PROPAGATION OF EXPLOSIVE WAVE. Ill 



explosive wave through the tubes. Here is found the same 

 resistance to combustion that is characteristic of the compounds 

 formed with nitric oxide (p. 63), a resistance that only dis- 

 appears in compounds that are capable of developing an 

 excessive temperature. In short, in the experiments described 

 above, we did not observe any rate of propagation of the wave 

 below 1000 metres per second. 



Moreover, the propagation of the wave ceased whenever the 

 theoretical temperature, T, of the compounds formed with free 

 oxygen fell below 2000 (for hydrogen or cyanogen associated 

 with nitrogen) or 1700 (for carbonic oxide or methane asso- 

 ciated with nitrogen) ; figures corresponding to a lower limit of 

 the energy of the molecules. 



Finally, the propagation of the wave ceased every time the 

 volume of the products of combustion amounted to less than 

 the quarter (for hydrogen and nitrogen) or even the third (for 

 methane or cyanogen associated with nitrogen) of the total 

 volume of the final compound. 



6. Taking all these observations into consideration, the pro- 

 pagation of the explosive wave is quite a distinct phenomenon 

 from ordinary combustion. It only occurs when the layer 

 ignited exercises the greatest possible pressure upon the next 

 layer, i.e. when the ignited gaseous molecules possess the 

 maximum velocity and consequently the maximum translating 

 energy ; which is simply the mechanical expression of the fact 

 that they preserve almost the whole of the heat developed by 

 the chemical reaction. This is shown by the approximate 

 agreement of the calculations based upon the theoretical 

 estimate of the translating energy with the values obtained by 

 experiment for the velocity of the explosive wave. It is also 

 shown by the correlative increase of the pressure and velocities 

 towards the point of ignition. 



7. The first coincidence shows, moreover, that dissociation 

 has little influence in these phenomena ; perhaps because it is 

 restrained by the high pressure developed along the path of the 

 wave and by its short duration. If this were not the case, the 

 energy, and consequently the velocity, would fall far below 

 the value calculated. 



The influence of dissociation seems also annulled by the fact 

 that the velocity of the wave is independent of the initial 

 pressure (without admitting that dissociation is independent of 

 the pressure). 



8. It may, however, be remarked in conclusion, that it is the 

 undulatory movement which is propagated, and not the gaseous 

 mass which is transported with such great velocities. In fact, 

 the velocity of the wave is the same, as has been shown, in a 

 tube open at both ends, closed at one end and open at the other, 

 or even closed at both ends. 



