782 
Proceedings of the Boyal Society 
Now, the reason of this is perfectly obvious. It is due to the 
laws of solution. Any variation from the above differences on the 
heats of formation of the anhydrous salt is at once counterbalanced 
by the heat of solution, which varies inversely. The following 
example will make this evident : — 
Salt. 
Heat of Formation. 
Heat of Solution. 
Total. 
[H, Cl] 
22000 
17315 
39315 
[H,Br] 
8440 
19940 
28380 
Difference, 
13560 
-2625 
10935 
[Na,Cl] 
97690 
-1180 
96510 
[Na,Br] 
85770 
- 190 
85580 
11920 
990 
10930 
and so on in other cases. 
In my last paper I pointed out that the differences in the heats 
of formation of HC1, HBr, and HI are exactly proportioned in- 
versely to the differences of the atomic weights of Cl, Br, and I. 
On further consideration, I am convinced the law obtains in all 
compounds of these elements, and the different proportion found in 
solutions is due to the modifying action of the affinity of these 
elements for the 0 of the water, and in the case of solid compounds 
to another cause. This, however, with many other points, I leave 
for further consideration. 
Note to Paper on Laws of Solution. 
There is another way of putting the matter, which not only con- 
firms the foregoing laws, but also shows the conditions which deter- 
mine the heats of solution whether positive or negative. The heats 
of solution are simply balances of transactions between the elements 
of the body dissolved and the elements of the solvent. The follow- 
ing examples will illustrate this : — 
