1911-12.] Absorption of Light by Inorganic Salts. No. VI. 61 
authorities who are of opinion that before a hydrate can be deposited from 
a solution it must be present to some extent in that solution. 
The change in colour on heating the solution is mainly to be ascribed to 
the increase of the anhydrous phase at the expense of the polyhydrate. 
This discussion of the phases in solution is interesting in connection 
with the hydrate theory emphasised by Jones (Carnegie Institution of 
Washington, Publication No. 60). 
The law of mass action has not been applied to this colour change before. 
And in the meantime I do not consider the result quite certain, as one 
assumption made, viz. that there is no compound formed by the chloride 
and the alcohol, has yet to be tested by the use of other solvents. This 
work will be commenced immediately. 
This investigation was carried out at the instigation of Dr R. A. Houstoun, 
to whom I am greatly indebted for advice and various suggestions received 
during its progress. 
{Issued separately March 20 , 1912 .) 
