the Force of fired Gunpowder. 251 
observation more, relative to the particular appearances which 
attended the experiments in which the elastic vapour generated 
in the combustion of gunpowder was confined, and that is, with 
regard to a curious effect produced upon the inferior flat surface 
of the leathern stopper, where it was in contact with the gene- 
rated elastic vapour. Upon removing the stopper, its lower 
flat surface appeared entirely covered with an extremely white 
powder, resembling very light white ashes, but which almost 
instantaneously changed to the most perfect black colour upon 
being exposed to the air. 
The sudden change of colour in this substance upon its be- 
ing exposed to the air, has led me to suspect that the solid 
matter found in the barrel was not originally black, but that 
it became black merely in consequence of its being exposed to 
the air. The dirty grey colour it appeared to have immediately 
on being drilled out of the cavity of the bore, where it had fixed 
itself, seems to confirm this suspicion. An experiment made 
with a very strong glass barrel would not only decide this 
question, but would most probably render the experiment pe- 
culiarly beautiful and interesting on other accounts; and I 
have no doubt but a barrel of glass might be made sufficiently 
strong to withstand the force of the explosion. Whether it 
would be able to withstand the sudden effects of the heat, I own 
I am more doubtful ; but as the subject is so very interesting, 
I think it would be worth while to try the experiment. Per- 
haps the apparatus might be so contrived as to set fire to the 
powder by the solar rays, by means of a common burning 
glass; but even if that method should fail, there are others 
equally unexceptionable, which might certainly be employed 
with success ; and it is hardly possible to imagine any thing 
MDCCXCVII. L 1 
