96 DIAMONDS AND 



a fact soon to be proved, and he went still further, and wTOte that 

 probably it was an "unctuous substance coagulated." By unctu- 

 ous substance, he meant such as camphor, spirit of turpentine, 

 gums, etc. At a later period, Brewster still further established the 

 connection between a high degree of inflammability and a great 

 refractive force, by the high refractive power he detected in phos- 

 phorus. 



Towards the end of the 17th century, Boyle, as predicted by 

 Newton, demonstrated that under an excessive heat the Diamond 

 disappeared. A little later, in 1694, a diamond was destroyed at 

 Florence by means of a " burning glass," and the spectators saw 

 with wonder it first become smaller and then entirely disappear, 

 under the action of the rays of the sun. It was not, however, 

 till nearly a century afterwards that the investigation of the nature 

 of the Diamond by the aid of heat was seriously prosecuted. In 

 1 771, before a distinguished company of savants, Macquer burnt 

 a fine Diamond in his laboratory in Paris. Immediately a great 

 amount of discussion arose, some experts maintaining that fire 

 had no effect on the Diamond ; amongst the most notable was 

 M. Blanc, a celebrated jeweller of Paris, who, to prove his asser- 

 tion, proposed to submit a diamond to the heat of a furnace for 

 three hours. This experiment was performed in the laboratory of 

 a chemist named Rouelle, and attracted a large number of men 

 of science and jewellers. The stone was placed in a crucible, 

 which was filled with lime, and submitted to the fire, and Blanc 

 had to return home without his diamond, much to the delight of 

 the savants. After this, a clever lapidary of the name of Maillard 

 came to the rescue of his confi-ere, and offered to submit three 

 diamonds to any fire, and for any length of time. This challenge 

 being accepted, Maillard placed his diamonds in the bowl of a 

 clay tobacco-pipe, covered them up with charcoal-dust, so as to 

 exclude air, closed the top of the bowl with an iron cover, and 

 placed it in a crucible filled with powdered chalk. This was sub- 

 mitted to such a heat that at the end of four hours the crucible had 

 become a vitrified mass. The fire was then stopped, and on the 

 mass cooling, Maillard, amidst the jokes of the spectators, who 

 recommended him to look up the chimney for his diamonds, 

 broke open the crucible, and there in the centre was the tobacco- 



