1913] on The Spectroscope in Organic Chemistry 71;^) 



of flour, which could easily be obtained in the minute quantity 

 re(]uired for this purpose. Inspection of the photographs shows that 

 the spectra are very similar. There cannot, therefore, be any doubt 

 that the colouring matter of flour, if not identical with, is closely 

 allied to carrotene. 



The underlying causes of the relations between chemical structure 

 and absorption spectra have been the subject of much speculation. 

 Hartley considers that the phenomena of absorption are intimately 

 connected with the vibration of the atoms ^vithin the molecule. 

 This view has much to recommend it, but oljviously its application is 

 limited by the present imperfect state of our knowledge of the 

 internal mechanism of the molecule. A theory has been advanced 

 according to which a1)sorption bands are only exhibited 1 »y compounds 

 whose molecules are in a state of change or flux. In the case of ben- 

 zene, for example, the old idea is i-evived that the carbon atoms are 

 linked together by alternate double and single bonds, which are 

 perpetually changing positions. The presence of the bands in the 

 spectrum of benzene, is supposed to be in some way connected with 

 these changes. Substances, however, are known which have banded 

 spectra in regard to which such an explanation is inadmissible. 



Quite recently a promising attempt has l)een made to bring the 

 production of banded spectra into relation with the theory of electrons. 



It must be confessed, however, that no satisfactory explanation 

 of the phenomena of aljsorption has yet been formulated, and that 

 the theoretical development of the subject lags behind its practical 

 application. 



[J. J. D.] 



3 B -2 



