34 
COMBUSTIBILITY OF GASES. 
tion in every chemical action*. We must recollect, that water 
is present in the oxymuriatic as well as in every other gas 5 
and, by the experiments of Priestley, Kirwan, Bertbollet, 
Cruickshank, &c. it is put beyond doubt, that charcoal, heated 
as long as possible, contains still a quantity of hydrogen, of 
which the decomposition ought to follow j and, as it does not, 
the reason given is insufficient. 
Investigation 9- I will examine this subject rather more fully. I think 
i)f the cause. the true cause of the non-decomposition lies in the great dila- 
tation to which the oxymuriatic gas is subjected by the heated 
charcoal. In this case it comports itself like the hydrogen in 
my first experiment. At a certain degree of expansion it 
can no longer be decomposed. Neither do I doubt, as a con- 
sequence of what has preceded, that oxigen gas can freely 
pass through ignited charcoal, provided that degree of dilatation 
be acquired, which may be considered as the limit of combus- 
tion of this gas, whether that degree be produced by an elevated 
temperature, or by any other circumstance. 
Difference be- 10 . Another well-known phenomenon, not sufficiently ex- 
fecTof ^an P^ nec ^ as prevented by hydrogen gas, which, notwithstanding 
nited body and its great combustibility, does not take fire by an ignited body, 
flame. though it does by flame. The following observations, compared 
with our theory,may, perhaps, throw some light upon the subject. 
When a well-ignited piece of charcoal is taken up with a wire, 
and the finger is brought within an inch of it, the heat is 
scarcely to be borne j but we can easily hold the finger at half 
that distance from a lighted candle, without perceiving any 
sensible heat. 
In this case it appears, that flame insulates the heat it derives 
ana ion. f rom the burning wick, or that it is carried upwards by the 
* See my Memoir in the Annates de Cliimie, vol. LXII, the works 
of Scheele, edited by Hermbstadt, p. 228 ; and Mrs. Fulham’s Essay on 
Combustion, London, 1794. — G. 
To the above note M. Vogel adds^ 
M.Ruhland, of the Academy of Munich, who is at this time at 
Paris, has published an interesting Memoir in the Chemical Journal of 
Schwrigger, on the necessary presence and fixation of water during 
the act of combustion. He has shewn, that a great number of com- 
bustible bodies cannot burn in well dried air, and that water is very 
much concerned in the union of oxigen with them. 
flame. 
