DIAMOND: INCOMBUSTIBLE ASH 117 



subjected to electric sparking, such a change is observed, but in neither of these cases can the 

 blackening possibly be due to a sooty coating derived from the vapours of the source of heat. 

 It is stated by Jaquet that a diamond placed in the electric arc given by one hundred 

 Bunsen cells softens and becomes converted into a coke-like mass, the specific gravity of 

 which is 2-678, while that of the diamond experimented upon was 3'336. He observed 

 further, that whereas the material of diamond is a bad conductor of electricity, when converted 

 into coke or graphite it becomes a good conductor. 



Similar observations have been made by Gassiot, who has stated that before 

 the alteration of diamond into a coke-like mass it softens and has the appearance of a 

 body about to melt. Other statements respecting the melting of diamond, or of appearances 

 referable to this change of state, are to be found in scientific literature. Berzelius reports 

 that he observed a bubble on the surface of a burning diamond, and Clarke saw bubbles 

 on the surface of a diamond when strongly heated in the oxyhydrogen flame. Other 

 observers, on the other hand, under exactly similar conditions, have failed to notice any 

 appearance of the kind, and in the absence of unanimous testimony it is still doubtful 

 whether diamond does really fuse at high temperatures. Observations of the kind quoted 

 are not altogether free from error ; the rounding of the edges and corners of a partly- 

 consumed diamond crystal would give it the appearance of having been fused ; the rounding 

 is, however, due to the fact that these prominent portions burn more rapidly than do the 

 faces. The Emperor Francis I. sought to obtain a large diamond by fusing together 

 several small ones ; the attempt was, however, a complete failure, and the diamonds were 

 burnt. 



Probably the highest temperature to which diamond has been artificially subjected was 

 reached in the experiments of Despretz, who employed for the purpose the electric spark 

 given by five hundred to six hundred Bunsen cells. He reported that in the absence of air 

 the usual change into graphite took place, and that if the heating was sufficiently prolonged 

 beads of fused material were formed. Similar beads were also obtained from other varieties 

 of carbon, but it is possible that these consisted of the mineral residue fused into a hard 

 mass. If, however, this were the case, it would appear that the carbon had been volatilised, 

 since combustion could not have taken place. It is very desirable that the researches of 

 Despretz should be confirmed by further observation. 



The whole of the substance of a perfectly colourless and transparent diamond is 

 converted, when exposed to sufficient heat, into carbon dioxide, and no residue whatever 

 remains behind. In the case of a deeply coloured or otherwise impure diamond combustion 

 is not so complete, a small amount of incombustible ash remaining behind after the 

 diamond has been converted into carbon dioxide. This residue consists of inorganic 

 impurities differing in chemical composition in different stones ; these have been enclosed 

 in the diamond during its growth, and are the cause of the colour or cloudiness of the 

 stone. 



This residual ash varies very considerably in amount in different stones. In the 

 purest stones it is almost imperceptible, while in less pure stones it varies from tj^htt to -5^^ 

 of the total weight (0-05 to 0-2 per cent.). The largest amount of ash, amounting to as 

 much as 4'2 per cent., is present in carbonado, a peculiar variety of black, porous diamond 

 found in Brazil. These impurities are often evenly distributed throughout the crystal. 

 Occasionally, however, they are collected together at one or more points, which then appear 

 coloured and cloudy, the surrounding portions being colourless and transparent. Such 

 imjiurities in the diamond are isolated during combustion, but are more or less altered in 

 character by the heat, sometimes being fused into beads, as mentioned above. The uniform 



