Radiation from Hot Gases. 263 



Curve B' is the differential o£ curve B, and shows the rate 

 at which the gaseous mixture emits radiation at various times 

 after ignition in calories per sq. cm. of wall surface per sec. 



Fig. 2. 



* • S 5 ,^ 



ks? N ** <0 



1600 -8 



1200 -6 



800 -4- 



400 -2 

















~9-8/o MIXTURE OF 

 Co/U.GflS&AlFi. 















^p 





















B 





si 











1 » 



/ v 



/ 

 / 

 / 





>' 





|-0 5 §h 









/ ' 









"--**.. 



1 °£ £ S 

 * $ Q 



yg 1 













•3 -4- -5 -6 



Time after Ignition -sec. 



-a 



It will be noticed that the emission is a maximum sometime 

 during explosion, just before the gas temperature attains its 

 maximum value. During this time chemical combustion is 

 rapidly proceeding, and this must be to a very large extent 

 responsible for the intensity of the emission at this point. 

 It cannot be due wholly to temperature, for the emission is 

 less at the moment of maximum gas temperature than at 

 this point, and Prof. Hopkinson has shown that every part 

 of the gaseous mixture has a higher temperature at the 

 moment of maximum temperature than at any other time *. 

 It is possible that the violence of combustion causes a con- 

 siderable part of the energy of combination to pass into the 

 form of intra-molecular vibrations. Part of the energy in 

 these vibrations is lost by radiation, but the greater part is 

 converted into the two other kinds of molecular energy — 

 rotational energy and translational or pressure energy. 



During the cooling of the gaseous mixture the emission is 

 still very considerable, at any rate until the gas temperature 

 has fallen to 1000° C. abs., and it seems highly probable that 

 the emission during this time is mainly thermal in origin (i.e. 

 that the molecular vibrations are for the most part excited 

 during molecular collisions). It is difficult to believe that 

 this large emission is wholly due to continued combustion 

 (or after burning). Mr. Dugald Clerk's experiments seem 



* Roy # Soc, Proc, A. vol. lxxvii. p. 889. 



