446 New Facts concerning the Diamond. [October, 



rapidly disappeared, but could be restored by again heating 

 it. On examining a rose-coloured diamond, expected by M. 

 Coster to acquire a deeper tint upon exposure to heat, it 

 was found, on the contrary, that the effect of the operation 

 was to deprive it of colour, which it afterwards gradually 

 regained. Several experiments were made by von Baumhauer, 

 in concert with M. Daniels, upon grey diamonds, in the 

 hope that the effect of heat would, by removing the colour, 

 add to their value ; but unfortunately the desired result was 

 not achieved, as the diamonds presented after treatment the 

 same greyish aspect as before. 



Very different effects are obtained when, instead of heat- 

 ing the diamond in an atmosphere of hydrogen, it is heated 

 in contact with the air. It is unnecessary to employ a 

 white-heat, or to subject the diamond to it for so long a 

 time, in order to render it dull, and consequently opaque ; 

 this being the result of positive combustion, which is proved 

 by its loss of weight after the operation. This combustion 

 is, however, quite superficial, as shown by M. Daniels, who 

 found that when re-polished, the diamond recovered com- 

 pletely its transparency and its water ; it was, moreover, 

 remarked by M. G. Rose that if the diamond which had 

 become dull was moistened with essence of turpentine, it 

 reassumed its transparency, and retained it as long as its 

 surface continued moist. 



The diamond may also be heated in an atmosphere of 

 oxygen, by introducing a current of that gas into the 

 crucible through the small platinum tube before mentioned ; 

 in this case the stone attains a vivid state of incandescence, 

 and burns with a dazzling flame long before the platinum 

 crucible has attained a reddish-white heat. In most cases, 

 after the lamp has been withdrawn and the crucible is no 

 longer red-hot, the diamond continues to burn for some 

 time, and presents an appearance of vivid light upon a dark 

 ground. When the diamond is very small combustion may 

 even continue until it is entirely consumed, and it is then 

 seen to dart a more vivid flame at the last moment, like a 

 burning match, the instant previous to extinction. When 

 the stone is of considerable size, the heat produced by com- 

 bustion is insufficient to maintain it after the removal of the 

 lamp, and it ceases in a few moments notwithstanding the 

 oxygen which continues to flow into the crucible. 



Although this last experiment has been repeated several 

 times by these experimentalists, no other result has been 

 observed than tranquil combustion of the diamond ; such 

 phenomena as turning black, transformation into coke, 



