on the Combuffion of the Diamond, 89 
The focus having been intercepted by an opaque body to 
¢xamine more clofely the {tate of the diamond, no alteration 
was remarked in it, except that it had affumed a yellowifh 
Shade, perfectly like that of tranfparent amber. The atmo- 
{phere beginning to become charged with vapours, the expe- 
riment was difcontinued, in order that we might refume it at 
a more fayourable moment. This momeut occurred the next 
day the roth, and was announced by a rifing of the thermo- 
meters; one of which, expofed to the fun in-the open air, 
rofe to 40 degrees; and the other, expofed to the fun alfo 
under a bell-giafs to compare the interior temperature, rofe 
to 44 degrees. 
The focus was thrown upon the diamond at 28 minutes 
after rr. At 42 minutes after 11 the cone of light was in- 
tercepted, and we faw the diamond red, tranfparent, and fur- 
rounded with a faint radiation. When cooled, its edges ap- 
peared blunted: we obferved in it a black point; but it had 
become white, and had loft the yellow colour acquired the 
day before. 
The experiment could not be refumed till the 15th. We 
began, by noting the height of the interior column of the 
mercury, to calculate, according to the temperature and pref- 
fure, the volume of the aériform fluid remaining under the 
bell; and we judged that it had decreafed about 173 cubic 
centimetres. 
The rays of the fun were bright and ftrong; but the air fo 
much agitated, that while the thermometer under the bell 
was at 44°5, that expofed to the fun in the open air did not 
rife higher than 32°. There was a moment, however, when 
the Juminous cone produced a flight fcintillation on the fur- 
’ face of the diamond.. An opaque body, immediately inter- 
pofed, made it appear red ;_ but more obfcure than on the 
ioth. It was alfo found white after cooling. 
Being aftonifhed that the diamond, when inflamed, as on 
the roth, did not maintain of itfelf the temperature neceflary _ 
for its combuftion, efpecially in oxygen gas, as happens ta 
his experiments made on the diamond with the large lens of Trudaine, 
See Dict, de Chemie de l'Encyclop. Method. Voll. p» 741. 
a 1g metalli¢ 
