384 Proceedings of Royal Society of Edinburgh. [july 18 , 
That is to say, the heats of solution of any metallic chloride and 
bromide vary inversely as the difference between the excess of the 
heat of combination of the metallic chloride over the heat of com- 
bination of hydrogen chloride in water, and the excess of the heat 
of combination of the metallic bromide over the heat of combination 
of the hydrogen bromide in water, 
make this plain : — 
The following examples will 
Heat of Combination. 
Heat of Solution. 
[Ca,Cl 2 ] =169820 
17410 
- [H 2 ,Cl 2 ,Aq] = 78630 
91190 
[Ca,Br 2 ] = 140850 
24510 
- [H 2 , Br 2 Aq] 56760 
84090 
Difference + 7100 
Difference - 7100 
[Sr, Cl 2 ] = 184550 
11140 
- rii 2 ,Cl 2 ,Aq] 78630 
105920 
[Sr,Br 2 ] 157700 
16110 
- [H 2 ,Br 2 , Aq] 56760 
100940 
Difference + 4980 
- 4970 
[Ba,Cl 2 ] 194740 
2070 
- [H 2 ,Cl 2 Aq] 78630 
116110 
[BaBr 2 ] 169960 
4980 
- [H 2 ,Br 2 ,Aq] 56760 
113200 
Difference + 2910 
Difference - 2910 
We again see from these results how intimately heat of solution 
is related to heat of chemical combination. Whenever an element 
develops less energy in combination with bromine than with 
chlorine relatively to the hydrogen compounds of these same nega- 
tive elements, the energy is not lost ; it immediately appears in the 
heat of solution. It is worthy of note also how regularly the differ- 
ence increases by about 2000 units as we pass from the barium to 
the strontium and calcium salts. 
