I 



I 



Mr. L. Thomas on the Action of Fired Gunpowder. 367 



chamber to be made similar in form to, but of twice the linear dimen- 

 sions of, the former ; he then placed a cast-iron ball of 6 inches 

 in diameter upon the orifice of this chamber, which was filled with 

 powder ; upon firing the latter, the ball was driven up to a height of 

 1 1 feet, that is to say, to double the height of the smaller ; the state of 

 the metal in which the chamber was formed also showed the increase 

 in the initial force of the powder : this is considered to be sufficient 

 proof that the last two of the above-mentioned propositions are as 

 incorrect as the first. 



Assuming the initial force of the powder to be of an impulsive 

 nature, it is not difiicult to understand the increase of force shown 

 in the last-named experiment, inasmuch as a certain time being re- 

 quired for the complete conversion of the powder into an elastic fluid, 

 a quantity contained in a chamber of a similar form, but of greater 

 linear dimensions than another, must ignite in a less comparative 

 time, the linear dimensions increasing in the ratio of the first power, 

 and the quantity of powder increasing in the ratio of the third power. 

 So that the flame will traverse a larger quantity in comparative less 

 time. 



Thus it appears that the powder which inflames more rapidly has 

 a much greater initial force, being vaove concentrated in its action ; a 

 quick burning powder therefore is better for ordnance of small length, 

 such as mortars and iron howitzers. The diff'ereut results produced by 

 powder of different quality have, according to the author, been en- 

 tirely overlooked in the hitherto received theory. This theory, which 

 considers the secondary force, namely, the elasticity of the fluid only, 

 and takes no account whatever of the enormous impulsive, or initial 

 force, produced by the sudden conversion of the powder into an elastic 

 fluid, is that which regulates the system upon which ordnance are at 

 present constructed ; hence the reason why large guns are so liable 

 to burst, so much so, that it has been said that no gun larger than a 

 32-pounder is safe to fire. From the variety of experiments made 

 by the author, he arrives at the conclusion, that when powder is of the 

 same quality, and confined in chambers of similar form, but of differ- 

 ent sizes, the initial force varies, within certain limits, in the ratio of 



-7 , where w is the weight of the powder and w' of the ball. 



Thus were this new theory recognized, the question of the in- 

 crease of strength with increased thickness of metal, would wear an 

 entirely new aspect. So far from the metal in large guns diminishing 

 in strength in the proportion assumed, it will be a matter for inquiry 

 how it resists the great strain to which it is subjected, rather than 

 why it yields ; for we fiud from the experiments described above, 

 that a (iS-pounder gun, which has a calibre of twice the diameter of 

 a 9-pounder gun, must, when tired with the same proportionate 

 charge of powder as the latter, continually be subject to as great a 

 strain as the latter would suffer if always fired with the proof charge, 

 which is three times the quantity of the ordinary service charge. 



