, known as the 

 English, the Belgian, and the Silesian method, each possessed of its pecu- 

 liar advantages and disadvantages. 



The only preliminary operation which the ores are subjected to, besides 

 the necessary sorting and bruising, is the calcination, (and even this opera- 

 tion is sometimes omitted in England). The calcination is generally per- 

 formed in reverberator)' furnaces, and has the object of removing carbonic 

 acid and water, and lessening the cohesion of the ore; it is a necessary 

 operation if the carbonate of zinc contains blende, to convert the latter 

 into oxide of zinc; in this case, a small proportion of coal must be added. 



