Chap. II.] Ciicmical Philosophij. 123 



duke of Tuscany. By means of a burning glass 

 they consumed several diamonds. Francis I, em 

 peror of Germany, afterwards witnessed tlie de- 

 struction of several more in the heat of a furnace. 

 These experiments were repeated by Ruueile, 

 Macquer, and Darcet, who proved that tlie dia- 

 mond was not merely evaporated, but actually 

 burnt, and that if air was excluded it underwent no 

 change. 



No attempt, however, was made to ascertain the 

 product till 1772. Lavoisier, in a memoir pub- 

 lished that year, showed, that, when the diamond is 

 \y\xn\t, carbonic acid gas is obtained; and that there 

 is a striking analogy between it and charcoal. In 

 1785 Guyton-Morveau found that the diamond is 

 combustible when dropped into melted nitre ; that 

 it burns v/ithout leaving any residuum, and in a 

 manner analogous to charcoal. This experiment 

 was repeated with more precision by Mr. Tennant, 

 in 1797. The conclusion which he drew from it 

 was, that, when diamond is burnt, the whole of 

 the product is carbonic acid gas; tiiat a given 

 weight of diamond yields just as much carbonic 

 aoid gas as the same weight of charcoal ; and that 

 diamond and charcoal are both comi)Osod of the 

 very same substance — or rather, to speak more 

 precisely, diamond is pure carbon, whih^ chan^oal 

 is a compound of carbon, or diamond, and oxygen, 

 or it is what the French call an o.rijd of diamond. 

 Hence the dilFerence of colour, hardness, specific 

 gravity, and electrical properties, between com- 

 mon charcoal and the precioiLS stone called dla- 

 mond. 



Since the commencement of the eighteenth cen- 



