﻿116 Messrs. IL T. Tizard and D. R. Pye on the 



Table XVIII. 





Heptane 

 C 7 H 16 . 



Ether 

 C 2 H 5 .O.C 2 H 5 . 



Carbon 

 bisulphide 



cs 2 . 



Composition of gas by weight... 1 : 20 of air. 



i 



1:15 



1:8 



T =igni(ion temperature " 280° 0. 



212° 0. 



253° C. 



c v at ignition temperature ' 0'20 0'20 



0-18 



Rate of evolution of beat due to; 25 calories . ~ 

 reaction per gram of mixture per second. [ 



18-5 



Total beat of combustion pei 



1 510 calories. 510 calories. 



386 calories. 





Value of b/T 



■ io-o+5 % ! n-o+5°/_ 



6-7 ±10% 









XIX. In order to calculate the true temperature co- 

 efficient B (see equation 5) from the values of b/T , it is 

 necessary to examine the significance of T a little more 

 closely. As already stated, T is a measure of the lowest 

 average temperature of the gas at which ignition takes 

 place. Now the actual temperature of the gas after sudden 

 compression can hardly be uniform throughout ; in fact, 

 when the gas ignites after a considerable delay, it is always 

 found that the pressure, and therefore the average temper- 

 ature, falls, in some cases quite considerably, before ignition 

 takes place throughout the mass. This shows clearly that 

 that portion of the gas which ignites at first has initially 

 a higher temperature than the average, thus confirming 

 Dixon's experiments. Absence of information as to the 

 temperature gradients which may exist under these conditions 

 has no doubt led Nernst and Dixon in their experiments to 

 calculate the ignition temperature as if the compression were 

 adiabatic, and to ignore the influence of loss of heat during 

 compression and before ignition. They assume, in fact, that 

 that portion of the gas which does ignite is at the adiabatic 

 temperature. 



It is hardly likely, however, that big differences in 

 temperature exist after compression when the gases are in a 

 turbulent state ; and the fact that the temperature coefficients, 

 calculated from the differences in "average" ignition 

 temperature between turbulent and non-turbulent mixture, 



