126 POPULAR SCIENCE MONTHLY 



ism must be closely connected with some peculiar vibration or free 

 period synchronous with the oscillation frequency of the light rays 

 absorbed. The oscillation frequency, however, is about the same for 

 all the substances just examined and lies between the limits 3,600 and 

 3,800, no matter what the labile atom may be. We are, therefore, 

 forced to the conclusion that the absorption bands can not be due 

 directly to this oscillating labile atom, or, in other words, the vibration 

 frequency of this atom is not identical with the oscillation frequency 

 of the light absorbed. This inference is strongly substantiated by 

 physical evidence which represents atomic motion as far less than that 

 of this magnitude of light rays. There remains then but one final 

 solution of this question, or the conclusion that the absorption band 

 is due directly to the change of the linking which accompanies the 

 wandering of the labile atom. In the case of the keto-enol tautomerism 

 just discussed, we may represent the change graphically as follows: 



— CH=C— CH 2 — C— 



Ah ** D 



At some stage in its transformation the hydrogen atom must have 

 wandered to the half-way point of its journey and have been linked 

 definitely to neither the carbon nor the oxygen atoms. We should then 

 have the phase in which the carbon and oxygen atoms change linking. 



— CH— C— 

 (H) 



By the examination of countless numbers of organic compounds 

 it is found that absorption bands in the ultra-violet region of the 

 spectrum are shown only by compounds exhibiting some form of 

 tautomerism, whether this be due to the keto-enolic type or to a periodic 

 type, like that present in ring compounds. The oscillation frequency 

 of the light absorbed in all cases of keto-enol tautomerism is about the 

 same, but with an increase in the mass of the molecule as brought about 

 by the displacement of one atom by a second atom or group of atoms 

 of greater relative weight, a decrease in the oscillation frequency is 

 observed. This displacement, however, is only small and does not 

 interfere with the general assumption that there is present some condi- 

 tion common to the whole group upon which the absorption directly 

 depends. 



From the standpoint of modern theories regarding the structure 

 of the molecule, there must arise in this tautomeric change a constant 

 making and breaking of the Faraday tubes of force. This means a 

 constant disturbance of the electron systems and, consequently, similar 

 vibrational disturbances in the ether. From Hewitt's studies in 

 fluorescence these electronic disturbances, due to dynamic isomerism, 



