TRANSACTIONS OF SECTION B. 401 



Before dealing with the quantity of energy necessary for the conversion the rela- 

 tion between the characteristic vibration frequencies of a given inolecule must be 

 mentioned. It has been found that the characteris-tic frequencies of any molecule in 

 the visible and ultra-violet region are simple multiples of a fundamental frequency 

 in the short-wave infra-red region. Thus, if v be the fundamental short-wave infra- 

 red frequency, there can only be free periods of vibration at '2v, 3r, 4c, &c These 

 free periods of vibration are evidenced by absorption, fluorescence, or phosphorescence 

 band groups as the case may be. In general, in the case of a simple molecule, only 

 one absorption band group in the ultra-violet is shown, that is to say, only one of the 

 possible multiples of the fundamental short-wave infra-red frequency is active. Such 

 a molecule, therefore, can absorb radiant energy of two frequencies only between the 

 wave-length limits 5^ and 0-2^, namely, at the fundamental infra-red frequency v and 

 the ultra-violet frequency v^, where v, = j/r, y being a positive integer. According to 

 the Einstein law, if the molecule undergo a photochemical reaction, the minimum 

 quantity of energy required will be given by hv^. 



On the other hand, if the energy be absorbed at the lower frequency v, it would 

 seem that the same total quantity must be taken up in order to bring the molecule 

 to the active condition. That is to say, y quanta must be absorbed at the lower 

 frequency, since /ic, = yhv. This must be the case if the Marcelin conception hold 

 good that the critical increment of energy necessary to bring the molecule into the 

 reactive state is independent of the vibration frequency. 



This modification of Professor Lewis's theory would seem to bring it into harmony 

 with the general results of absorption spectra observations. One further deduction 

 may perhaps be made. Professor Lewis stated that in order to bring a molecule into 

 the reactive phase a whole number of energy quanta must be absorbed in the short- 

 wave infra-red region. The molecule, however, can also absorb energy at a frequency 

 which is a nn^ltiple of that infra-red frequency. There does not appear to be any 

 obvious reason why any one multiple should be active more than any other multiple 

 in the ultra-violet. It would seem possible from the foregoing to deduce an explana- 

 tion. If the total energy necessary were equal to y quanta at the infra-red frequency 

 then the active frequency in the ultra-violet would be y times the infra-red frequency, 

 that is to say, the multiple of the infra-red frequency active in the ultra-violet is 

 defined by the number of infra-red quanta which together amount to the necessary 

 energy increment. There would seem to be no dilKculty in advancing a mechanical 

 explanation of the foregoing somewhat analogous to that put forward by Bohr for 

 atomic structure. A development of this would be out of place in this discussion, 

 but the general conception has the merit of bringing Einstein's photochemical law 

 and Marcelin's and Lewis's theories into line with absorption spectra observations. 



One of the most interesting features of the phenomena of reactivity and catalysis 

 is the frequent failure of the law of mass action. It is obvious, in those cases where 

 the conversion of the inactive molecules into their active forms is brought about by 

 the action of a solvent, that if the relation between the effective masses of active and 

 inactive phases obey the law of mass action no advantage would be gained by the 

 theory. A quantitative investigation of the relation between the two has shown, 

 however, that the mass action law is not obeyed. In the simplest case, where the 

 molecule is converted into the active form by the action of a solvent, it is clear that 

 if X be the fractional part converted into the active form, ,r should be independent of 

 the concentration if the law of mass action hold good. Experiment has shown that 



X is not constant, but that a; = 1 — e " where "V is the volume of the solution and 

 a is a constant depending on the nature of solvent and solute. If A/A, be the ratio 

 between the masses of active and inactive molecules, then 



log^^=aV; 



in such case the solvent is acting as catalyst, and it would seem that the behaviour 

 of catalysts generally is susceptible of explanation on the above lines. 



An interesting point is to be noted in connection with the formula, namely, that 

 when a is very small x remains appreciably constant with changes in V when V is 

 small. In other words, the law of mass action is approximately obeyed in fairly 

 concentrated solutions. 



A short general discussion followed. 

 1915. D D 



