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



ignition temperature. The fact that this has not been fully 

 taken into account previously seems to account in some 

 measure for the differences in the results obtained by other 

 workers. It was further shown that the period of slow 

 combustion before explosion took place also depends on the 

 properties of the combustible substance, and a theory was 

 briefly developed connecting the "delays" observed at 

 different temperatures with the effect of a rise in temperature 

 on the rate of combustion, i. e. with the so-called tempera- 

 ture coefficient of the reaction. The object of the experi- 

 ments described in this paper was to test these theories 

 quantitatively, and to attempt to deduce from the results the 

 temperature coefficients in certain typical cases. The mea- 

 surement of the temperature coefficients of simple gaseous 

 reactions is of considerable importance in connexion with 

 the theory of chemical reactions,, for one of the great 

 difficulties in the development of theory hitherto has been 

 the fact that most gaseous' reactions have to be investigated 

 under conditions which are complicated by the disturbing 

 influence of solid catalysts or of the walls of the containing 

 vessel. Gaseous reactions which occur on sudden com- 

 pression are free from this complication, for the walls of the 

 containing vessel are much lower in temperature than the 

 gas; by quantitative measurements of the rate of loss of 

 heat near the ignition temperature, and of the delay before 

 explosion occurs, it therefore seems possible to gain some 

 real insight into the mechanism of homogeneous gas reactions. 

 Experiments of this nature also have a considerable practical 

 interest for the development of internal combustion engines, 

 for, according to our views, the tendency of a fuel to 

 detonate at high temperatures depends not only on its 

 ignition temperature but also on the temperature coefficient 

 of its reaction with oxygen. 



Previous experiments on the ignition of gases by sudden 

 compression have been made by Talk, at Nernst's suggestion 

 (J. Amer. Chem. Soc. xviii. p. 1517 (1906), xxix. p. 1536 

 (1907)), and by Dixon and his co-workers (see Dixon, Brad- 

 shaw & Campbell, Journ. Chem. Soc. 1914, p. 2027 ; and 

 Dixon & Crofts, p. 2036). Nernst first put forward the view 

 that at the ignition temperature the evolution of heat due to 

 the reaction was just greater than that lost to the sur- 

 roundings; but this suggestion has not hitherto been carried 

 further, since no previous workers have attempted to 

 measure the rate of loss of heat near the ignition tempera- 

 ture. Further, previous work has been mainly confined to 

 the measurement of ignition temperatures of mixtures of 



