342 Mr. Graham on the Heat disengaged in Combinations. 
Of anhydrous chromic acid an equivalent, 32°59 grains, was 
dissolved by 1000 grains of water with a rise of 0°51. A se~ 
cond equivalent, dissolved in the previous solution, produced 
a rise of only 0°38. ‘The relations of this acid to water are 
therefore very different from those of sulphuric acid. ’ 
5. Sulphate of Soda.—In removing the hygrometric water 
which the crystals of this salt generally contain in large quan- 
tity, by pressure in blotting-paper, the salt is apt to lose a 
little of its combined water. ‘The crystallized salt contained 
as determined by analysis, to 100 sulphate of soda, 121°5 
water, instead of 126°1 water, which are ten equivalents. The 
equivalent quantity of the fully hydrated salt is 100°85 grains, 
but of the salt under examination only 98°79 grains. The last 
quantity, which contains 54°2 grains of water, was dissolved 
in 946 grains of water in half a minute, with a fall of 4°:43. 
The fall is almost entirely due, as will immediately appear, to 
the liquefaction of the combined water of the salt, of which 
the quantity liquefied in the experiment was 54°2 grains in- 
stead of 56°2, the ten equivaletits. The fall of 4°45 increased 
in the proportion of 542 to 56:2, becomes 4°59. 
Fall on solution of NaO,SO,+10HO . . 459. 
The same quantity of the salt was dissolved in the diluted 
sulphuric acid of the experiments with the previous salts, with 
a fall of 5°00; which, corrected in the same manner as the 
last result, gives a fall of 5°19 for the equivalent of the salt. 
Hence the fall on the solution of the sulphate of soda in dilute 
sulphuric acid is 0°60 greater than in pure water; a circum- 
stance connected probably with the formation of bisulphate of 
soda. 
Sulphate of soda was made anhydrous by a strong heat, 
without being fused. ‘The solution of the anhydrous salt is 
difficult, owing to the instantaneous formation of a hard co- 
herent mass when the salt is thrown into water, which it fe- 
quires two or three minutes to break up and dissolve. Very 
little change of temperature occurs. A rise took place in one 
experiment of 0°10. In another experiment, in which the 
salt was added in a gradual manner with constant stirring, 
there was less caking, and the solution more rapid, although 
it still required two minutes. A rise occurred of 0°18. The 
last experiment is most to be depended upon. The results 
for the sulphate of soda will therefore be,— 
Rise on solution of NaO, SO, « . « « O18 
Fall on solution of NaO,SO,+ 10HO. 4°59 
Whole heat disengaged by NaO, SO,. «4°77 
The last number represents the heat evolved in the formation 
