334 Mr. Graham on the Heat disengaged in Combinations. 
11. HO,SO,HO+s6HO,. The equivalent quantity 
of this diluted acid, or 238°S grains, was mixed within an 
hour of its preparation with 792 grains of water; the rise of 
temperature was 0°11. ; 
12. HO,SO,HO+48HO. The equivalent quantity, 
or 3068 grains, was mixed about three hours after its prepa- 
ration with 724°4 grains of water; a rise occurred of 0°08. 
The dilution of the same hydrate twenty-four hours after its 
preparation was attended with a rise of 0°13. 
The last hydrate is oil of vitriol diluted with nine times 
its weight of water, yet it was still capable of evolving a sen- 
sible quantity of heat by further dilution. The term at 
which the mixture of acid and water ceases to disengage heat 
on a further addition of water, was not observed, but the effect 
was insensible in a mixture formed of one part of the concen- 
trated acid and thirty parts of water, 
Il. Hydration of other Magnesian Sulphates, 
The heat produced in the hydration of different anhydrous 
sulphates, compared with oil of vitriol, appears in the follow- 
ing results ; equivalent quantities of the anhydrous salts in 
the solid state being thrown into the same quantity of water, 
and the rise of temperature obseryed after the hydration and 
complete solution of the salts. 
Protosulphate ofmanganese 3°22 
Sulphate of copper . . . 3°73 
Sulphate of water . , . 38°86 
Sulphate of zine. . . . 4°17 
Sulphate of magnesia . . 4°33 
The most material difference in the circumstances of the ex- 
periments is, that while the oil of vitriol was liquid, the salts 
with which it is compared were necessarily applied in the 
solid form. The liquefaction of the latter during the expe- 
riment, would therefore occasion an absorption of heat of un- 
known amount, which does not occur in the latter. 
1, Sulphate of Magnesia.—The same mode of experiment- 
ing was followed and apparatus used as in the preceding ex- 
periments with oil of vitriol. On dissolving the equivalent 
quantity, 77°35 grains (one-twentieth of 1547:02), of the cry- 
stallized salts in 960°6 grains of water, a fall occurred in three 
experiments of 0°96, 0°:90 and 0°89, of which the mean is 
0°92. In these experiments, the water contained in the cry- 
stals, which amounts to 39'4 grains, was deducted from the 
1000 grains of water usually employed to dissolve the salt; 
but if this quantity of water is supposed to be added, the 
mean result would become 0°88. 
