Mr. Graham on the Heat disengaged in Combinations. 333 
It will be observed that the heat evolved by the first atom is 
sensibly the same as that evolved by the four following atoms, 
the quantities being 1°47 and 1°52; the difference between 
these numbers being within the limits of errors of observation. 
The same conclusion is drawn from his experiments on the 
hydration of oil of vitriol by Professor Hess. Supposing the 
whole heat disengaged in the hydration of sulphate of water 
to be divided into 23 parts, 9 are evolved by the first atom of 
water, 9 by the next four atoms, 1 by the following two atoms, 
and 4 by the remaining excess. 
Although the experiments detailed above agree with those 
of M. Hess in bringing out one curious result, they yet differ 
from them to an extent which it is difficult to account for 
in other respects. Thus reducing my results to the same 
scale as those of M. Hess, the comparison is as follows. In 
the hydration of the sulphate of water, 
Hess. Graham. 
Heat from the first atom of water. . . 2 2: 
ive second atom of water. . 1 0°72 
ig next three atoms of water 1 1°35 
33 additional excess of water 1 1:18 
5 5°25 
8. HO, SO, HO+ 10HO. An equivalent quantity of 
this hydrate, or 92°55 grains, was mixed with 969°3 grains of 
water, the quantity of the latter being diminished so as to 
make up 1000 grains with the water already in the acid hy- 
drate. ‘The rise of temperature in two experiments was 0°37 
and 0°41, of which the mean is 0°°39. This hydrate contains 
four atoms more of water than the last operated upon, and 
disengages 0°29 less heat. The heat, therefore, due to the 
combination of the additional four atoms of water is 0°29. 
9. HO,SO, HO+ 14H O. Of this hydrate the equi- 
valent, or 115°05 grains, was mixed with 915°6 grains of 
water, and occasioned a rise of temperature in two experi- 
ments of 0°°23 and 0°20, of which the last was believed to be 
the most trustworthy result. Hence the four atoms of water 
last added evolve 0°-09, or about one-third of the quantity 
evolved by the preceding four atoms of water. 
10. HO, SO, HO+ 24 HO. The equivalent of this 
hydrate, or 171°3 grains, was mixed with 859°4 grains of 
water, and produced in one experiment a rise of 0°15. The 
hydrate was kept for three days before it was diluted in the 
experiment; for immediately after its preparation the heat 
which this hydrate yielded on dilution was considerably less 
than the quantity assigned above to it; indeed not more than 
0°06 in one experiment. 
