the Force of Fired Gunpowder. 133 



tough hammered iron, the area of whose transverse 

 section was only I-/JIQ of an inch, was able to sustain a 

 weight of 119 Ibs. avoirdupois without breaking. This 

 gives 63,466 Ibs. for the weight which a cylinder of 

 the same iron whose transverse section is one inch 

 would be able to sustain without being broken. 



The area of the fracture of the barrel before men- 

 tioned was measured with the greatest care, and was 

 found to measure very exactly 6^ superficial inches. If 

 now we suppose the iron of which this barrel was formed 

 to be as strong as that whose strength I determined 

 (and I have no reason to suspect it to be of an inferior 

 quality), in that case the force actually employed in 

 bursting the barrel must have been equal to the pressure 

 of a weight of 412,529 Ibs. For the resistance or co- 

 hesion of one inch is to 63,466 Ibs. as that of 6-|- inches 

 to 412,529 Ibs. ; and this force, so astonishingly great, 

 was exerted by a body which weighed less than 26 grains 

 Troy, and which acted in a space that hardly amounted 

 to y 1 ^ of a cubic inch. 



To compare this force exerted by the elastic vapour 

 generated in the combustion of gunpowder, arid by 

 which the barrel was burst, to the pressure of the 

 atmosphere, it is necessary to determine the area of a 

 longitudinal section of the bore of the piece. Now the 

 diameter of the bore being ^ of an inch, and its length 

 (after deducting 0.15 of an inch for the length of the 

 leathern stoppers) 2 inches, the area of its longitudinal 

 section turns out to have been |- an inch. And if now 

 we assume the mean pressure of the atmosphere = 15 

 Ibs. avoirdupois for each superficial inch, this will give 

 7|- Ibs. for that upon a surface = |- inch, equal to the area 

 of a longitudinal section of the bore of the barrel. 



