﻿Ignition of Gases by Sudden Compression. 99 



Table II. 

 Values of a( ° \t for different values of r . r and . 



T/T . 



6/T =12. 



= 10. 



=8. 



=6. 



= 4. 



1004 



•086 



•112 



•155 



•233 



•418 



101 



•056 



•075 



•108 



•169 



•321 



103 



•0245 



•036 



•056 



•098 



•209 



107 



•0081 



•014 



•025 



•051 



•131 



1-11 



•0033 



•0065 



•0135 



•032 



•095 



1-27 



•0002 



•0007 I 



1 



•0022 



•0083 1 



•0415 



The curves bring out clearly the effect of the two main 

 factors which determine the characteristics of an explosion 

 by sudden compression ; namely, the initial rate of loss of 

 heat, and the temperature coefficient. If two gases have the 

 same ignition temperature under the same conditions of loss 

 of heat, the sharpest explosion will occur in the case of the 

 gas with the. highest temperature coefficient, and the greater 

 in this case will be the effect, on the magnitude of the delay 

 before explosion, of: a higher temperature of compression. 

 On the other hand, in any one case, the ignition temperature 

 will be raised by carrying out the experiment under con- 

 ditions which involve an increased rate of loss of heat ; at the 

 same time the sharpness of the explosion will also be in- 

 creased. 



VIII. To test the above theory, and to use it to obtain a 

 measure of the temperature coefficient in certain cases, we 

 chose three substances : heptane C 7 H 16 , ether C 2 H 5 .O.C 2 H 5 , 

 and carbon bisulphide CJS 2 . These substances were chosen 

 for the following reasons : (a) they could be obtained in a 

 sufficiently pure state ; (b) they all have low ignition tem- 

 peratures, which lessens the practical difficulties of the 

 experiments ; (<•) they are known to behave very differently 

 from the point of view of detonation when used as fuels for 

 internal combustion engines; and (d) their difference in 

 chemical and physical properties makes the comparison of 

 their behaviour on combustion particularly interesting. To 

 test the theory adequately we considered it absolutely 

 necessary, particularly in view of the simplifying assump- 

 tions made, not to be content with one set of conditions for 

 the ignition experiments. Two series of experiments were 

 therefore made with each substance; in the first series the 



H2 



