Mr. Graham on the Heat disengaged in Combinations. 343 
of a solid hydrate of sulphate of soda containing ten atomis of 
water; it is remarkable how little it exceeds the heat disen- 
gaged in the crystallization of the same salt, or the fall ob- 
served on the solution of the crystallized salt. It appears as 
if water abandoned little more than its heat of fluidity on com- 
bining with dry sulphate of soda to form a solid hydrate. 
Sulphate of soda, which had been allowed to effloresce in 
dry air between 50° and 55° Fahr. for a week, consisted of 
dry salt 100 and water 0°46. ‘The equivalent quantity of this 
salt, which is so nearly anhydrous, or 44°81 grains, was dis- 
solved in 1000 grains of water with a very slight change of 
temperature, namely a rise of 0°05. 
6. Sulphate of Ammonia.—Of the hydrated salt crystallized 
by spontaneous evaporation in air, which contains one atom of 
water of crystallization, the equivalent quantity, 47°03 grains, 
was dissolved in 1000 grains of water with a fall of tempera- 
ture in three experiments of 065, 0°64 and 0°61, of which 
the mean is 0°63. 
Fall on solution of NH,O,8SO0,+ HO. 0°63. 
The salt was obtained anhydrous by drying at 248° Fahr.; 
it was granular and crystalline, and neutral to test paper. 
The equivalent quantity, 41°41, produced a fall in three ex- 
periments of 0°51, 0°53 and 0°49; of which the mean is 
O51. 
Fall on solution of NH,O,SO; . . . 0%51. 
A sensible but very small reduction of temperature, not exe 
ceeding 0°02, occurred on mixing the solution of sulphate of 
ammonia with an equal bulk of water at the same temperature, 
Dissolved in the diluted acid, consisting of a mixture of 300 
water-grain measures of sulphuric acid of density 1-1 and 700 
gtains of water, the equivalent, 41°41 grains, of the anhydrous 
salt produced a fall of temperature in two experiments of 1°17 
and 1°14; of which the mean is 1%16. Hence the fall is 
greater on the solution of the sulphate of ammonia in dilute 
sulphuric acid than in water, by 0°65. The fall of sulphate 
of soda was also greater by nearly the same amount, 0°60, 
and of sulphate of potash by 0°-53, when these salts were dis« 
solved in the same dilute acid instead of water. 
IV. Double Sulphates. 
1. Bisulphate of Potash.—Of the usual double sulphate of 
water and potash crystallized in rhombohedral crystals, an 
equivalent quantity, 85°23 grains, was dissolved in 1000 grains 
of water, with a fall in two experiments of 1°96 and 1%95, 
The same salt was fused by heat and pounded ; it dissolved 
