336 Mr. Graham on the Heat disengaged in Combinations. 
the results were for sulphate of magnesia 0°°85, 0°80 and 
0°83, of which the mean is 0°°83 ; for sulphate of zine 0°97, 
0°91, 0°:92, of which the mean is 0°93: greater cold occa- 
sioned by the solution of sulphate of zinc than of sulphate of 
magnesia, by the first experiments 0°08, by the last experi- 
ments 0°10. 
Of sulphate of zinc, carefully dried and made perfectly an- 
hydrous, the equivalent quantity, 50°22 grains, was dissolved 
in 1000 grains of water, with the exception of a mere trace of 
flaky matter. The rise in one experiment was 4°20; in 
another 4°15; mean 4°17, The results then are,— 
Rise on solutionof ZnO,SO, . . . . 4°17 
Fall on solution of ZnO,SO,+ 7HO . 1°00 
Whole heat disengaged by ZnO, SO, . . 5°17 
There is the same difficulty in obtaining the protohydrate of 
sulphate of zinc exactly definite, as the corresponding hydrate 
of sulphate of magnesia. ‘The hydrate operated upon con- 
tained to 100 sulphate of zinc 11°99 water, instead of 11°207, 
which is a single equivalent. ‘The equivalent quantity, 56°21 
grains, was dissolved in 1000 grains of water, and occasioned 
a rise of temperature in two experiments of 2°34 and 2°33. 
As the rise for the anhydrous salt was 4°°17, the deficiency 
from the hydrate, 4°17 — 2°34 = 1°83, is due to the quantity 
of water already combined in the salt of the experiment. But 
this deficiency cannot be entirely ascribed to a single atom of 
water, as the combined water exceeded that proportion as 
11-99 to 11°21. It is difficult to find proper elements for the 
necessary correction, but we may probably reduce the amount 
of deficient heat to 1°71, that is, as 11°99 to 11°21, without 
any considerable error. Hence 
Rise on solution of ZnO, SO, HO . . 2°45 
Fall on solution of Zn O,SO,+7HO . 1°00 
Whole heat disengaged by ZnO,SO,, HO 3°45 
The difference between the heat disengaged by the protohy- 
drate and the anhydrous salt, or the heat due to the combi- 
nation of the first atom of water, namely 1°71, is almost 
exactly one-third of the whole heat disengaged in the hydra- 
tion of sulphate of zinc; one-third of 5°17 being 1°72. The 
quantities of heat disengaged by sulphate of zinc in the two 
conditions specified, are therefore as 4 to 6. 
3. Sulphate of Copper.—The equivalent quantity of the 
ordinary crystallized salt, containing 5 HO, namely 77:97 
grains, was dissolved in 1000 grains of water, with a fall of 
temperature in three experiments of 0°67, 0°'65 and 0°68, 
of which the mean is 0°67. This and other more sparingly 
