L62 
PROFESSOR H. B. DIXON ON THE RATE OP EXPLOSION IN GASES. 
2505 metres per second as the mean of four double determinations. The rate of the 
sound-wave ‘‘ S,” calculated on the hypothesis that the mixture burns directly to 
carbonic oxide and hydrogen, is 2330. The calculated velocity is, therefore, about 
7 per cent, too low. This is the only instance 1 have yet found where the observed 
rate is largely in excess of the calculated sound-wave. On the other hand, the rate 
of explosion of acetylene and an equal volume of oxygen was found to be 2961 metres 
per second as the mean of four double determinations. The rate of the sound-wave, 
calculated on the hypothesis that the mixture burns directly to carbonic oxide and 
hydrogen, is 3084. The calculated velocity is, therefore, about 4 per cent, too high. 
This difference between the explosion of ethylene and acetylene, with an equal 
volume of oxygen, is somewhat striking ; it seems to point to some different mode of 
decomposition in the two cases. 
As stated by Dalton, a mixture of marsh gas with half its volume of oxygen will 
not explode ; but a mixture of equal volumes of marsh gas and oxygen explodes. I 
have determined the rate of explosion of this mixture, and find the velocity is 
2 ^ per cent, faster than the sound-wave calculated for the reaction— 
CH^ + O 3 = CO + H 3 + H 3 O. 
Table XLIII.—Rate of Explosion of Marsh Gas with an equal volume of Oxygen. 
Mixture. 
CH, + 0., 
Berthelot’s 0 ... . 
2184 
Rate of explosion 
2528 
V 
2466 
At the temperature produced in this reaction the steam must be partly dissociated 
—lowering the rate. The observed velocity, therefore, is undoubtedly too high to 
reconcile with the calculated sound-wave. Marsh gas must, therefore, be classed 
with ethylene as giving exceptionally high rates. 
At this point a difficulty must be pointed out which I have hitherto avoided. I 
have endeavoured to show that the explosion-wave is in part propagated by the 
movements of the yet unburnt molecules. The question arises—Are these unburnt 
molecules ever broken up by impact before they are burnt ? In the case of an endo¬ 
thermic compound, such as cyanogen or acetylene, is the propagation of the flame 
partly due to the explosive decomposition of the compound, previous to the combus¬ 
tion of its constituents ? If so, the unburnt gas would be diminished in density, and 
one might expect to find the explosion of endothermic compounds travelling at 
