ISOMERIC CHANGE 215 



constitute the electrodes in the chemical, if not perhaps in 

 the electrical, sense. When the interaction takes place at a 

 high temperature it appears that this solid circuit may be dis- 

 pensed with, although in practice it is found that its place is 

 frequently supplied by the (glass) walls of the containing vessel, 

 which exert a remarkable influence in promoting action between 

 gases. 



The recent experiments of Dixon, 1 which have shown that an 

 explosive wave can be propagated through a gaseous mixture 

 with a velocity equal to that of sound, have an important bearing 

 on this point, since it is clear that under these conditions the 

 influence of surface-contact has been eliminated. It is not 

 difficult to form a picture of what happens in such a case. The 

 amount of water present is usually small, but here and there 

 a circuit may be formed of which the essential elements are, 

 for instance, 



H., 

 H, 



OH, 

 OR, 



2 or R, 



OH 



Cl„ 



the water being assumed to be sufficiently impure to conduct 

 the current. At ordinary temperatures the circuit is unable 

 to discharge, owing to the high electrical resistance of the 

 gaseous " electrodes " ; at a red heat this resistance is so far 

 reduced that electrolysis takes place and the circuit assumes 

 the form — 



HO 

 HO 



H.,0 „ n 

 H - Q or H,0 



HC1 

 HC1 



When the gas is detonated the pressure wave has the effect of 

 momentarily raising the temperature of the gas as it passes 

 through ; as a consequence each of the electrolytic circuits is 

 discharged, and the catalyst is released for further action. If 

 the electrolysis be accompanied by the liberation of a sufficient 

 quantity of heat, the catalyst finds itself in contact with other 

 gaseous molecules under conditions favourable to immediate 

 interaction, so that in a very short time the wave of detonation 

 is followed by the complete combustion of the gas. If, however, 

 the energy liberated by the electrolysis be small, or be wasted 

 in raising the temperature of a diluting gas, the catalyst is only 

 able to form a circuit with molecules which are too " cold " to 

 discharge, and the explosion dies out. 



1 Phil. Trans. 1903, 200, 315-52. 



