1 873.] New Facts concerning the Diamond. 443 



To take the average of such results, which in the author's 

 opinion is not permissible, the corrected density of the 

 diamond, as compared with water at 4 C, would be 



3'5i835- 



The omission of Nos. 6 and 7 is intentional, those dia- 

 monds being permeated with fissures, possibly containing 

 air, which would alter their specific gravity. 



It is considered that the density 3*51432, declared by M. 

 Schrotter to be the lowest of his results, is too small ; for, 

 amongst the diamonds which he examined, some had 

 blemishes or fissures, whilst in those which were without 

 defect he also obtained much higher numbers ; for instance, 

 3*51869 in a perfectly colourless diamond, 3*51947 in one 

 of pale violet colour. Judging from all known results, M. 

 von Baumhauer believes the density of a pure diamond 

 should not be much less than 3*52. 



The figures contained in the Table also show that the 

 density of boart, or the globular diamond, seldom exceeds 

 3*50, whilst carbonado possesses a considerably lower 

 specific gravity, being probably a porous diamond, a con- 

 clusion confirmed, moreover, by examination with a lens. 

 The higher density found in Nos. 16 and 17 prove that 

 these specimens are not carbonado, but some intermediate 

 variety between that and the true diamond. 



When shielded from contact with the air, the diamond 

 may be exposed to the highest temperature of our furnaces 

 without undergoing alteration, at least in the case of the 

 colourless diamond ; of coloured diamonds more will be 

 said hereafter. The experiment by which this fact is 

 generally demonstrated is conducted as follows : the dia- 

 mond is placed in a small Hessian crucible and covered 

 with closely compressed magnesia ; this is introduced into 

 another crucible which is completely filled up with well 

 pressed graphite, and then the whole is subjected for a long 

 time to the strongest heat obtainable in a porcelain furnace. 

 This experiment was successively repeated by Morren, 

 Schrotter, and others, who ascertained that, notwithstanding 

 the excessive heat to which the diamond was subjected, it 

 underwent no change either in shape or quality ; Schrotter, 

 however, remarked that the surface became slightly dull. 

 Similar experiments were made at Berlin by the late 

 Gustav Rose, with the co-operation of Dr. Siemens. A 

 crystal of diamond, enclosed in a piece of dense coke and 

 placed in a plumbago crucible packed with charcoal powder, 

 was heated for half an hour in one of Siemens's regenerative 

 furnaces to the temperature at which cast-iron melts without 



