1900.] on Some Modern Explosives. 343 



course. The whole of the charge is consumed in something less than 

 fifteen thousandths of a second. 



In the case of the blue curve the maximum pressure indicated is 

 obtained in the way I have described, and is approximately correct — 

 about nine tons per square inch. The rapidity with which this 

 considerable charge parts with its heat by communication to the 

 explosion vessel is very striking. In four seconds after the explosion 

 the pressure is reduced to about one-half, and in twelve seconds to 

 about one-qrarter. 



1 now show you (Fig. IX.) similar curves for cordite ' 35 inch in 

 diameter, or about fifty times the rifle cordite section. Here you see 

 that the time taken to consume the charge is longer. The effect of 

 inertia is still very marked, although much reduced. The true maxi- 

 mum pressure is a little over 8*5 tons, but after the first third of a 

 second the two curves run so close together that they are indistin- 

 guishable. 



Again you see the pressure is reduced by one-half in four seconds, 

 and in a little more than twelve seconds again halved. 



The last pair of curves I shall show you (Fig. X.) was obtained 

 with cordite 0*6 inch in diameter, or nearly 150 times the section of 

 the rifle cordite. With this cordite the combustion has been so slow 

 that the effect of inertia almost disappears, it is reduced to about half 

 a ton per square inch ; the maximum being nearly the same as in the 

 last set of experiments. The time of combustion indicated I have 

 called slow, but it is about • 06 of a se cond, and the whole of the 

 experiments show a most remarkable regularity in their rate of cooling, 

 the pressures at the same distance of time from the explosion being 

 in all ca^es approximately the same, as indeed they ought to be, the 

 density being the same and the explosive the same, the only difference 

 being the time in which the decomposition is completed. 



It appears to me that, knowing from the experiments I have 

 described, the volume of gas liberated, its composition, its density, 

 its pressure, the quantity of heat disengaged by the explosion, and 

 knowing all these points with very considerable accuracy, we should 

 be able, from the study of the curves to which I have drawn your 

 attention, and which can be obtained from different densities of gas, 

 to throw considerable light upon the kinetic theory of real, not ideal, 

 gases, at temperatures and pressures far removed from those which 

 have been the subject of such careful and accurate research by many 

 distinguished physicists. 



The question, as I have said, involves some very considerable 

 difficulties, nevertheless I am not without hoi)e that the experiments 

 I have been describing may, in some small degree, add to our know- 

 ledge of the kinetic theory of gas. 



That wonderful theory faintly shadowed forth almost from the 

 commencement of philosophic thought, was first distinctly put for- 

 ward by Daniel Bernoulli early in the last century. In the latter 

 half of the century now drawing to a close the labours of Joule, 



