Additional Notes. 493 



red. Thus it appears that the rays towards the mlcldlc of the 

 spectrum possess the greatest illuminating power, and those at 

 the extremity the least; and that the illuminating power of 

 the rays gradually diminishes from the middle of the spectrum 

 towards its extremities." — Ibid. 



Carbon and Diamond the same. p. 96. 



As the diamond is not affected by a considerable heat, it 

 was for many ages considered as incombustible. Sir Isaac 

 Newton observing that combustibles refract light more 

 powerfully rhan other bodies, and that the diamond possesses 

 this property in great perfection, suspected it, from that cir- 

 cumstance, to be capable of combustion. This singular con- 

 jecture was verified, in 1694, by the Florentine Academicians, 

 in the presence of Cosmo III. Grand Duke of Tuscany. 

 By means of a burning-glass they consumed several diamonds. 

 Francis I. Emperor of Germany, afterwards witnessed the 

 destruction of several more in the heat of a furnace. These 

 experiments were repeated by Rouelle, Macquer, and 

 Darcet, who proved that the diamond was not merely eva- 

 porated, but actually burnt, and that if air was excluded it 

 underwent no change. 



No attempt, however, was made to ascertain tlie product 

 till 1772. Lavoisier, in a memoir published that year, 

 showed that when the diamond is burnt 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 without leaving any residuum, and in a manner ana- 

 logous to charcoal. This experiment was repeated with more 

 precision by Mr. Tennant, in 1797. (See P/iilos. Trans. 

 for 1797.J The conclusion which he drew from it was, that 

 \vhen diamond is burnt, the whole of the product is carbonic 

 acid gas ; that a given weight of diamond yields just as much 

 carbonic acid gas as the same weight of charcoal ; and that 

 diamond and cliarcoal are both composed of the very same 

 substance. Or rather, to speak more precisely, diamond is 

 pure carbon, while charcoal is a compound of carbon, or 

 diamond and oxygen, or it is what tine French call an oxi/d 

 of diamond. Hence the difference of colour, hardness, spe- 

 cific gravity, and electrical properties, between common char- 

 coal and the precious stone called diamond. — Tiioimpsok'^' 

 Chemistry. 



