Mr. H. L. Pattinson on the Smelting of Lead Ore, 8$c. 161 



disposition to become very soft. Fifth. — Coal should be also supplied 

 judiciously ; too much unnecessarily increasing the bulk of the brouse, 

 and causing the hearth to get too full. 



When the ore is of a description to smelt readily, and the hearth is 

 well managed in every particular, it works with but a small quantity of 

 brouse, which feels dry when stirred, and is easily kept open and per- 

 meable to the blast. The reduction proceeds rapidly with a moderate 

 degree of heat, and the slags produced are inconsiderable; but, if in 

 this state, the stirring of the brouse and exposure upon the workstone 

 are discontinued, or practised at longer intervals, the hearth quickly 

 gets too hot, and immediately begins to agglutinate together ; render- 

 ing evident the necessity of these operations, to the successful manage- 

 ment of the process. It is not difficult to understand why these effects 

 take place, when it is considered, that in smelting by means of the ore 

 hearth, it is the oxygen of the blast and the atmosphere which princi- 

 pally accomplishes the reduction ; and the point to be chiefly attended 

 to, consists in exposing the ore to its action, at the proper temperature, 

 and under the most favourable circumstances. The importance of hav- 

 ing the ore free from impurities, is also evident ; for all the stony or 

 earthy matter it contains impedes the smelting process, and increases 

 the quantity of slags. A very slight difference of composition of per- 

 fectly dressed ore may readily be understood to affect its reducibility ; 

 and hence it is, that ore from different veins, or the same vein in dif- 

 ferent strata, as before observed, is frequently found to work very dif- 

 ferently when smelted singly in the hearth. It happens, therefore, that 

 with the best workmen, some varieties of ore require more coal and lime, 

 and a greater degree of heat, than others ; and it is for this reason that 

 the forestone c, Figs. 1 and 3, is made moveable, so as either to answer 

 for ore which works with a large or a small quantity of brouse. 



It has been stated that the duration of a smelting shift is from 12 

 to 15 hours, at the end of which time, with every precaution, the hearth 

 is apt to become too hot, and it is necessary to stop for some time, in 

 order that it may cool. At mills where the smelting shift is 12 hours, 



