346 Mr. Graham on the Heat disengaged in Combinations. 
drous salt. Now 18:24 water represents 3 H O; the crystal- 
lized salt has consequently lost one-half of its water, retaining 
only three atoms. Of this salt, an equivalent quantity, or 
109°4 grains, were dissolved in 1000 grains of water, with a 
fall in three experiments of 1°35, 1°30 and 1°35, of which 
the mean is 1°33. 
Fall on solution of Mg O, SO,+KO,SO;4+3HO 1°38. 
The fall on the solution of this hydrate is less than on the 
solution of the former, by the heat disengaged in the combi- 
nation of the salt with the deficient three atoms of water. The 
heat disengaged by the union of the salt with the first three 
atoms of water comes therefore to be 2°93, and with the second 
three atoms of water 0°97, making together 3°-90. Hence 
as nearly as possible three times as much heat are disengaged 
by the first three atoms of water as by the last three atoms. 
4. Sulphate of Magnesia and Ammonia.—The solution of 
an equivalent quantity, 113°13 grains, of the crystallized salt 
in 1000 grains of water was attended by a fall of temperature, 
in two experiments, of 2°20 and 2°:15, of which the mean is 
2°17. If dissolved in 976°2 grains of water, like the potash 
salt, the fall would have been about th more, or 2°24. 
Fall on solution of MgO, SO,+NH,0,S0,+6HO 2°24, 
The fall on the solution of the corresponding potash salt 
was 2°30. 
5. Protosulphate of Iron and Ammonia.—The solution of 
122'17 grains, the equivalent quantity of the crystallized salt 
in 1000 grains of water, was attended with the same fall of 
2°-20 in two experiments. But this determination should be 
increased by ;},th, like the last; the fall then becomes 2°27. 
Fall on solution of FeO, SO,+KO,S0O,+6HO . 2°27. 
6. Sulphate of Manganese and Ammonia.—In two experi- 
ments 61°20 grains of the crystallized salt, being one half of 
the equivalent quantity, were dissolved in 983 grains of water 
with a fall of 1°11 and 1°13; or 2°24 for a whole equivalent. 
Fall on solution of MnO, SO,+ NH,0, SO,+6HO. 2°24, 
It thus appears that the heat of liquefaction of the four 
crystallized double salts, sulphate of magnesia and potash, 
sulphate of magnesia and ammonia, sulphate of iron and 
potash, and sulphate of manganese and ammonia, is sensibly 
the same. 
7. Sulphate of Zinc and Potash.—The fall on the solution of 
half an equivalent, 69°26 grains, of the crystallized salt in 
1000 grains of water, was in three experiments 1°33, 1°27 
and 1°30, of which the mean is 1°30. The fall for a whole 
equivalent, 138°52 grains, is therefore 2°60. 
