On Smeli 'rg of Lead. 373 



the space left between the bottom of the hearth and the 

 lower front bearer is called the breast; — (/) is the sump or 

 pot to contain the lead, as it flows from the hearth ; the 

 space between the breast and the sump is paved with old 

 castings imbedded in dust, and the joints filled with thin 

 mortar grout; near the sump is a mould for casting the lead 

 into pi<is. 



The hearth is prepared for working, by sliqhtlv ramming 

 into the bottom a quantity of coal ashes; the sump is also 

 filled, and the space between it and the breast ; the dotted 

 part ig g if) fiil'. 3, rcpresenls the coal ashes: the fire is 

 next lighted, and when the interior of the hearth has ac- 

 quired a good red heat, ihe smelter throws on a few shovels 

 full of gray slaas (which have been previously broken to the 

 size of aneog), and as tlie hearth settles, occasionally adds 

 fuel or more slags as may be required : in a few minutes 

 after charsino: wiih the slags a small perforation is made in 

 the breast by passing a pointed iron rod through the ashes 

 close to the bearer; the liquid scoria and lead flow through 

 this opening down the inclined plane formed by the ashes ; 

 as they become hot the lead filters through them, and finds 

 its way into the sump; the scoria from its viscidity remain- 

 ing on the surface, from whence it is removed occasionally 

 as it cools and becomes hard. 



The slag hearth is continued working for 12 or 14 hours, 

 the smelter adding materials occasionally as required, and 

 judging of the proportion of fuel by the heat and appearance 

 of the fluid scoria. 



At the conclusion of the day's work the hearth is suffered 

 to burn down as low as possible; and when the scoria ceases 

 to flow the bellows are stopped, the scoria on the bed of 

 ashes removed, and the lead which has collected in the 

 sump is cast into pigs. Cool ashes are next spread over the 

 hot bed, and the hearth drawn and cleared from what re- 

 mains in it, and when moderately cooled, prepared with a 

 bottom of ashes for a succeeding day's work. 



Tlie principal art in working a slag hearth is to keep a 

 proper noze, and to have the hearth light and open in front, 

 otherwise the blast does not work well and diffuse itself 

 equally through all parts, but forges itself up behind 3^nd 

 very soon destroys the pipe-stone. 



The noze is a ])r(»tuberauce which surrounds the orifice, 

 through which the blast passes ; it is formed l)y the vitrified 

 slags iritkhiig down the pipe-stone, and cooh-d by the blast 

 as It enters the hearth. With very fusible slags it is some- 

 times dillicult to get 4 proper noze to form, and with re- 

 A a 3 fractory 



