DISCUSSION OF EVIDENCE. 175 



and methyl alcohol. The object in using dilute solutions was to be 

 able to study the structure of the bands in the different solvents. In 

 the more dilute solutions the several parts of any given band would 

 come out clearly and could be measured. The result was to show 

 that the "alcohol spectrum" was quite different from the "water 

 spectrum." It had different components and they were arranged in 

 a different way within the bands. 



In mixed solvents, then, the two spectra coexisted, and we did not 

 have the one passing over into the other as we changed the composi- 

 tion of the mixture of alcohol and water. The "water" spectrum and 

 "methyl alcohol" spectrum had equal intensities when the mixture of 

 the water and methyl alcohol contained from 6 to 8 per cent of water. 



Neodymium nitrate shows change in the spectra analogous to those 

 manifested by the chloride, when dissolved in mixtures of water and 

 one of the non-aqueous solvents. The change with the nitrate is not 

 so striking as with the chloride. 



Praseodymium chloride in mixtures of water and methyl alcohol 

 shows the same general features as were manifested by the chloride 

 of neodymium. In the case of praseodymium chloride there is this 

 additional feature: in the alcoholic solution an entirely new band 

 appears, having no analogue in the aqueous solutions. This new band 

 in the ultra-violet is by far the most intense in the entire spectrum 

 of praseodymium chloride. On adding water to the alcoholic solution 

 this band entirely disappears. In this case the alcohol spectrum is 

 quite different from the water spectrum. 



These results show beyond question that the solvent plays an impor- 

 tant role in the absorption of light by solutions. The question arises, 

 what is this role? It is difficult, not to say impossible, to explain the 

 action of the solvent on any other ground than that a part of the solvent 

 combines with the ions and molecules of the dissolved substance, and 

 the solvated parts have different resonance from the unsolvated. This 

 means that they would absorb different wave-lengths of light. The 

 alcoholates would have different resonance from the hydrates, whence 

 the different absorption spectrum in alcohol from that in water. 



We regard this evidence in favor of solvation in solution as important, 

 and, as we shall see, many examples of "solvent" bands were brought 

 to light in the investigation which followed. 



WORK OF JONES AND STRONG. 



The work of Jones and Anderson was continued by Jones and 

 Strong. 1 They investigated a number of problems, including the effect 

 of the solvent on the absorption of light by the dissolved substance. 

 Jones and Anderson, as we have just seen, had found one good example 



Carnegie Inst. Wash. Pubs. Nos. 130 and 160. Amer. Chim. Journ.,43, 37, 224 (1910); 45, 1 

 (1910) ; 47, 27 (1912). Phys. Zeit. 10, 499 (1909). Phil. Mag., April, 1910. Journ. Chim. Phys., 

 8, 131 (1910). 



