REFINING OF LEAD* 2 1 L' 



tfieir bafe for the evaporation of the moifture, and to difpofe 

 gt' them fo as moft effedlually to anfwer this purpofe. Thefe 

 channels or vents are to be covered with a bed of fcoria, upon 

 which a pavement is to be made of the moft porous bricks, and 

 of the thicknels of a fingle brick. 



On this area or pavement, which ought to be concave like The cupel Is 

 the bafe upon which the afties of the ordinary cupels are ^j^j^ ^ U^Jl" ^.1 

 placed, mud be laid a quantity of founder's fand, a little moift- inftead of bone 

 ened. If it be not adhefive enough, a little clay may be "* 

 added, in order tc give the requifite folidity, and the whole 

 carefully mixed. 1 he fand mufl: be rammed down in the fame 

 manner as is done to confolidate the afties in the ufual way, 

 and abafon for refining mufl be formed, equally rammed in all 

 its parts. The thicknefs of this cupel (hould be about fix: 

 inches; and it may be made in two layers, as we fhall here- 

 after obferve* 



After the bafon has been in all parts uniformly beaten or 

 rammed down, it will be proper to fift over the whole furface 

 two or three quarts of wood afhes, which may be made to 

 adhere by ramming. 



When the cupel is thus prepared, the head of the furnace It may be dried 

 muft be lowered, and a moderate fire kept up for feveral hours, ^^^°" "^^> 

 in order to evaporate part of the water from the fand. The 

 reft will be driven out, without inconvenience, through the 

 vents during the refining. 



After a fufficient drying, which may even be difpenfed — but this Is not 

 with; the head is to be raifed, the cupel, fufl?ered to cool a ^^^^^^^"^^'^ "^- 

 little, and ftraw or hay then laid upon it, and upon this the Method of 

 pigs or pieces of lead, which are to be gently put down, in j^^^''g'"S ^^^ 

 order that their weight may not make irapreflions in the fand. 

 The ftraw is ufed for this purpofe, in our method as well as the 

 common method; and it would be convenient that the lead 

 fliould be caft in iron hemifpherical moulds or pots inftead of 

 the prifmatic form, as thefe pieces would" be lefs fubjed to 

 damage the cupel. 



When the quantity of lead neceflary to fill the cupel is ar- 

 ranged in the furnace, the head is to be lowered and luted a!l 

 round with clay, after which the fire is to be applied as in the 

 ufual procefles. 



When the^ lead is in per fed fufion, and the bath covered Fufion. 

 with drofs and coally matter from the ftraw, this Ikum muft be^j.^^^^^"^ "^ '^* 

 P 2 raked 



I 



