Mr. H. L. Pattinson on Smelting Lead Ore, &;c. 153 



ore itself may be cubical, steel-grained, or antimoniated, or a mixture of 

 two or the whole of these in various proportions ; and, besides hetero- 

 geneous impurities, it frequently contains a greater or less proportion of 

 iron, as an ingredient in its composition ; these circumstances render 

 its quality so various, that, when laid down at the smelting-house, it is 

 very difficult to pronounce two parcels from different veins, or from the 

 same vein in different strata, exactly alike. It consequently happens 

 that one variety of ore is sometimes found, without any very obvious 

 cause, to be much more refractory in the fire and less easily reducible 

 than another, and among a number of parcels this difference is occa- 

 sionally very considerable. 



At nearly all the smelting-houses in this district, the practice prevails 

 of smelting the ore from each vein, where the quantity is considerable, 

 by itself, although most smelters admit that a mixture of different kinds 

 of ore has frequently a very beneficial effect in promoting the reduc- 

 tion of each. In smelting ore from the same vein, it is the practice to 

 treat the different portions, into which it is divided in the washing pro- 

 cess, separate from each other; that is, the portions called, technically, 

 seive ore and smiddam, are smelted separate from the slime ore, lest 

 the latter, which is in very small particles, should be driven away by 

 the draught and blast, by which the former is roasted and reduced into 

 Lead. 



The process of smelting may be most conveniently described under 

 four heads, viz. : — 



Roasting of the Ore. 



Smelting in the Ore Hearth. 



Smelling in the Slag Hearth. 



Smelting of Hearth Ends and Smelters' Fume. 



ROASTING OF THE ORE. 



The process of roasting is nothing more than heating the ore to a 

 proper temperature in a reverberatory furnace, during which it under- 

 goes a change, by the partial expulsion or acidification of the sulphur it 

 contains, which renders it afterwards more easily reducible. 



