2li Memoir on ihe Rcjinmg of Lead; 



oxide contained in the aflies, which oppufe fufion, and the 

 Icoriae of which always carry with them fonie of the metal. 



In a cupcll of aflits beat into an' oval circle of iron, the 

 greater diameter of which is only five or fix feet and the 

 lefs one vard, the Englifli refine from a. ton to 23 cwt. of 

 lead, which is converted into beautiful litharge, except the 

 fmall portion which penetrates into the cupell, the thicknefs 

 of which is only about 2} inches, and which is fupported 

 under the arch of the furnace by two bars of iron. A pair 

 of leather bellows drive the litharge towards the anterior part 

 of the furnace, from which it falls, without interruption, on 

 the floor of the foundry, while, to fill up the vacuity left by 

 the oxide running off, an ingot of lead placed clofe to the 

 bafe of the bellows is made to advance gradually into the in* 

 terior part of the furnace. This lead, by fufing, keeps the 

 cupell fuUtill towards the end of the operation. 



If I have here given a ftiort view of the procefs of the 

 Englifh, it is only to fhow that it is poffible to perform ope-^ 

 rations of refining by employing only a fmall quantity ot 

 aflies for the conftruftion of cupells. Thofe in queftion do' 

 rot abforb 90 pounds of oxide in the large quantity of lead 

 which is refined. 



It is then proved that metalkirgvfts have always endea- 

 voured to obtain the greatefl. quantity poffible of litharge, 

 and little aihes impregnated with oxide ; but as they thought 

 that they ought not to deviate from the dociuiaftic procefs, 

 they have always conftruded their cupells of aflies. 



It has been feen that in cupellation on a fmall fcale, lead, 

 in proportion to its oxidation, penetrates the aflies. When no 

 more -is left, the fmall button of filver remains pure at the 

 bottom of the bafon under a fpherical form. This operation 

 takes place with the more celerity, as the furface of the mafs 

 is aKvays convex in thefelinall vefiTcls; which allows the oxide 

 to flow as on an inclined plane, towards the edges of the 

 fupcll, where it is immediately imbibed. 



The cafe is not the fame with cupelts on a large fcale, 

 which are feveral yards in diameter: bellows muft be ap- 

 |)lied, the wind of which ferves not only for accelerating the 

 oxidation, but aU'o for driving the litharge towards the gutter 

 formed for its c.cape. 



\\'e have remarked the inconveniences and even the im- 

 poffibilitv of making the whole lead penetrate into the afties 

 of large cupells : oxidation, indeed, is not eftet^ed but in the 

 parts of the mafs expofcd to the contaft of the air or to the 

 wind of the'bellows; but as litharge, towards the middle of 

 the bdfon, could not reach its edges, it would remain there 



in. 



