Chemical Constitution of Saline Solutions. 257 



In order to be able to judge from absorption spectra of the condition of a 

 salt when dissolved in water, and of any cliemical change taking place when 

 the solution is heated, it is necessary to know the answers to the following 

 questions : — 



1st. How far do the absorption spectra of aqueous solutions of various salts of 

 the same metal differ from one another, and how are salts affected by different 

 solvents ? 



2nd. What change in the absorption of light is caused by heating coloured 

 solutions to 100° C? 



3rd. Is there any remarkable difference between the spectra of hot and cold 

 solutions which corresponds to the difference between the crystallized salts at the 

 ordinary temperature and when dehydrated at 100° C. ? 



