870 



Intra- Molecular Energy during Combustion. 



vigorously to excite, in addition, the vibrations corresponding 

 to the shorter wave-length radiation which is transmitted by 

 quartz. 



Fig. 1. 



2000 



O -0 0-05 0-1 0-15 0-2 0-25 0= 



Time (measured from moment when pressure 

 beqlns to risej-5ec. 



Later stages of the explosion period. — In the later stages of 

 the explosion period, combustion proceeds more vigorously 

 (as is indicated by the rate of rise of pressure or gas 

 temperature— see curve P, fig. 1), and in strong mixtures it 

 proceeds, of course, more vigorously than in weak mixtures. 

 The ratio of the radiation transmitted through quartz to that 

 transmitted through fluorite in this epoch is about 55 for a 

 15-per-cent, mixture, 0*52 for a 12'5-per-cent. mixture, and 

 0'46 for a 10-per-cent. mixture *. These results go to show 

 that the more vigorously combustion proceeds, the greater 

 the proportion of short wave-length (infra-red) radiation 

 emitted, and therefore the greater the proportion of energy 

 acquired during this period by the vibratory degrees of 

 freedom corresponding to the short wave-length radiation 

 relatively to that acquired by those degrees corresponding to 

 radiation of greater wave-length. 



* Phil. Mag. Jan. 4920, p. 86. 



