30 STAfER OF PnitIP OF MACEDOtt, 



The process giving admission even to the external air*. Thus caloric and 

 «xpl»»ned on light penetrating the bottom of the crucible, and with them 

 the air, attracted chemically by the charcoal within, its 

 oxigen, coming into contact with the incandescent charcoal, 

 inflames a portion of it, combines with it and caloric, and 

 forms carbonic acid. This elastic fluid, through the unin- 

 terrupted action of the fire, acquires sufficient force, to 

 overcome the pressure of a column of seven inches of liquid 

 silver above if, and passes through it, agitating it violently. 

 The small residue of lead, which was combined and diffused 

 throughout the mass, being brought by the continual agi- 

 tation into contact with the carbonic acid gas and the at- 

 mosphere (the latter, and perhaps the former, being decora- 

 posed by a superior affinity from the concurrence of cir- 

 cumstances), is oxided, and, from the diminution of its 

 specific gravity, is compelled to occupy the upper surface. 

 The fused ox- In fact, Hellot observed a kind of yellowish oil rise-fcia* 



Me of lead the interior of the melted silver, and float on it. This oil 



rose like an 



eii. was a pure oxide of lead in fusion ; formed by the contact of 



the continually renewed atmospheric air. The refiners col- 

 lect this melted oxide, by enveloping and absorbing it with 

 glass or a meagre earth; this earth being removed more 

 readily from the silver it covers, and then the metal remains 

 pure and limpid. 

 The process of If we refer to this method the process of Agatharchides, 

 Agatharchides re p 0ite( j aDove> though very imperfectly, we may suppose, 

 that the barley, or its meal, was employed instead of char- 

 coal, to form what the Lyonese call the soul of the crucible ; 

 that it was placed at the bottom of the crucible, and retained 

 there by a cover (whence probably the expression of & closed 

 crucible) ; and that on this was poured the gold fused with 

 a little lead, to vitrify the base metals it might contain, and 

 common salt, and sulphuret of antimony or of lead, to seize 



* This is denied hy many ahle chemists, who assert, that Priestley 

 ■was mistaken in his idea; and that the air, in his experiments, was 

 admitted through minute cracks in his vessels, imperceptible to the 

 naked eye. Still this does not invalidate the reasoning of Mr. Fabbroni ; 

 for, if this be the true state of the case, air might be admitted to the 

 charcoal in this proceas through similar cracks in the bottom of the 

 crucible C. 



the 



