STATER OF PHILIP OF MACEDOV. 29 



with' it after the first refilling, we may form some notion 

 of it (•). 



The practice in that city was to take a crucible thir- Described by 

 teen inches high, and five inches wide at the mouth : Hellot. 

 to put a layer of small charcoal three iucbes deep at the 

 bottom, and cover it with a triangular piece of a crucible, 

 fastened by a little lute at each corner, its sides answering 

 to the corners of the crucible: and on this false bottom to 

 place sixty or sixty-live pounds of silver iu long slender 

 ingots, to be melted and purified. The wind-furnace used 

 for this purpose was fourteen inches high, seven in diameter 

 at the grate, and nine at the top. The metal, as it melted, 

 was observed to sink to three inches below the edges of 

 the crucible; and then, when it had acquired a sufficient 

 degree of heat, it was seen to boil like water exposed 

 to a strong fire. In this state it was kept seven or eight 

 hours. 



The elastic fluid, which in this case was evolved from the Artificial be!- 

 charcoal beneath, caused the agitation here mentioned ; ws * 

 the charcoal constituting, as we may say, a kind of bellows 

 ingeniously placed at the bottom of the crucible. 



Charcoal, placed in close vessels of glass or metal, we Charcoal not 



know is not altered, though heated redhot. This we are decomposed 



, , , . ~ , , in close vessel 



taught by theory, and the truth is confirmed by many ex- of glass or me- 



peri'men'ts. But the observation reported by the judicious tai : 

 Hellot equally attests, that in this case the charcoal beneath earthen ones 

 the melted silver is decomposed, and continues to furnish 

 elastic fluid ; since this learned chemist found, that silver 

 kept in the same degree of heat, without any charcoal 

 beneath, lias a tremulous motion at its surface, and pro- 

 ceeds from the centre to the sides and back again, but does 

 not boil with such noise*: whence then comes the elastic 

 fluid ? 



Priestley, the founder of modern pneumatic chemistry by This found bv 

 an immense number of facts, demonstrates in the most evi- Priestley. 

 dent manner, what has since been confirmed by many other 

 experiments, that earthen vessels, heated to such a degree 

 as to give a passage to light, are filters, or rather sieves, 



* The silrer has merely an undulating and circulatory motion. 



giving 



