COLLECTIONS IN ECONOMIC GEOLOGY AND METALLURGY. 



59 



TREATMENT OF THE ORE. 



Formerly the lead was extracted iu Flintshire and Scotch hearths, 

 small reverberatory furnaces, which treat from 1 to 2 tons of galena, 

 and produce lead at a single operation. They had the advantage 

 of being inexpensive and suited to small mines; even farmers fre- 

 quently owned them and worked them at odd intervals. They were, 

 however, very crude and wasteful, as is well illustrated by the follow- 

 ing analysis of the slag produced : 



Flintshire '^Grci/ Slaij" Besloge. 



Per cent. 



Silica (SiOj) 8.3 



Protoxide of iron (FeO) 10.2 



Lime(CaO) 16.0 



Magnesia (MgO) 4.0 



Snlplinr (S) 4.5 



Lead(Pb) 32.5 



At present the metallurgical operations are much more complex, and 

 are carried out on a much larger scale. The galena is first roasted in 

 large Frieberg hearths, which are low reverberatory furnaces 66feetlong 

 and 12 feet wide, to oxidize the sulphur. The galena, in 500-pound lots, 

 is charged into the end nearest to the stack, and as the sulphur oxidizes 

 it is moved along towards the hearth. When it reaches the hearth the 

 sulphur should be reduced to from 4 to 6 per cent., and as soon as this 

 condition is attained sand is thrown upon it in order to sinter the mass, 

 so that it can be withdrawn and readily handled. The following analy- 

 ses represent the roasted mineral : 



Boasted mineral. 



The roasting of the sulphides is a more rapid and easier process than 

 roasting the galena on account of the iron they contain. They are 

 thrown in one-half to one-third the wa^^ down the furnace, and when 

 the roasting is complete are withdrawn without sintering. The follow- 

 ing analyses represent the roasted sulphides : 



