24 Prof. E. C. C. Baly on 



phase to a less condensed phase, an amount of energy is 

 required for «ach molecule which is equal to a small whole 

 number o£ quanta at the infra-red fundamental. If this 

 energy is supplied at the phase frequency, then the one 

 quantum is far larger than is required, and the excess 

 beyond that necessary is radiated again at the infra-red 

 fundamental. Since the molecules can absorb energy at the 

 infra-red fundamental, part or whole of this radiated energy 

 will be re-absorbed by fresh molecules, with the result that 

 they are activated. A number of molecules, therefore, will 

 react after the absorption of one single quantum of energy 

 at the phase frequency, the number depending on the 

 proportional amount of the radiated energy that is re-absorbed 

 by the system. Unless, therefore, the conditions are such 

 that the whole of the radiated energy escapes from the 

 system, the Einstein law cannot hold for absorption at the 

 phase frequency. 



In the reaction proper energy is again evolved, since 

 the reacting molecules are endowed with increased energy 

 content as a result of the first stage. It is a matter of 

 indifference whether this energy is radiated in frequencies 

 characteristic of the reacting molecules or of the resulting 

 molecules, since both are built up from the same atoms. 

 The energy radiated during the reaction of the molecules 

 can therefore be absorbed by fresh molecules which become 

 activated. If any of this energy is re-absorbed by the 

 system, then the divergence from the Einstein law, already 

 established in the first stage, will still further be increased 

 in the second stage. 



A specific instance may be taken to illustrate the above, 

 and that of the photochemical decomposition of hydrogen 

 peroxide may be chosen. According to the observations 

 of Henri and Wurmser *, made with a dilute aqueous 

 solution, 180 molecules were decomposed for every quantum 

 of energy absorbed at the phase frequency, which is approxi- 

 mately 1*3 x 10 15 . As pointed out by these authors, this and 

 other analogous results form as they stand a very damaging 

 criticism of Einstein's law. Now, in all probability the 

 infra-red fundamental of hydrogen peroxide is very near to 

 that of water (4*9 x 10 13 ), and therefore the phase frequency 

 may be taken as 26" times the infra-red fundamental. It 

 may be assumed simply for purposes of calculation that the 

 frequency of the reactive phase of hydrogen peroxide is 



25 times the infra-red fundamental. If so, a molecule of 

 hydrogen peroxide absorbs one quantum at the molecular 



* Compt. Rend. clvi. p. 1012 (1913). 



