520 Prof. E. C. C. Baly on 



shows two ultra-violet band groups and one fluorescence 

 maximum, all three o£ which are much nearer to the red 

 than those in neutral solution. There exist differences 

 between the wave-numbers of all these six bands which are 

 all multiples of 160. It follows from this that the ultra- 

 violet band groups must possess central wave-numbers which 

 are multiples of 1 60. 



Now Purvis * has measured the wave-lengths of the 

 absorption lines composing one of the ultra-violet band groups 

 of phenol, and they lie between the limits A,= 2812 and 2500 

 tenth-metres. The only even multiple of 160 which lies 

 near the centre of this band is 3840, which = 160 X 24 f. The 

 wave-numbers of the absorption lines therefore maybe calcu- 

 lated from 3840±?ix2'5, 3840±rcx3*7, and 3840±wx4«0; 

 and the values obtained when corrected for the refractive 

 index of air show very good agreement with those measured 

 by Purvis. Two of the basis constants of benzene were used 

 and one of those of water, because phenol is undoubtedly an 

 aromatic compound, that is to say its benzenoid properties 

 are far more pronounced than those of a derivative of water. 



In Table III. are shown the results for the first few lines 

 on both sides of the central line together with Purvis's 

 observations. It is somewhat remarkable that the calculated 

 wave-lengths of the absorption lines over the whole band 

 group themselves together, and that Purvis has observed in 

 most cases those lines which mark the heads of these groups. 



Owing to the fact that the infra-red spectrum of phenol 

 has only partially been investigated, it is not possible to 

 adduce any collateral evidence, as was done in the case of 

 benzene, as regards the coicindence between the frequencies 

 of the principal lines in the absorption band with those 

 calculated from the infra-red bands. The number of lines 

 calculated is so large that the agreement between these and 

 the observed values might be criticised as being no better 

 than the theory of probability would give. It must, however, 

 be remembered that the additive principle is clearly estab- 

 lished as far as the infra-red spectrum of phenol is concerned. 



Many other examples might be given in support of this 

 principle, but it is only in a very few that the theory can 

 be tested upon the ultra-violet absorption band group, since 



* Trans. Chem. Soc. ciii. p. 1088 (1913). 



t The even multiple of 160 is taken because the frequency-difference 

 between the two absorption bands of pbenol in neutral or alkaline solution 

 is 2x160. 



