﻿100 Messrs. H. T. Tizard and D. R. Pye on the 



gaseous mixtures with air were compressed in a non-turbulent 

 condition, while in the second a high-speed fan was kept 

 running throughout the period of compression and subsequent 

 ignition. The use of the fan increased the rate of heat-loss 

 at the compression temperature by about three times ; hence 

 the difference in ignition temperatures observed with and 

 without the fan running gives an important and necessary 

 check on the value of the temperature coefficient which is 

 calculated from the " delay " curve obtained when the non- 

 turbulent gases are compressed. The temperatures given 

 below represent the average temperature of the gas at the 

 instant of maximum compression. By measuring the com- 

 pression pressures in each experiment, a value of ei 7," the 

 apparent ratio of the specific heats, is obtained from the 

 expression : 



V 



•*- max. V 



where r is the compression ratio. 



The average value of 7 is taken for the series, and the 

 compression temperatures then calculated for each case from 

 the expression 



T 



y— 1 







In each set of experiments the initial mixture of gases was 

 of the same composition throughout, the proportion of air 

 being somewhat greater than that required for complete 

 combustion. The intention of using a weak mixture was to 

 avoid as far as possible the deposition of carbon ; as stated 

 above, the absolute ignition temperature is not affected 

 appreciably by fairly wide changes in the original strength 

 of the mixture. 



IX. The first results with heptane gave a very satisfactory 

 confirmation of the theory developed above. The results of 

 the experiments are given in the following tables and 

 diagrams, which include measurements from all the records 

 made under each set of conditions. No unsatisfactory 

 records have been discarded. 



