Lead. 
191 
ore lead. After the lead has all flowed out of the furnace, 
they stop up the tap-hole, and drawing down the slag and 
lime into the middle of the furnace, they raise the fire till 
the mixture of slag and lime, which they simply term slag, 
is rendered very liquid ; upon this liquid mass, they 
throw another quantity of lime to dry it up, as in the for 
mer part of the process. This second mixture of slag 
and lime is then raked out of the furnace, and the small 
portion of lead separated from the fusion of the first, gene- 
rally to the amount of twenty or thirty pounds, being let 
out of the furnace, a new charge of ore is put in, and the 
operation re-commenced. In order to spare the lime, and 
the expence of fuel attending the fluxing of the mixture 
of lime and slag, they have in some furnaces lately com 
trived a hole, through which they suffer the main part of 
the liquid slag to flow out, before they tap the furnace for 
the lead ; upon the little remaining slag they throw a small 
portion of lime, and draw the mixture out of the furnace 
without smelting it. This kind of furnace they have nick- 
named a Maccaronh 
The process of smelting here described, appears to be 
defective in some points, which I will take the liberty to 
mention, and at the same time suggest the means of im- 
provement ; without, however, presuming to say, how 
far it may be expedient to adopt the proposed alterations ; 
being sensible that what may appear very feasible in 
theory, or may even answer in small assays, may not be 
practicable in large works. 
The first alteration which I would propose to the con- 
sideration of the lead smelters, is to substitute an horizon- 
tal chimney of two or three hundred yards in length, in 
the place of the perpendicular one now in use. In the 
preceding Essay, which was first published in 1778, men- 
tion is made of the probability of saving a large quantity 
of sublimed lead, by making the smoke which rises from 
