424 Prof. Baly and Mr. Tryhorn on Liglit 



solution, and it may be noted that a small change in this 

 fundamental wave-number will produce a relatively larger 

 shift in those wave-numbers which are its multiples. 

 Although we have observed that the fundamental infra-red 

 band shifts on solution by an amount and in the direction 

 comparable to that of its multiples, yet no accurate obser- 

 vations of the infra-red absorption spectra of substances in 

 solution have been published. We have examined the 

 absorption spectrum of an alcoholic solution of /3-naphthol 

 ethyl ether in the neighbourhood of 3 /x, where both solvent 

 and solute each show strong absorption bands. We found, 

 however, that the two types of molecules do not separately 

 exhibit their own absorption bands, but that the solution shows 

 only one absorption band, which moreover is not a mean 

 of the two due to the two components. The solution absorbs 

 as if it were a single entity with an absorption band of its 

 own which differs from that of each component. 



It is possible that this will explain the interesting fact 

 that the wave-length of the infra-red emission band of the 

 Bunsen flame is not the same as that of either carbon 

 monoxide or carbon dioxide. On the other hand, the two 

 oxides are in equilibrium in the flame, and it is this equi- 

 librium which is emitting the radiation. Just as a solution 

 seems to exhibit an absorption band of its own and not the 

 bands peculiar to its components, so the equilibrium of 

 carbon monoxide and carbon dioxide present in the Bunsen 

 flame emits a radiation of its own and not that of its com- 

 ponents. 



We thus arrive at a reasonable explanation of the change 

 in position of absorption bands when the absorbing substance 

 is dissolved in a solvent, namely, that the solution acts as a 

 single entity with its own fundamental frequency of vibra- 

 tion in the infra-red. Since the frequencies of the ab- 

 sorption bands in the visible and ultra-violet regions are 

 multiples of this fundamental frequency, we see that these 

 must shift in the presence of a solvent. 



As has been pointed out in the previous papers of this 

 series, one of the results of the relationship between the 

 fundamental infra-red frequency and the phosphorescent, 

 fluorescent, and absorption bands in the visible and ultra- 

 violet regions, is the existence of constant differences between 

 the wave-numbers of the latter. Since the relationship can 

 obviously only hold good when all the wave-numbers are 

 characteristic of one molecular entity, the constant differences 

 may be taken as evidence of the presence of one molecular 

 entity. The existence of the constant differences enables us 



