﻿Ignition of Gases by Sudden Compression. 117 



agree so well with those calculated from measurements of 

 time of ignition at various temperatures with non-turbulent 

 mixture, confirms the views taken in the previous paper 

 (Tizard, loc. cit.) that it is unlikely also that any big 

 differences of temperature exist in the non-turbulent mixture 

 after compression. In the absence of direct evidence on 

 this point, however, it is important to calculate the " adia- 

 batic " temperatures also in the above cases. 



The mean specific heats C„ per gram molecule are : 



Heptane (room temperature-300°C.) = 50 calories 



approx. 

 Ether (65°-230° C.) = 33'6 calories (Regnault), 

 CS 2 (70°-194° O.)=10'0 (Regnault). 



Taking these values, and C y = 5'0 for air, we obtain the 

 figures for the mean true value of " y" and the corresponding 

 adiabatic temperatures, given in the following table. 



Table XIX. 



Heptane. 



Ether. 



OS 2 . 





Mean apparent value of 



" y " (observed) 



Mean true value of y ... 

 " Average" ignition teni- 



1-313 

 1-353 



553 abs. 



1-309 

 1-347 



485 abs. 



516 



31°C.=6-4°/ 



1-332 

 1-384 



526 abs. 



572 



46° 0. =8-7% 



il Adiabatic" ignition 



591 



41° C. =7-4% 







The average specific heat for CJS 2 taken in the above 

 calculations is probably too low, since it refers only to a 

 range of temperature up to 194° C, whereas the ignition 

 temperature was 260° C. 



It will be observed that the difference between the average 

 observed and the theoretical adiabatic temperatures is not 

 very great ; we consider that the "average" temperature is 

 probably closer to the true ignition temperature than is the 

 "adiabatic" temperature, but for the purpose of estimating 

 every possible source of error in the temperature coefficients, 

 it is better at this stage to recognize the uncertainty, and 

 take for the true values of the ignition temperatures the 

 values 



Heptane 573° absolute 



Ether 500° „ V ±4 per cent. 



CS 9 549° „ 



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