21 S 4 CcmlujTion of Diamonds. [Bock VI, 



a high degree of heat, entirely difappear at thelnftarit 

 that an appearance of corabnftion is obferved. M. 

 Cadet"- expofed diamonds, in covered and luted* cru- 

 cibles to the violent "hdat of a forge during two hours, 

 by vyhich the diamonds only loft one fixteenth part of 

 their weight, he was therefore of opinion, that the 

 confurnption of diamonds in open veffels is not a true 

 volatilization, but merely an exfoliation occafioned by 

 the expanfion of the air contained between the laminas 

 of the 'diamond, by which it is broken into portions 

 fo minute as to efcape obfervation. M. D'Arcet 

 oppofed to die above explanation, the efcape of the 

 fubftance of the diamonds through the moft folid por- 

 celain crucibles, and the luminous appearance noticed 

 by Macquer, and which was afterwards obferved by 

 M. Roux to be an actual flame. It was, indeed, evert 

 found, that diamonds inclofed in a ball of porcelain 

 earth, and expofed to heat, were totally confumcd; 

 the ipace which the diamond occupied was found 

 empty j no traces of it could be difcovered, and yet 

 the ball of porcelain, which was hardened by the heat, 

 \vas apparently entire^ This experiment, according 

 to Fourcroy, was frequently repeated with the fame 

 extraordinary refult. It Was found, however, that if 

 the diamond was embedded in charcoal, and carefully 

 inclofed in feveral crucible^ placed within each other, 

 and the whole covered with cement, it did not 'dif- 

 appear from expofure to a very violent heat ; it was 

 only rendered black at its furface, and when this cruft 

 \vas taken cff, it appeared in its original fplendor. It 

 was therefore very juftly concluded, that perfect ex- 

 clufion from vital air is fufncient to prevent the con- 

 furnption of the diamond, as well as of all other in- 



* Luting is a land of earthy cement ufed by chemifts, and 

 formed in different ways. 



flammable 



