216 CUPELLATION. 



well covered and protected by the perfect metals j 

 and by uniting with these imperfect metals, it com- 

 municates to them its property of being very easily 

 oxidated. By its vitrifying and fusing property, 

 which it exercises with all its force upon the cal- 

 cined and naturally refractory parts of the other 

 metals, it facilitates and accelerates the fusion, sco- 

 rification, and separation of these metals. The lead, 

 which in this operation is scorified, and scorifies 

 along with it the imperfect metals, separates from 

 the metallic mass with which it is then incapable of 

 remaining united. It floats upon the surface of the 

 melted mass, and becomes semi-vitrified. But the 

 litharge so produced would soon cover the melted 

 metal, and by preventing the access of air would 

 prevent the oxidation of the remaining imperfect 

 metals. To remedy this, such vessels are employed 

 as are capable of imbibing and absorbing in, their 

 pores, the melted litharge, and thus remove it out 

 of the way ; or, for large quantities, vessels are so 

 constructed, that the fused litharge, besides being 

 soaked in, may also drain off, through a channel 

 made in the corner of the vessel. 



Experience has shown that for this purpose, ves- 

 sels made of lixiviated wood or bone-ashes are most 

 proper. These vessels are called cupels^ and this 

 process is called cupellation. The cupels are flat 

 and shallow. The furnace ought to be vaulted, 

 that the heat may be reverberated upon the sur- 

 face of the metal during the whole time of the 

 operation. Upon this surface a crust or dark 

 coloured pellicle is continually forming. In the 

 instant when all the imperiect metal is destroyed, 

 and, consequently, the scorification ceases, the sur- 

 face of the perfect metal is seen, and appears clean 

 and brilliant. This forms a kind of fulguration, or 



i 



