﻿732 Prof. H. C Jones on Absorption Spectra- 



hut might be produced by simple hydrates formed by the 

 breaking down of more complex hydrates with rise in 

 temperature. 



Cobalt salts show marked absorption in the red, only when 

 yery concentrated, at elevated temperatures, or in the presence 

 of a dehydrating agent. The absence of red absorption at 

 moderate concentration shows that this absorption is not due 

 to ions. The conditions for the absorption in the red suggest 

 that it might be due to molecular aggregates. This, however, 

 is debarred by the fact that the red absorption increases with 

 rise in temperature, while this would break down any such 

 aggregates. We would, then, most naturally conclude that 

 the absorption in the red was due to simple hydrates, since 

 the conditions favouring this absorption favour the existence 

 of such hydrates. 



In a similar manner it was shown that the ultra-violet 

 absorption of copper salts was connected with the solvation 

 of the molecules — the absorption being smaller the more 

 complex the solvate. 



Direct spectroscopic evidence for the existence of solvates 

 was furnished by Jones and Anderson in their study of salts 

 of neodymiura. A salt like neodymium chloride was found 

 to have a very different absorption spectrum in water from 

 what it had in methyl alcohol. Neodymium chloride in the 

 proper mixture of water and methyl alcohol shows both the 

 " water" bands and the * c alcohol ' bands. By varying the 

 amounts of the solvents relative to one another, the relative 

 intensities of the two sets of bands can be changed at 

 will. 



Neodymium nitrate in a mixture of water and methyl 

 alcohol shows bands of the same character in the two solvents 

 as the chloride. 



Praseodymium chloride in a mixture of water and methyl 

 alcohol shows the same kind of change as neodymium chloride. 

 In this case an entirely new band appears in the alcohol, which 

 has no analogue in the aqueous solution. 



The existence of " water " bands and " alcohol " bands in 

 the aqueous and alcoholic solutions, respectively, is interpreted 

 by Jones and Anderson as direct evidence for the existence 

 of hydrates in the aqueous solutions, and alcoholates in the 

 alcohol solutions — in a word, is direct spectroscopic evidence 

 for the solvate theory. 



The largest amount and most direct spectroscopic evidence 

 for the solvate theory of solution has been brought to light 

 by the work of Jones and Strong, which has been in progress 

 continuously during the past three years, and the results are 



