Mr, Graham on the Heat disengaged in Combinations, 339 
markable, and distinguishes this salt from the other magnesian 
sulphates. This salt alone of the class forms a thick solution, 
when highly concentrated, and crystallizes with difficulty. It 
was also observed that the protohydrate of sulphate of man-. 
ganese does not dissolve easily in cold water; the quantity of 
the protohydrate employed in the experiments narrated above 
requiring to be agitated with the water for two and a half 
minutes, before the liquid ceased to be turbid and the salt 
was entirely dissolved. ‘The anhydrous sulphate of manga- 
nese was dissolved quickly and with ease. 
III. Sulphates and Chromates of the Potash family. 
1, Sulphate of Potash.—Good crystals of this salt were re- 
duced to powder and sifted. The solution of the equivalent 
quantity, 54°55 grains, in 1000 grains of water, which took 
place in thirty seconds, was attended by a fall of temperature 
in two experiments of 1°50 and 1°52, of which the mean is 
1°51. 
Fall on solution of KO, SO, . . . 1°51, 
The same quantity of sulphate of potash was dissolved in 
a mixture of 300 water-grain measures of dilute sulphuric 
acid of density 1°1 mixed with 700 grains of water. The 
dry acid in the mixture amounted to 36 grains; a single 
equivalent is represented by 25 grains. The solution was 
quite as rapid, or more so, than in pure water; the fall of 
temperature 2°04; the difference of 0°53 is probably con- 
nected with the formation of bisulphate of potash, 
2. Chromate of Potash.—The solution of the equivalent 
quantity, 62°09 grains, of this salt in 1000 grains of water, was 
attended with a fall of 1°18 in water. 
Fall on solution of KO, CrO; . . . 1°18 
When dissolved in an equal quantity of the same dilute sul- 
huric acid as was used with sulphate of potash, the solution 
ie red from the formation of bichromate, and only a ver 
slight change of temperature occurred, namely a fall of 0°08. 
3. Bichromate of Potash.—The fused salt was used, as it is 
easily reduced to a fine powder, and half the equivalent quan- 
tity used, as the whole equivalent is not dissolved by 1000 
grains of water at57° Fahr., thetemperature of the experiments. 
The solution of 47°34 grains, half the equivalent quantity, was 
attended with the same fall of 1°98 in two experiments. No 
sensible change of temperature occurred on diluting this so- 
lution. In the dilute sulphuric acid used with the two pre- 
ceding salts, the fall on the solution of half an equivalent of 
bichromate of potash was 2°00, or sensibly the same as in 
