VOL. LXXXVII.] 



PHILOSOPHICAL TRANSACTIONS. 



m 



It appears from the foregoing table, that in the afternoon of the 1st of July, the 

 weight (which was a heavy brass cannon, a 24 pounder, weighing 808 1 lbs. avoir- 

 dupois), was not raised by 12 grs. of powder, but that 13 grs. raised it with an 

 audible though weak, report. That the next morning, July 2d, at 10 o'clock, it 

 was raised twice by charges of 12 grs. That in the morning of the 3d of July, it 

 was not raised by 12 grs., nor by 13 grs. ; but that 14 grs. just raised it. That in 

 the afternoon of the same day, 2 experiments were made with 14 grs. of powder, in 

 neither of which the weight was raised ; but that in another experiment, in which 

 15 grs. of powder were used, it was raised with a moderate report. That in the 

 morning of the 8th July, in 2 experiments, one with 15 grs., and the other with 

 13 grs. of powder, the weight was raised with a loud report; and in an experiment 

 with 12 grs., it was raised with a feeble report. And lastly, that in 3 successive 

 experiments, made in the morning of the 17th of July, the weight was raised by 

 charges of 1 2 grs. Hence it appears, that under circumstances the most favourable 

 to the developement of the force of gunpowder, a charge, = 12 grs., filling ^Vo 

 of the cavity in which it is confined, on being fired, exerts a force against the sides 

 of the containing vessel equal to the pressure of Q43 1 atmospheres ; which pressure 

 amounts to 141465 lbs. avoirdupois on each superficial inch. 



Mr. Robins makes the initial, or greatest force of the fluid generated in the com- 

 bustion of gunpowder, namely when the charge completely fills the space in which 

 it is confined, to be only equal to the pressure of 1000 atmospheres.* It appears 

 however, from the result of these experiments, that even admitting the elasticities 



* The fact however is, that the initial force is really various, gradually increasing as the charge of 

 powder is increased, on account of the superior heat of the explosion. Mr. Robins's experiments were 

 made with only small quantities of powder } and hence he obtained for his initial force the pressure of 

 1000 atmospheres 5 but by increasing the charges considerably, it is found that the said force is gradually 

 increased to near 2000 atmospheres j as appears by Dr. Hutton's Course of Mathematics, vol. 2, 

 p. 352, 353, the 5th edition, anno 1807. 



