'94 ' Major W. T. David : Analysis of the 



to the 4*4 /z. radiation would he greater in the weak mixtures 

 during explosion and in the neighbourhood of the maximum 

 temperature than in the strong mixtures, for the rate of 

 transfer of energy from the '2'8 [i type of vibrations relatively 

 to that from the 4*4 fju type is slower at the weak mixture 

 temperatures (particularly during the explosion period) than 

 at the strong mixture temperatures. A comparison of the 

 ratios in column 6 of Table III. with those of column 6 of 

 Tables I. and II. shows, however, that this ratio is less in 

 the weak mixture (even during the explosion period, when the 

 temperatures are much lower) than in the strong mixtures. 

 Again, in the weakest hydrogen mixture in which the 

 maximum mean temperature developed is only 1230° 0. abs. 

 — at which temperature partitioning is slow — the radiation 

 emitted is small, indicating that the energy given to its 

 vibratory degrees of freedom is small *. 



Summary of Results and Conclusions. 



19. Experimental Results. 



(i.) In explosions of coal-gas and air and of hydrogen and 

 air the ratio of the energy in the 2'8 /u radiation emitted to 

 that in the radiation of longer wave-length decreases as the 

 temperature decreases. 



(ii.) In the neighbourhood of 1200° C. abs. the emission 

 of radiation of wave-length 2*8 /jl decreases yqyj rapidly with 

 the temperature, and at 1000° C. abs. it is negligible. 



(iii.) Radiation of longer wave-length than 2°8 /x con- 

 tinues to be emitted even after the temperature has fallen to 

 900° C. abs., though at this temperature the emission is small. 



(iv.) The ratio of the energy in the 2*8 /a radiation to that 

 in the 4*4 fjb radiation in coal-gas and air mixture appears to 

 depend to some extent upon mixture strength as well as upon 

 temperature. 



* It should be pointed out that although strong 1 hydrogen mixtures 

 undergo very violent combustion (the 25*4 per cent, mixture had an 

 explosive period of only 0*017 sec.) the weaker mixtures undergo 

 comparatively gentle combustion. The 15 per cent, mixture in the 

 experimental vessel had an explosive period of 0065 sec. and the 

 10 per cent, mixture an explosive period of 0*23 sec. 



The emission of radiation in the 10 per cent, mixture during the ex- 

 plosion period ia so small that it is doubtful whether the 2*8 \i vibrations 

 are excited to any appreciable extent. The bulk of the radiation is 

 emitted during the subsequent cooling of the mixture, when the 

 temperatures are of course below 1230° O. abs. It is thought distinctly 

 probable that the radiation emitted is mainly of longer wave-length, 

 but as no record through quartz is available this cannot be confirmed. 



