332 Mr. Graham on the Heat disengaged in Combinations. 
is therefore the heat evolved by the addition of the second 
atom of water to the sulphate of water. It is scarcely one- 
third of 1°47, the quantity evolved by the first atom. 
4. HO,SO,;+3HO. With 47:55 grains, or one equi- 
valent of this hydrate, the rise by dilution was in three expe- 
riments 1°31, 1°31 and 1°27, of which the mean is 1°°30. 
The difference between the heat evolved by this and the pre- 
ceding hydrate is 0°*56, which is therefore the heat evolved by 
the addition of the third atom of water to the sulphate of water. 
Now the second atom evolved 0°°53, so that the second and 
the third atoms of water appear to evolve sensibly the same 
quantity of heat. This curious result favours the conclusion, 
that the second and third atoms of water go together; or 
that the hydration of the sulphate of water here advances by 
two atoms at a time, and that no intermediate hydrate exists, 
in a state of solution at least, between H O, SO,+ HO 
and HO,SO,;+3HO. The last may be represented as 
HO,SO, HO+2H0O. 
5. HO,SO,;+4HO. With 53°18 grains, or one equi- 
valent of this hydrate, the rise of temperature on dilution was 
1°05, 19°07 and 1°05; mean 1°06. The difference between 
this and the preceding hydrate, namely 0°24, is therefore the 
heat evolved by the combination of the fourth atom of water 
with sulphate of water. 
6. HO,SO,;+5HO. With 58°8 grains, or one equi- 
valent of this hydr ate, the rise of temperature on dilution was 
0°°88, 0°88 and 0°85; mean 0° 87. The heat from the com- 
bination of the fifth atom of water is 0°19. It is not impos- 
sible that the heat evolved from the fifth is the same in quan- 
tity as that evolved from the fourth atom of water, and that 
these two atoms go together like the second and third. The 
present hydrate of sulphate of water corresponds with crystal- 
lized sulphate of copper. 
7. HO,SO;+7HO. With 70°05 grains, or one equiva- 
lent, the rise was 0°68, 0°71 and 0°65; mean 0°68. The 
difference between the effect of this and the preceding hydrate 
is 0°°19, which is therefore the heat evolved by the combina- 
tion of the last two atoms of water, namely the sixth and 
seventh atoms. This hydrate of sulphate of water corre- 
sponds with crystallized sulphate of magnesia. 
By the continued hydration of the sulphate of water, the 
quantities of heat evolved are therefore as follows :— 
Heat evolved. noe formed, 
By first atom of water ........ 1°47 ,50O,; + HO. 
By second and third atoms together . 1° 09 . is - 0; SO; +3HO. 
By fourth and fifth atoms together .. 0°43 ... HO,SO,; + 5HO. 
By sixth and seventh atoms together. 0°19 ... HO,SO,; +7HO. 
By an additional excess of water... 0°68 ... HO,SO; +7HO-+aHO, 
