214 Memoir on the Refining <if Lead; 



furfaee of the mafs. This iron, beino; lighter than lead, floats 

 over it and ahl'orbs the arfenic, after which the mafs niufl 

 be fcummed : foon after, the litharge is formed' without any 

 obltacle. This method is employed in Saxony. 



The neeeflily of adding fand to the afhes of cnpells muft 

 have condii(Sled to the difcovery of the following means, which 

 I fhall here propofe. 



Neil) jyhfhod of conJiruSli?ig Bafons for Rcfinmg. 



Without making any change in the mafon-work of the 

 refining furnace, called the German, care only mnft be taken 

 to form at the bottom a fufficient nmiiber of canals'for the 

 evaporaiioa of the moifturtr, and to arrange them in the 

 manner belt calculated to pruduce that effetl. Thefe canals 

 or fpiracles mud be covered with a bed of fcoriae, over which 

 a pavement is to be made of one layer of the moft porous 

 bricks. 



On this area, which muft be concave like the fole on which 

 the aflies of common cupells are beat, place founders' fand 

 a little moiftened ; to which may be added a fifteenth part 

 of argil, it it is not fufficiently cartliv, in order to give it thq 

 requifite folldity ; and the whole muO: be carefully mixed. 

 This fand mull be rammed in the fame manner as for con- 

 folidating aflies ; and a refining bafon is to be formed in like 

 manner, uniformly beat in all its parts. The thicknefs of 

 this cupell muff be fix or feven inches : it may be formed of 

 two ftrata, as will be feen hereafter. 



After the bafon has been uniformly beat in every part, 

 about a gallon of lixiviated wood-aflies may be (ifted over its 

 whole furfaee, and rendered adherent with beaters. 



When the cupell is thus prepared, let down the head on 

 the furnace and make a moderate fire in the fire-hole; which 

 muff be maintained for feveral hours, in order to caule a part 

 of the water, with which the fand has been moiflened, to 

 evaporate. The furplus will be di{fip;tted during the opera- 

 tion, without any inconvenience, by canals of evaporation. 



After a fufticient deficcation, raife the head and fuft'er the 

 cupell to cool a little; fpread out draw or hay over it, and 

 arrange the ingots of lead, placing them gently on it that 

 their weight may not derange the fand : it is to prevent fuch 

 derangement that fi.iaw is emplovpd, as is done in regard to 

 cupeljs of bone-atlies *. When the quantity of lead necef- 

 fary for filling the cupell is arranged in the furnace, let down 



• Infteafi of prifmatic ingots it will be better to caft the lead in henn- 

 fpherical iroa moulds. Pieces of that form are ids liable to danisge ilie 

 •tUi^ll, 



