Hot Blast in the Smelting of Lead. 



171 



thick, leaves the inside space about four and a half inches by 

 twelve and a half The blast passes into this chest by a pipe at 

 E and out at F, whence by a curved pipe it is discharged into the 

 iire through a ' twyer' cast in the air-chest at G, two inches above 

 the level of the lead reservoir. 



Fig. 2. 



The lead reservoir A (fig. 2,) is filled with metallic lead, which 

 in the process of smelting continues in a state of fusion, and while 

 the furnace is used is not withdrawn. The 'charge' in the pro- 

 cess of smelting, floats upon the melted lead, and the metal as 

 smelted falls into it, flows over and discharges through the groove 

 in the hearth. In working the furnace, the smelter throws im- 

 mediately in front of the blast, two or three billets of light wood, 

 say two inches in diameter and sixteen inches long, upon which 

 are thrown up the ' charge' in process, and fresh galena, filling 

 the furnace near even with the top of the air-chest and sloping 

 down to the hearth. The blast being let on, strikes upon the 

 billets of wood and is thus diffused evenly through the whole 

 charge, carrying with it the flame of the fuel. 



It will be perceived that the air passing into the hollow chest, 

 acts as a refrigerator upon the inner walls, and thereby prevents 

 their being heated so high as to combine with the sulphur, by 

 which they would soon be destroyed ; and also by preventing an 

 accumulation of heat in the walls, keeps the furnace of a uniform 

 temperature, which if not thus moderated would soon run so high 

 as to fuse the galena and thus check the smelting. 



