382 Proceedings of Royal Society of Edinburgh, [july 15 , 
to positive values through, zero when the salts are insoluble. As in 
soluble salts the heat of neutralisation is practically constant, it 
follows that the heats of solution vary with the relative variations of 
[M,X 2 ] and [M,0,Aq] involving definite chemical actions. We 
should expect, therefore, that the heats of solution would vary in 
a periodic manner with the nature of the elements, as with other 
chemical phenomena. The following diagram, representing the heat 
of solution of the chlorides, although defective in many places from 
want of data, seems distinctly to show that this is so, and that solu- 
tion is a periodic function of the weights of the elements. 
