174 DISCUSSION OF EVIDENCE. 



and ethyl alcohols. These facts are just what would be expected if 

 this absorption was due to simpler solvates, since the power to form 

 solvates is greater for water than for either of the alcohols, and greater for 

 methyl than for ethyl alcohol. For equal concentrations the solvates 

 would decrease in complexity as we pass from water to methyl alcohol. 

 Further, increase in dilution would change the complexity of the sol- 

 vates more in aqueous solutions than in solutions in either of the alcohols. 

 The above conclusion is, then, in perfect accord with all of the facts. 



The absorption of copper salts in the red narrows when the product 

 of concentration and depth of absorbing layer is kept constant, but 

 widens when the molecules are kept constant. Its intensity varies 

 far more with change in concentration than with change in solvent. 

 This absorption must be due to the atom, and is affected comparatively 

 slightly by the surroundings of the atom. The copper absorption in 

 the red is, then, less affected by solvates than the absorption by copper 

 in the ultra-violet. The feature of the work of Jones and Anderson, 

 which bears most directly on the solvate theory of solution, came out 

 as the result of studying the absorption spectra of solutions of salts 

 of neodymium and praseodymium, and especially of neodymium. 



Neodymium chloride was found to have quite different absorption 

 in water from what it had in methyl alcohol. This made it desirable 

 to study the absorption spectrum of this salt in mixtures of methyl 

 alcohol and water. By changing the composition of the mixtures of 

 the two solvents, we could see how the spectra corresponding to the 

 two solvents would change. 



It was found that when the proper mixture of alcohol and water 

 was used, the two spectra (the one corresponding to the alcoholic 

 solution and the other to the aqueous solution) coexisted on the plate. 

 When the amount of water in the mixed solvents increased, the "water 

 spectrum" came out more strongly; when the amount of alcohol 

 present was increased, the "alcohol spectrum" came out more strongly. 

 When the amount of water present exceeds 15 or 20 per cent, we have 

 only the "water spectrum." As the amount of water is still further 

 decreased by the addition of more alcohol, the spectrum consists of 

 the "water spectrum" and the "alcohol spectrum" superposed. As 

 the amount of water is diminished below 15 per cent, the intensity of 

 the water spectrum becomes less and less and the intensity of the 

 alcohol spectrum greater and greater. 



A question of importance in the present connection is this : Does the 

 "water spectrum" gradually change over into the alcohol spectrum" 

 as the amount of alcohol present is increased, or do we have here two 

 separate and distinct spectra, the one corresponding to the aqueous 

 solution, and the other to the alcoholic? 



To test this point, we worked with fairly dilute solutions of neody- 

 mium chloride in water, in methyl alcohol, and in mixtures of water 



