Mr. Graham on the Heat disengaged in Combinations. 345 
of agreement among the results. Taking the mean of the re- 
sults,— 
Fall on solution of HO, SO,+ NaO,SO; . 0°98. 
The fall of temperature observed on dissolving bisulphate 
of potash in water approaches that observed on dissolving the 
neutral sulphate of potash in dilute sulphuric acid, the first 
being 1°95 and the second 2°-04. But it is doubtful if the 
fall in the second case can be ascribed simply to the imme- 
diate formation and solution of bisulphate of potash, when the 
sulphate of potash and dilute sulphuric acid are mixed and 
dissolved together. In the formation of bisulphate of potash 
we have both the substitution of sulphate of potash for the 
second atom of water of the sulphate of water, and the throw- 
ing off of all the remaining water combined with the sulphate 
of water in hydrated sulphuric acid, bisulphate of potash con- 
taining no water of crystallization. Now asa great deal of 
heat was disengaged by this additional water on originally 
combining with the sulphate of water, we should expect heat 
again to be assumed by that water on becoming free, or cold 
to be produced. 
3. Sulphate of Magnesia and Potash.—An equivalent quan- 
tity of the crystallized salt, namely 126-28 grains, containing 
33°75 grains of water of crystallization, was dissolved in 976°2 
grains of water at 52° Fahr., with nearly two minutes’ stir- 
ring; a fall of temperature was observed of 2°30 R. The 
experiment was repeated with the same result. But a slow 
rise of temperature was afterwards observed to occur in the 
solution, independent of any external influence, which in the 
course of four minutes amounted to 0°20 R. This is not 
the only salt in which the fall of temperature on solution is 
immediately followed by a slight but sensible rise. 
This salt was made anhydrous by a low red heat to which 
it was exposed for upwards of two hours, but was not fused. 
When the salt was thrown into water after this ignition, it 
gave a liquor which remained white and milky for two or three 
minutes, but the salt finally dissolved without residue. The 
rise of temperature on the solution of a whole equivalent of 
the anhydrous salt, or 92+53 grains, was 1°57; on solution 
of one-half of an equivalent, or 46°2 grains, 0°80 ; which gives 
1°60 for the whole equivalent. 
Rise on solution of Mg O,SO,+ KO,SO,. . . 1°60 
Fall on solution of Mg O, S O;+ KO,SO,+6HO 2°30 
Whole heat disengaged by Mg O, SO, + K O, S O, 3°90 
The crystallized sulphate of magnesia and potash, dried by 
anitre-bath, was found to retain 18°32 water to 100 anhy- 
Phil. Mag. S. 3. Vol. 22. No.146. May 1843. 2A 
