VOL. LXXXVII.] PHILOSOPHICAL TRANSACTIONS. 153 



elastic vapour generated in the combustion of gunpowder was confined, and that is, 

 with regard to a curious effect produced on the inferior flat surface of the leathern 

 stopper, where it was in contact with the generated elastic vapour. On removing 

 the stopper, its lower fiat 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 on being exposed to the air. 



The sudden change of colour in this substance, on its being 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 peculiarly 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. Perhaps 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 more 

 curious than an experiment of this kind would be, if it were successful. 



But to proceed to the experiments by which I endeavoured to ascertain the force 

 of fired gunpowder. All the parts of the apparatus being ready, it was in the 

 autumn of the year 1792 that the first experiment was made. The barrel being 

 charged with 10 grains of powder (its contents when quite full amounting to about 

 28 grains), and the end of the barrel being covered by a circular piece of oiled 

 leather, and the flat side of the hemisphere being laid down on this leather, and a 

 heavy cannon, a 24 pounder, weighing 8081 lbs. avoirdupois, being placed on its 

 cascabel in a vertical position on this hemisphere, to confine by its weight the ge- 

 nerated elastic fluid, the heated iron-ball was applied to the end of the vent-tube ; 

 and I had waited but a very few moments in anxious expectation of the event, when 

 I had the satisfaction of observing that the experiment had succeeded. The report 

 of the explosion was extremely feeble, and so little resembling the usual report of 

 the explosion of gunpowder, that the bystanders could not be persuaded that it 

 was any thing more than a cracking of the barrel, occasioned merely by its being 

 heated by the red-hot ball : yet, as I had been taught by the result of former ex- 

 periments not to expect any other report, and as I found on putting my hand on 

 the barrel that it began to be sensibly warm, I was soon convinced that the powder 

 must have taken fire ; and after waiting 4 or 5 minutes, on raising the weight 

 which rested on the hemisphere, the confined elastic vapour rushed out of the 

 vol. xvm. X 



