374 On Smelting of Lead, 



fractory slags to keep it of a moderate size. With too large 

 a protuberance, the hearth works most at front ; with too 

 small, chiefly at the back. 



In general a noze may be prevented growing too large, 

 by laying the fuel principally near the pipe-stone, and oc- 

 casionally forcing in a pricker through the tuyre. 



A noze may be enlarged by a contrary situation of the 

 fuel, and throwing in close to the pipe-stone a few shovels 

 of dust and ashes from the top of the hearth. 



The fuel used at the slag hearth is coke. 



The scoria, the refuse of the operation in the slag hearth, 

 is called black slag; it contains a portion of metallic lead 

 which is separated by stamping and washing. 



The lead obtained by the slag hearth is hard and sonorous; 

 it is of an inferior quality, and unfit for many of the pur- 

 poses to which common lead is applied. 



Cupola Smelting. 



The method of smelting lead by the cupola furnace as 

 principally practised in Derbyshire, I have taken from Wat- 

 son's Chemical Essays; a more corrector interesting ac- 

 count cannot be given. 



'' The furnace called a cupol, or cupola, in which ores 

 are smelted by the flame of pit coal, is said to have been 

 invented about the year 1698, by a physician named Wright; 

 though Beecher may, perhaps, be thought to have a prior 

 claim to it? invention, or introduction into Germany. But 

 vt'hoever was the inventor of the cupola, it is now in general 

 use, not o'.ily in Derbyshire and other countries, for the 

 smelting of the ores of lead, but both at home and abroad, 

 where it is called the English furnace for smelting copper 

 ores. This furnace is so contrived, that the ore is melted 

 not by coming into immediate contact with the fuel, but 

 by the reverberation of the flame upon it. The bottom of 

 the furnace upon which the lead ore is placed is somewhat 

 concave, shelving from the sides towards the middle ; its 

 roof is low and arched, resembling the roof o^ a baker's 

 oven ; the fire is placed at one end of the furnace, upon an 

 iron grate, to the bottom of which the air has free access; 

 at the other'end, ppposite tp the fire-place, is a high perpen- 

 dicular chimney ; the direction of the flame, when all the 

 apparatus in the sides of the furnace are closed up, is neces- 

 sarily determined bv (he stream of air, which enters at the 

 grate, towards the chimney, and in tending thither it strikes ^ 

 upon the roof of the furnace, and being reverberated. from 

 thence upon the ore, it soon melts it. 



"It 



