TJie Rate of Explosions in Gases. 139 



Marsh Gas. Ethylene. Cyanogen. 

 Rates found 94 92 84 



The results are, therefore, in favour of the view that in the 

 explosion of these gases, the carbon is first burnt to carbonic 

 oxide. 



But it might be objected that the increase in rate found 

 on diminishing the oxygen is due, as in the case of electrolytic 

 gas with excess of hydrogen, to the lower density of the 

 mixture. Taking the most favourable case — that of marsh 

 gas — the density of the mixture is lowered 4 per cent by 

 diminishing the oxygen from O4 to O3. Now, if the rate 

 varies inversely as the square root of the density this would 

 only increase the rate 2 per cent. So that even if the heat 

 of the chemical reaction remained the same in the two cases, 

 the observed increase in rate could not be accounted for by 

 the diminution in density. I need not point out that in 

 the case of cyanogen the diminution of oxygen is accom- 

 panied by an increase in density. 



But stronger evidence is obtained by comparing the 

 explosion rate of these gases (i) when fired with oxygen 

 sufficient to burn the carbon in them to carbonic acid, and 

 (2) when nitrogen is substituted for the oxygen in excess of 

 that required to burn the carbon to carbonic oxide. We 

 have seen that oxygen added to electrolytic gas hinders the 

 explosion more than nitrogen. In precisely the same way 

 oxygen added to a mixture of equal volumes of cyanogen 

 and oxygen hinders the explosion more than the same 

 volume of nitrogen. The conclusion we must come to is 

 that the oxygen added to the mixture expressed by the 

 formula C2N2 + O2 is as inert (so far as the propagation of 

 the explosion-wave is concerned) as oxygen added to the 

 mixture expressed by the formula H2 + O. The same 

 phenomena occur in the explosion of marsh gas, ethylene, 

 and acetylene. 



K 



