﻿Ignition of Gases by Sudden Compression. 119 



practically independent of the concentration of the com- 

 bustible substance. If the rate of the reaction were deter- 

 mined solely by the amount of oxygen present, we might 

 expect the temperature coefficient also to depend solely on 

 the oxygen, and therefore to be the same in all cases. This 

 is clearly not true. Nor does the temperature coefficient, in 

 the case of the heptane explosion which has been most closely 

 investigated, correspond at all closely to that calculated by 

 means of equation (12) from the infra-red absorption of 

 oxygen. Oxygen has an absorption band corresponding to 



\ = &2fi, or j/ = '94x10 14 ; hence, since \ =4*86 x 10" 11 , 

 we should have * 



B = 4550 (calc.) instead of 13,200 + 9 per cent. (obs.). 

 It is clear that equation (12) cannot be applied. On the 

 other hand, if the rate of reaction depended on the product 

 of the number of active molecules, both of oxygen and the 

 other reactant, we should expect, on the same theory, to 

 find the temperature coefficient given by 



B = yO'i + 'a), 



where v u v 2 correspond to absorption bands in the reacting 

 substances. 



Now, all hydrocarbons have a weak absorption band at 

 \ = 24 /x, and a fairly strong one at 3*43 /jl. Taking 

 \ = 2*4 fi, which is most favourable to the theory, we have 

 v 2 = 1-25 x 10 14 and Vl (oxygen) ='94 x 10 14 . 



Hence B = 4-86 x 10" 11 x 2'2 x 10 14 = 10,700. 



This approaches more closely the experimental value 

 B = 13,200 ±9 percent. 

 It must be pointed out, however, that this approximate 

 agreement is only obtained by an assumption as to the actual 

 mechanism of the reaction which does not agree with the 

 existing experimental results. 



The failure of the " radiation theory " to account for the 

 results obtained in these experiments is more significant 

 when we regard it in a different way. The theory requires 

 that the rate of a chemical reaction should be proportional 

 to the density in the reacting system of the radiation which 

 is absorbed by the reacting substances. Now, in the case 

 of gases which are caused to react by a rise in temperature 

 due to sudden compression, the radiation density must 

 remain practically unchanged, for the temperature of the 

 walls remains constant. It may be momentarily increased 



