450 Some Experhne?ils on ihe Comhustion of the Diamond, 



a gas having tlie same obvious qualities, a number of conjec- 

 tures have been formed to exj)l;iin the remarkable differences in 

 the sensible qualities of these bodies, by supposing some minute 

 difference in their chemical composition : these conjectures have 

 been often discussed, it will not be necessary therefore to dwell 

 upon them. MM. Biot and Arago, from the high refractive 

 power of the diamond, have supposed that it may contain hy- 

 drogen. I ventured to suggest in my third Bakerian Lecture, 

 from the circumstance of its nou-conduciing power, and from 

 the action of potassium upon it, that a minute j)ortion of oxygen 

 may exist in it ; and in my Account of some new J^xperiments 

 on the fluoric Com])onnds*, I hazarded the idea that it Tuight 

 be the carbonaceous ])rin<Mple combined with some new light 

 and subtile clement of the class of supporters of combustion. 

 M. Guyton de Morveau, who conceived he had jiroved by ex- 

 periments made fourteen years ago, that common carl)onaceous 

 substances were oxides of diamonds, from his last researches, 

 conducted in the same manner as those of Messrs. Allen and 

 Pepys, seems still inclined to adoj)t this opinion, though in ad- 

 mitting a much smaller quantity of oxygen than he originally 

 supposed in charcoal ; and he considers the diamond as pure 

 carbonaceous matter, containing, possibly, some atoms of water 

 of crystallization. 



I have long had a desire of making some new experiments on 

 the combustion of the diamond and otiicr carljonaceous sub- 

 stances ; and this desire was increased by tlie new facts ascer- 

 tained with respect to iodine, which by uniting to hydrogen af- 

 fords an acid so analogous to muriatic acid, that it was for some 

 time confounded with that substance. My oljject in these ex- 

 periments was, to examine minutely whether any peculiar mat- 

 ter was separated from the diamond during its combustion, and 

 to determine whether the gas, formed in this process, was pre- 

 cisely the same in its minute chemical nature, as that formed in 

 the combustion of common charcoal. I have latelv been able 

 to accom])lish my wishes ; I sliall now have the honour of com- 

 municating my results to the Royal Society. 



During a stay that I made at Florence in the end of March 

 £4nd beginning f)f April, I made several experiments on the com- 

 bustion of the diamond, and of plumbago, l)y means of the great 

 lens in the Cabinet of Natural History; the same instrument as 

 that employed in the hrst trials on the action of the solar heat 

 on the diamond, instituted by Cosmo III. Grand Duke of Tus- 

 cany; and I have since made a series of researches on the com- 

 bustion of different kinds of charcoal at Rome, in the laboratory 



' Phil. Trans, for 10M-. part i. p. 72— Pliil. Mac:, p. 93. 



of 



