GENERAL SUMMARY OF RESULTS. 91 



The curve for aluminium sulphate brings out this new feature; at 1/jl the 

 solution is more transparent than the water. Beyond 1.04/t the water is 

 transparent to 1.1 7/jl, beyond which the solution is the more transparent, as 

 with magnesium and calcium chlorides. 



In the region 1.2/z water is the more opaque when a shallower layer of solu- 

 tion is used. From 1.29/j. to 1.36/*, water is the more transparent; beyond 

 1.38/1 the solution is the more transparent. 



The explanation of these remarkable results is that they must be due to 

 some action of the dissolved substance on the solvent. That the solvent 

 can affect the absorption spectra of the solution was first shown by Jones and 

 Anderson; 1 and a large number of examples of this same action has since 

 been found by Jones and Strong. 2 The action was satisfactorily explained 

 as due to a combination of the solvent with the dissolved substance, and this 

 explanation accounted for many facts which could not be otherwise satis- 

 factorily explained. This theory of solvation in solution has aided us in 

 explaining many phenomena which the theory of electrolytic dissociation 

 alone could not account for, as has frequently been pointed out. 



The same solvate theory of solution seems to aid us in explaining the facts 

 just discussed. Those substances that do not form hydrates when in the 

 presence of water show normal results as far as absorption spectra are con- 

 cerned. Their solutions have the same absorption as so much pure water, 

 the substance itself showing no absorption. 



It is the hydrated salts, and only these, which give the abnormal results 

 herein recorded. The combined water seems to have less poiver to absorb light 

 than free or uncombined water. This would account for all of the facts 

 observed. 



It should be noted that the presence of the salt shifts the absorption of the 

 water towards the longer wave-lengths. It was earlier observed that rise in 

 temperature and increase in concentration shifted the absorption of the salt 

 towards the longer wave-lengths. The effect of rise in temperature and of 

 increase in concentration is to simplify the hydrates existing in the solution. 

 This simplified resonator shifts the absorption towards the red. The effect 

 of the salt on the absorption of the water is the same as rise in temperature 

 and increase in the concentration of the solution on the absorption of the 

 dissolved substance. It may be that the dissolved substance diminishes the 

 association of the solvent and thus simplifies the resonator. This may be 

 true especially with the water of hydration or the water combined with the 

 dissolved substance. 



This new line of spectroscopic evidence bearing on the solvate theory of 

 solution is regarded as probably the most direct that we have or can hope to 

 obtain in favor of the view that there is combination between solvent and 

 solute. 



In studying the absorption spectra of salts, the intensity of the light after 

 passing through the solution of the salt in question, was compared with the 



1 Cam. Inst. Wash. Pub. 110. 2 Ibid., 13) and 160. 



