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:
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.
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 condition 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,
