NATURE OF SOLUTION. 617 
the case of those solutions which allowed the formation of chlorine hydrate ; for 
water was thus retained in the flask while a stronger solution was drawn off, 
so that the solution became weaker than it was originally, after the chlorine 
hydrate was decomposed. It is proposed to determine the solubilities of such 
solutions at a later date, without previous formation of hydrate, so that the 
second part of the curves may be strictly comparable. The principal object in 
the present research has been to determine the first part of each curve, and fix 
the maximum points. 
. The salts which prevent the formation of ape hydrate are chlorides of 
magnesium, calcium, iron, cobalt, and strontium (almost entirely). 
On referring to the curves it will be found that those for these salts form a 
well-defined group, having the following characteristics :— 
1. The maximum point is at a temperature lower than that for water by 
from 10 to 15 degrees. 
2. The tops of the curves are flat, and the descent is very gradual. 
_ The occurrence of maxima in the case of these salts is not to be explained 
in the same way as in cases where solid chlorine hydrate appears. In seeking 
for an explanation it is to be noticed that all of these chlorides have a strong 
attraction for water, and tend to form definite hydrates. The anhydrous 
chlorides unite with water very readily, forming definite crystalline hydrates 
stable at higher temperatures than have been employed in this research. 
It may be supposed that two forces come into play to determine the amount 
of chlorine in the solution—(1) the solubility of chlorine in the ‘ free” water, 
and (2) the attraction of calcium chloride for water, determining the amount 
of “free” water. It is a case where chemical combination is a function of the 
temperature. As the temperature falls the amount of free water decreases, 
but at the same time its coefficient of absorption increases, and at a quicker 
rate than the decrease of free water. Therefore, on the whole, the solubility 
increases as the temperature falls. But as the temperature continues to fall 
the rate at which the chloride goes on attaching the water increases, until it 
overtakes the rate of increase of solubility, and a maximum is reached. From 
this point onwards the chloride keeps and increases its ascendancy and the 
solubility decreases. The gradual rise and fall of the curves favour this theory. 
There is no sudden descent from the maximum, as in the case of those salts 
permitting the formation of the hydrate. 
The curves for the remaining solutions do not admit of classification, but 
there seems a general tendency for a strong attraction for water to coincide 
with a maximum at a low temperature, except in the case of cadmium chloride 
where the maximum appears at 10°, very near that for water. There is also to 
be remarked in the curves for those chlorides which permit the formation of 
VOL. XXX. PART III. 5 E 
