Combustion of the Diamond. 567 
M. Guyton de Morveau* has noticed the production of 
water during the combustion of plumbago 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 remain 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 perceived the 
separation of any moisture, or the production of any gas ; so 
that it seems most likely that it contains intimately combined 
hydrogene. 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 diminution 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 
opposed to the opinion, that common carbonaceous substances 
differ from the diamond by containing oxygene; for in this 
case they ought to increase and not diminish the volume of 
oxygene: nor, on the other hand, is it favourable to the sup- 
position that the diamond contains oxygene, for the difference 
in the quantity of carbonic acid produced in the different ex- 
periments, is no more than may be reasonably ascribed to the 
generation of water, in the combustion of the common carbo- 
naceous substances; and the results of the experiments, to 
which I Iiave referred in the beginning of this Paper on the 
action of potassium on the diamond, may be easily accounted 
for from other circumstances, -f 
* Annales de Chlmie, Tome LXXXIV. page 241. 
f See Bakerlan Lecture for 1808. Potassium decomposes the silica in glass by 
being heated in contact with it, and in the case in which equal quantities of potassium 
4 D 2 
