172 DISCUSSION OF EVIDENCE. 



It was found that this also produced a widening of the absorption 

 bands. This was in keeping with the effect of increasing the concen- 

 tration of the solution, which also simplified the hydrates. 



Jones and Uhler also studied the effect of adding water to solutions 

 in non-aqueous solvents. Thus, water was added to solutions in 

 methyl and ethyl alcohols, acetone, etc. The effect of adding water 

 was to narrow the absorption bands. All of these results were regarded 

 as in keeping with the solvate theory of solution. 



WORK OF JONES AND ANDERSON. 



The work of Jones and Uhler on the absorption spectra of solutions 

 was greatly extended in a number of directions by Jones and Anderson. 1 

 They worked with salts of cobalt, nickel, copper, iron, chromium, neo- 

 dymium, praseodymium, and erbium. Only that phase of the work will 

 be discussed here which bears on the solvate theory of solution. 



We will first consider the results with salts of cobalt. There is a 

 region of one-sided absorption in the ultra-violet. This band narrows 

 with dilution, but remains of approximately constant width when the 

 number of molecules in the path of the beam of light is kept constant, 

 indicating that the absorbers here are the undissociated molecules. 



The band X3300 disappears rapidly with increase in the dilution of 

 the solution, even when the number of molecules in the path of the 

 beam of light is kept constant. This band increases rapidly in intensity 

 with rise in temperature, and can be accounted for best by assuming 

 that it is due to a relatively simple hydrate. It is well known that 

 rise in temperature breaks down complex hydrates into simpler ones, 

 which would give rise to the band; and, further, increase in dilution 

 produces more and more complex hydrates. These would cause the 

 disappearance of a band due to simpler hydrates. 



The green cobalt band can not be due to the cobalt ions, since it is 

 not most intense where the number of cobalt ions is the greatest. The 

 width of this band does not vary, if the light is passed through such 

 depths of the solution that the product of the concentration multiplied 

 by the depth is kept constant. This would indicate that this band 

 is due to the cobalt atom, whether combined as in the molecule or 

 dissociated as an ion. 



The absorption in the red is characteristic of concentrated solutions 

 alone. This would show that it is not due to the cobalt ion. We 

 might suppose that it was due to aggregates of molecules; but this 

 view is not tenable, since the absorption in the red increases with rise 

 in temperature, which breaks down such aggregates. High tempera- 

 ture and great concentration favor the formation of simple hydrates 

 and also increase the absorption in the red. The red absorption can 

 therefore be accounted for as due to simple hydrates in solution. 



Carnegie Inst. Wash. Pub. No. 110; Amer. Chem. Journ., 41, 163 (1909). 



