534 CONCLUSIONS. 



same time the easiest and the strictest, and it is then that the 

 results it offers are most far reaching, theoretically speaking. 

 This study enables us, in fact, to show the existence of a new 

 kind of undulatory movement of a compound order, that is to 

 say, produced in virtue of a certain concord of physical and 

 chemical impulses, within a substance under transformation. 

 In the sonorous wave the energy is weak, the excess of pressure 

 stands at the minimum, and the velocity is determined by the 

 mere physical constitution of the vibrating medium. On the 

 other hand, it is the change in the chemical constitution which 

 propagates itself in the explosive wave, and which communicates 

 to the system an enormous energy and considerable excess of 

 pressure. Like phenomena may become developed both in 

 solids and in liquids. 



This wave propagates itself uniformly with a velocity depend- 

 ing essentially on the nature of the explosive mixture, and 

 which is almost independent of the diameter of the tubes, except 

 when these latter are capillary. It is equally independent of 

 pressure, a fundamental property which determines the general 

 laws of the phenomenon. 



Finally, the energy of the translation of the molecules of the 

 gaseous system produced by the reaction, and containing all the 

 heat developed by such reaction, is in proportion to the energy 

 of the gaseous system itself, containing merely the heat which 

 it retains at zero. This is an essential detail which experience 

 has confirmed, and which enables us to calculate the velocity of 

 the explosive wave in the most diverse mixtures. 



It appears that in the act of explosion a certain number of 

 gaseous molecules among those which form the inflamed sections 

 at the outset, are hurled forward with all the velocity corre- 

 sponding to the maximum temperature developed by the 

 chemical combination. Their shock determines the propagation 

 of this latter through the neighbouring sections, and the move- 

 ment is reproduced from section to section with a velocity 

 which may be compared to that of the molecules themselves. 



It is in this way that observations were made of the propaga- 

 tions of explosions, with velocities of 2480 metres per second 

 in a mixture of oxygen and hydrogen, of 2480 metres in a 

 mixture of oxygen and acetylene, and of 2195 metres in a 

 mixture of 'cyanogen and oxygen, etc. This velocity constitutes 

 a genuine specific constant for every gaseous mixture. 



The propagation of the explosive wave is a phenomenon 

 altogether distinct from ordinary combustion. It only occurs 

 when the inflamed section exercises the greatest possible 

 pressure on the adjoining section ; that is to say, when the 

 inflamed molecules preserve almost in its entirety the heat 

 developed by chemical reaction. This state constitutes the law 

 of detonation. 



