53 



It is sufficient to admit that pressures which result from the 

 shock exercised on the surface of nitroglycerin are too sudden 

 to distribute themselves uniformly throughout the whole mass, 

 and that consequently the transformation of the energy into 

 heat takes place more especially in the first layers reached by 

 the shock. If this be sufficiently violent, these layers may thus 

 be suddenly raised up to about 200, and they will immediately 

 decompose, producing a great quantity of gases. The produc- 

 tion of gas is, in its turn, so sudden that the striking body has 

 not time to displace itself, and the sudden expansion of the 

 gases of the explosion produces a first shock, doubtless, more 

 violent than the first on the layers situated below. The energy 

 of this new shock changes itself into heat in the layers which it 

 first reaches. It determines their explosion, and this alternation 

 between a shock developing an energy which becomes changed 

 into heat, and a production of heat which raises the temperature 

 of the heated layers up to the degree of a new explosion capable 

 of reproducing a shock, transmits the reaction from layer to 

 layer throughout the entire mass. The propagation of the 

 deflagration thus takes place by virtue of phenomena comparable . 

 to those which give rise to a sound wave ; that is to say, by 

 producing a true explosive wave which travels with a rapidity 

 incomparably greater than that of a simple inflammation, 

 induced by the contact of a body in ignition and effected in 

 conditions under which the gases freely expand as they are 

 produced. We shall define this explosive wave and study its 

 characteristics in Chapter VII. 



4. The reaction induced by a first shock in a given explosive 

 substance propagates itself with a rapidity which depends on 

 the intensity of the first shock, seeing that the energy of the 

 latter transformed into heat determines the intensity of the first 

 explosion, and consequently that of the entire series of consecu- 

 tive effects. Now the intensity of the first shock may vary 

 considerably according to the mode in which it is produced. 

 The effect of the blow of a hammer may vary in its dura- 

 tion, for instance, from yJ to -nyj-<ro f a second, according to 

 whether the blow be given with a hammer with a flexible 

 handle, or with a block of steel, as shown by Marcel Deprez's 

 experiments. 



It follows, then, that the explosion of a solid or liquid mass 

 may develop itself according to an infinite number of different 

 laws, each of which is determined c&teris paribus by the original 

 impulse. The more violent the initial shock, the more sudden 

 will be the decomposition induced, and the more considerable 

 will be the pressures exercised during the entire course of this 

 decomposition. One single explosive substance may therefore 

 give rise to the most diverse effects according to the process of 

 ignition. 



