190 DISCUSSION OF EVIDENCE. 



the solvate had an effect on the absorption of light, and this could be 

 explained only as due to a combination between the solvent and the 

 resonator, or something containing the resonator. 



14. The work of Jones and Strong on absorption spectra established 

 the existence of a larger number of "solvent " bands. They showed that 

 these were formed by many salts and in many solvents. They could 

 even distinguish between the bands of a salt in a given alcohol and in 

 its isomer. This was regarded as very important. The temperature 

 work of Jones and Strong was strong evidence for the solvate theory. 



15. The work of Jones and Guy on the effect of high temperature on 

 the absorption spectra of aqueous solutions, and also on the effect of dilu- 

 tion, led to results which were all in keeping with the solvate theory. 



The most important spectroscopic work of Jones and Guy, which 

 bears on the solvate theory of solution, is that in which the radio- 

 micrometer was used. It was here shown that solutions of certain 

 strongly-hydrated non-absorbing salts are more transparent than pure 

 water having a depth equal to that of the water in the solution. In the 

 case of non-hydrated salts the solution was the more opaque. This 

 shows that water in combination with the dissolved substance water 

 of hydration has less absorption than pure, free water. This is 

 regarded as striking evidence that some of the water in the presence 

 of salts which are shown by other methods to hydrate is different 

 from pure, free, uncombined water ; and the simplest explanation seems 

 to be that this is the combined water, or the water of hydration. 



16. The work of Jones and Guy was repeated and extended by 

 Jones, Shaeffer, and Paulus. They obtained results of the same general 

 character as those found by Jones and Guy. Solutions of hydrated 

 salts were in general more transparent than pure water, especially at 

 the centers of the absorption bands. Solutions of non-hydrated or 

 only slightly hydrated salts are more opaque than pure water, especially 

 at the centers of the bands. 



The above sixteen lines of evidence all point to the general correct- 

 ness of the view that when a salt is dissolved in a solvent there is more 

 or less combination between the salt, or the ions resulting from it, 

 and the solvent. The magnitude of this solvation depends upon the 

 nature of the substance and of the solvent. 



HOW THE PRESENT SOLVATE THEORY OF SOLUTION DIFFERS FROM THE OLDER 



HYDRATE THEORY. 



The present solvate theory of solution is not simply one of several 

 possible suggestions which accounts for a certain class of experimental 

 facts. It is the only suggestion that has thus far been made which 

 seems to account satisfactorily for all of the facts established. Most 

 of the above sixteen lines of evidence bearing on solvation in solution 

 were obtained as the direct result of experimental work suggested by 

 the solvate theory and carried out to test this theory. Many of the 



