00 



Major W. T. David : Analysis of the 



After making an allowance of 30 per cent, for the absorption 

 of the quartz, the radiation registered through quartz would 

 appear to be greater than that registered through fluorite. 

 It is unlikely that this result is due to experimental error,, 

 for in the neighbourhood of the maximum temperature 

 the radiation measurements were made with a high degree 

 of accuracy. A probable explanation is that there is in this 

 epoch considerable energy in radiation of shorter wave- 

 length than 2'$ /jl for which the absorption of the quartz, 

 plate is much less than 30 per cent.* 



10. No measurements through quartz are available for 

 hydrogen and air mixtures of other strengths; but some 

 records of measurements of radiation through fluorite for 

 weaker mixtures are of interest, in that the maximum 

 gas temperatures developed approach that at w T hich it has- 

 been found that the 2*8 fju radiation disappears. The results 

 of these experiments are showm in Table VI. f The 25*4 per 



Table VI. 

 Total Radiation emitted in Explosions of Hydrogen and Aii 



Percentage 



strength of 



mixture. 



254 



mixtures of various strengths. 



Heat of 



combustion 



of hydrogen 



present in 



explosion 



vessel, 

 (calories.) 



16,320 



Max. press. 



developed. 



(lbs. per 



sq. in. abs.) 



106 



Max. temp, 

 developed. 

 (° C. abs.) 



2400 



Total radiation 

 emitted during 

 explosion and 

 subsequent 

 cooling, 

 (calories per 



sq. cm. of 



wall surface.) 



0-60 



Total radiations 



emitted 



expressed as 



percentage 



of heat of 



combustion 



of hydrogen. 



16-1 



15-0 

 10-0 



9,650 

 6,430 



70 

 59 



1500 

 1230 



0-22 

 0T2 



100 



* The energy in the luminous radiation from a coal-gas and air 

 mixture developing a maximum temperature of the same order is 

 small (see Phil. Trans. A. vol. ccxi. p. 389), though in the hydrogen 

 and air mixture it may be appreciably greater, for the combustion 

 in this mixture is much more violent. Perhaps, too, internal vibrations 

 of the nitrogen molecules corresponding to radiation of wave-length in 

 the neighbourhood of 1 n are excited. Nitrogen in a vacuum tube gives 

 a strong emission band whose maximum is at 1 jx approximately (see 

 Coblentz, ' Investigations of Infra-red Spectra,' p. 317). 



t The figures for the 10 per cent, mixture have been calculated from 

 a record giving the emission from a cone of small solid angle of the 

 gaseous mixture which is proportional to the total radiation measured 



