234 HYDRATES IN AQUEOUS SOLUTION. 



solutions. These bands, however, undergo the well-known shift in posi- 

 tion, due to a change in the dielectric constant of the medium produced 

 by the presence of more and more of the dehydrating agent. It is at least 

 very doubtful whether we would have the same ionic complexes in the 

 non-aqueous solutions as in the solutions in water as the solvent. 



Having pointed out the most serious defects in the various theories that 

 have been proposed to account for such color changes as have been dealt 

 with in this section, we shall now show how all the facts recorded in the 

 preceding pages seem to confirm the hydrate theory in the form originated 

 and emphasized by Jones. 



Since the relations between the selective absorption of light and the exist- 

 ence of hydrates may not be obvious, a brief discussion of this matter will 

 now be given. Of course, in the present stage of our knowledge of the nature 

 of solutions, it is not possible to form a detailed mechanical conception of the 

 various processes that came into play in solutions when arbitrary changes 

 are made in concentration, in the temperature, in the solvent, etc. Never- 

 theless, the general view which we hold may be explained as follows: In 

 the first place the phenomenon of absorption is primarily one of resonance, 

 and since light waves are electromagnetic waves, it follows that the absorbing 

 system must be electrical in its nature. The energy of a vibration of a given 

 period will be absorbed to the greatest extent by a system whose natural 

 period of vibration is most nearly equal to that of the first vibration, and it 

 may not be absorbed at all by a system whose period differs appreciably 

 from that of the incident waves. In this way the selective phase of the 

 phenomenon of absorption is explained. It is almost superfluous to state 

 that the resonator of which we are conceiving may be very complex, and 

 may have any finite number of discrete periods of vibration. Exactly how 

 this resonator is related to the ion of electrolysis, as this term is usually 

 understood, can not be decided at present. Nor is this relationship a matter 

 of fundamental importance to the question of the existence or non-exist- 

 ence of hydrates. It seems natural to suppose that the vibrations of this 

 resonator would be strongly influenced by the nature of the medium sur- 

 rounding it, not only by virtue of changes in the viscosity, specific inductive 

 capacity, etc., of the medium, but also by the condensation around it or 

 near it of complexes of water molecules. The way in which these com- 

 plexes or hydrates might affect the absorption of the resonator is as follows: 

 The vibration of a given period of the resonator might be so greatly damped, 

 either directly or indirectly, by the hydrate, that its amplitude would fall 

 below the value which marks the limit of our experimental means of detect- 

 ing absorption. 



If this were the case we should not be aware of the existence of the absorp- 

 tion, and we should therefore say that no absorption of the given period takes 



