Radiation emitted in Gaseous Explosions. 75 



10. In considering these formulae it is suggestive to regard 

 Q as being proportional to the density of distribution of 

 chemical energy in the inflammable mixture and 6 as being 

 proportional to the rate of conversion of chemical energy 

 into thermal energy. In a previous paper it has been sug~ 

 gested that the chemical energy in process of conversion first 

 passes (either wholly or a considerable proportion of it) into 

 the form of internal vibrations of the combining molecules, 

 and it is reasonable to suppose that the radiation to which these 

 vibrations give rise and which comes from the whole mass of 

 the burning gas should be a maximum towards the end of the 

 period during which combustion proceeds at its maximum 

 rate. 



(b) Cylindrical Explosion Vessel I cm. diameter 

 and I cm. long. 



11. It will be realized that the radiation values in the pre- 

 ceding sections have referred to explosions in a single vessel 

 30 cm. in diameter and 30 cm. long. Some indication of the 

 effect of size of vessel on the radiation values may, however,., 

 be obtained from the writer's experiments on the diathermancy 

 of coal-gas and air mixtures exploded in a vessel with silver- 

 plated walls which could be made reflecting by polishing or 

 absorbent as regards radiation received by them by coating 

 with a thin layer of dull black paint *. 



12. In fig. -i an attempt is made to plot R tmax . (which is 

 proportional to K max .) for mixtures of various densities for a 

 cylindrical vessel I cm. diameter and I cm. long against L 

 Confine the attention first to the thick curve which con- 

 nects Rimax. with I for a 15 per cent, mixture at atmospheric 

 density. The -value for Z = 30 (viz. 6'6 calories per sq. cm., 

 per sec.) is, of course, directly obtained from the experiments, 

 for the cylindrical vessel used in these experiments was of 

 dimensions 30 cm. by 30 cm. It is clear, too, that 1^ = for 

 1 = 0, so that there are two definite points on the curve. Two 

 other points, one for 1 = 15 and the other for Z — 59, may be 

 roughly fixed in the light of the following considerations. 

 That for 1 = 59 will certainly lie somewhere between R; max . 

 for 59 cm. in the polished vessel (which is 10'9) and 

 Rtmax. for 59 cm. in the blackened vessel (which is 8*4) 



* Phil. Trans. A. vol. ccxi. p. 395. 



