43G Some Experiments on ike Comlustion of the Diamond. 



of the volume of the gas, there is every reason to believe, tha* 

 the water is formed by tlie combustion of hydrogen existing in 

 the charcoal ; and experiments which I have referred to, or de- 

 tailed in my third Bakorirai Lecture, prove the presence of hy- 

 drogen in common charcoal ; and as the charcoal from the oil of 

 turpentine left no residuum, no other cause but the presence of 

 hydrogen can be assigned for the dimiimtion occasioned in the 

 volume of the gas duiiug its combustion. 



M. Gnyton de Morvcau* has noticed the production of water 

 during the combustion of jilumbago from Keswick ; and from 

 these experiments it is most probable that it is formed in the 

 process of combustion, for it is unlikely that water should re- 

 main in union with plumbago at a red heat; and in the various 

 experiments that I have made on the ignition of plumbago by 

 Voltaic electricity, I have never jjerccived the separation of anv 

 moisture, or the production of any gas ; so that it seems most 

 likely that it contains intimately combined hydrogen. It cannot 

 be supposed that water exists in it in union with oxide of iron, 

 for in this case there would be no obvious cause for the diminu- 

 tion of the' volume of the gas; and all analogy is in favour of 

 the conclusion that the iron is in a metallic state. 



The general tenor of the results of these experiments is op- 

 posed to the opinion, that common carbonaceous substances 

 differ from the diamond by containing oxvgen ; for in this case 

 tliey ought to increase and not diminish the volume of oxygen : 

 nor, on the other hand, is it favourable to the supposition that 

 the diamond contains oxygen, for the difference in the quantity 

 of carbonic acid produced in the different experiments, is no 

 more than may be reasonably ascribed to the generation of vva- 

 tw, in the combustion of the common carbonaceous substances; 

 and the results of the experiments, to which I have referred in 

 the beginning of this paper on the action of potassium on the 

 diamond, may be easily accounted for from other circumstancesf. 



That charcoal is more inflammable than the diamond may be 

 explained from the looseness of its texture, and from the hydro- 

 gen it contains ; but the diamond appears to burn in oxvgen 

 with as much facility as plumbago, so that at least one distinc- 

 tion supposed to exist between the diamond and common car- 

 bonaceous substances is done away by these researches. 



A fact which I formerly noticed, the blackening of diamond^ 



* Annaks de Cfiimie, tome Ixxxiv. p. 341. 



t See Bukcriiui Lecture for 11308. Potiissium decomposes the silica in 

 gliiss by being litatol in contact witli it ; and in tbe case in whicli cqual- 

 fjuantities (jf potassium were long heated in jjlass tubes, the one in contact 

 with diamonds, the otlier alone, that in contact witli the diamonds must 

 h.ivc iicted upon a inucli greater surluce ol" glass. 



by 



