164 Mr. H. L. Pattinson on the Smelting of Lead Ore, fyc. 



whole of the upper part of the hearth is filled with peat and coal, which 

 is continually supplied, with the addition of coke as the fire gets hotter, 

 until an intense heat is produced, and a body of fuel obtained, filling 

 the uppper part of the hearth. Some of the grey slags from the smelt- 

 ing hearth, unbroken, as picked out of the brouse, are now thrown upon 

 the top, or rather round the edges of the fire, which fuses them rapidly 

 into a liquid glass, and any lead they contain is set at liberty ; the blast 

 at the same time tending to reduce any particles of ore which may have 

 escaped the action of the ore hearth. The lead and the melted glass 

 both sink down through the porous mass of cinders placed in the lower 

 part of the hearth ; the lead descending more rapidly, both on account 

 of its greater tenuity and superior specific gravity, very soon collects be- 

 low the cinders, in the metal pan placed to receive it, and filtering through 

 under the division, b, is obtained without much impurity in the part c, 

 Plate II. Fig. % out of which it is cast into pigs. The thick fluid glass, 

 called black slag, after reaching the cast-iron bottom of the furnace, 

 having cooled and thickened a little, does not sink further, but is made 

 to issue through a small taphole, and flow over the cinders placed in the 

 pan, running into the pit filled with water in a continued stream. By 

 falling while hot into cold water, the black slag is granulated, and, as 

 small particles of lead may be carried over with it, through inattention 

 on the part of the workman, or otherwise, the granulated slags are 

 carefully washed at most smelting mills before being thrown away. 

 According to Dr. Thompson (A?m. Phil. vol. iv.) these slags consist of 

 silex, lime, and oxide of iron, with some alumine, oxide of antimony, 

 and oxide of lead. Their composition must, however, be various, de- 

 pending upon the nature of the ore from which they are produced ; in 

 all cases they are formed from the earthy matter contained in the ore 

 and coal, which the metallic oxides convert into a glass. 



In working a slag hearth, the workman's attention is principally re- 

 quired to supply grey slag and fuel as it is melted down and consumed, 

 to keep the nozzle of the bellows clear, and to guard against the me- 

 tallic lead running along with the slag, into the pit of water. 



Two men are generally employed to work a slag hearth, but, at some 



