330 Mr. Graham on the Heat disengaged in Combinations. 
sorption of a certain quantity of heat or fall of temperature, 
namely by a fall of 0°-66 in the hydrated sulphate of copper, 
0°93 in the hydrated sulphate of zinc, and 0°83 in the hy- 
drated sulphate of magnesia. The last quantities being added 
to the heat first observed in the solution of the oxides, and 
the preceding quantities being subtracted from the same heat 
first observed, we obtain as the corrected determinations of 
the heat evolved from the combination with sulphuric acid 
of the oxides enumerated (or rather from the substitution of 
these metallic oxides for the basic water of the sulphate of 
water), by oxide of copper 1°°37, by oxide of zinc 2°21, by 
magnesia 8°°41 ; quantities which, so far from being equal, are 
nearly in the ratio of the numbers 2, 3, and 12. It is ob- 
vious, therefore, that experiments to determine both the heat 
absorbed in the solution of salts, and that evolved in their 
hydration, must precede inquiries respecting the heat disen- 
gaged in the formation of the salis themselves by the combi- 
nation of their essential constituents, when the salts are 
formed in the humid way. 
The apparatus employed consisted of a delicate therimo- 
meter of small bulb, namely, that used in the wet-bulb hy- 
grometer, as prepared by Greiner of Berlin. Every degree 
was divided into five parts, each part again was divisible by 
the eye into five parts, so that observations were made to sth 
of a degree. The degree is that of Reaumur’s seale. After 
trying glass jars and various other vessels, it was foutid that 
nothing answered better than a large platinum crucible, 
which weighed 1201'9 grains, and was capable of containing 
5 ounces of water. The thermometer and crucible, with a 
hollow cylinder of palladium, weighing 207°6 grains, employed 
as a stirrer, were all the apparatus necessary. Of the salt or 
other substance experimented upon, a quantity corresponding 
with its atomic weight, and representing a single equivalent, 
was always used; and the quantity of water was constant, 
namely 1000 grains, and relatively large, so as to render the 
change of the specific heat of the fluid insensible. 
The water, crucible, stirrer and thermometer, beitig the 
same in all the experiments, the results are strictly compa- 
rable. The numbers express the relative quantities of heat 
disengaged from atomic equivalents of the bodies. 
I. Hydration of Oil of Vitriol. 
1. HO,SO. The protohydrate of sulphuric acid em- 
ployed was pure, and of density 1°848. The quantity used 
of this and other substances was always one-twentieth of the 
number expressing the equivalent taken in grains; that is 30°68 
