[ 210 ] 



XXXTI. Memoir on the Hrfining of Letid ; lu'ith fome Rcjltc- 

 tions on the bicowjenuiiie of Ajh Cupel Is ; and the De/crtp~ 

 tion of a new grid econovilcal Method oj coiijiftut'ing Ciipeils 

 or Rejimng Veljels : read in the French JSiiiionat Injliiute. 

 i^' C. DuH AMEL, Member of the Injliiute and Infpe&or 

 of Mines *. 



At is well known, that to feparate lilver from lead, a metal- 

 ■lurs;ic procefs called refining or cupellation, performed in a 

 Yefll'l called a cupell, has been employed : it is known alfo 

 that this veflel is compofed cither of the aflies of the bones 

 't)f animals, or of thofe of vegetables, after they have been 

 lixiviated, to free them from the faline matters which they 

 inay contain. 



The great quantity of wood-aflies which muft be employed 

 in the conllriicliion of cupells, and the difficulty of obtaining 

 them, long ago induced me to endeavour to difcover a Am- 

 pler and lets expenfive method of conftruAing the vefl'els in 

 queftion. The old chemilts having obferved that lead be- 

 comes oxidated, or reduced into what is called litharge, -when 

 expofed to heat, or the contaA of the atmofpheric air, while 

 the filver united to it retains its metallic form, nothing feemed 

 neceflary but to find the means of feparating thcfe two me- 

 tals. They were condufted to the method of accomplifliing 

 this bv obferving that the oxide of lead, in its flate of liquefac- 

 tion, eafilv penetrates the fubftances which are in conta£l with 

 it, and efpecialiv bone-aflies, without deforming the veilels 

 which are formed of them. No matter, indeed, is more 

 proper than the latter for conftruAing fmall refining cupells. 



The difficulty, and often even the impoffibility, of obtain- 

 ing about 160 Englini gallons of aflies for each operation of 

 refining on a large fcale in the German furnaces, made the 

 proprietors have recourfe to wood-afhes; but, befides that 

 thefe aflies are expenfive, it often happens that they cannot 

 be procured in futlicient quantity. They are even attended 

 with one inconvenience, which is, that they come off, and 

 float on the fufed lead ; the refining then fails : and this 

 takes place every time that the aflies are badly prepared, that 

 the cupell is infufficiently or not uniformly beat, or when 

 the canals dcfiincd for. the evaporation of the moillure are 

 neither in futiicient number, nor properly arranged, nor co- 

 vered with a ftratum of fcoricc, on which is efiabliilied the 

 bottom, thatreceives the aflies, and which ought to be eon- 



• From the "Journal dts Afiae;,. No. 64. 



ftrudled 



