288 OUTLINES OF PHYSICAL CHEMISTEY
Having now given the principle on which this new me- thod of investigation is based, we shall return to the reaction which has already been studied from the thermo-chemical l point of view — namely, the action of £K 2 S0 4 on HN0 3 .
One gram-equivalent of potassium sulphate is dissolved in so much water that the solution weighs 2 kilograms. One gram-equivalent of nitric acid is contained in 1 kilo- gram of solution.
If the reaction
Were to take place completely, there would be an expansion of 8*17 c.c. By the pycnometer we ascertain that a solu- tion of
^K 2 S0 4 has a volume of 1,981*75 c.c. HNO3 „ „ „ 966-60 „ KNO3 „ „ „ 1,938-11 „ iH 2 S0 4 „ „ „ 968-41 „
The sum of the first two volumes is less by 8*17 c.c. than the sum of the last two.
But certain secondary reactions must be taken into account.
Between the two salts and between the two acids no volume reactions take place. For the action nitrate -f nitric acid it is negligible ; but the action of sulphuric acid on the sulphate is quite considerable. Ostwald gives :
��expansion = 8*545 c.c. = 4-625 „ = 4-900 „
��>>
a
��From these data the volume change which accompanies the establishment of a certain state of equilibrium can be calculated. Suppose that in the reaction under examina-
1 Thomsen has shown by a thermo-chemical method that for the alkalis (not only for NaOH, but also for KOH, and NH 8 ) the avidity of nitric acid and that of sulphuric acid are in„the ratio 2 : 1.
�� �
