Page:Outlines of Physical Chemistry - 1899.djvu/249

 results obtained by Berthelot and PSan de Saint-Gilles are given in the following table :

�� �Substances

�employed

� �Value oi

�\x

�Aoid (a)

�Alcohol

�(&)

�Ester (a t )

�Water (& t )

�Calculated

�Observed

� �—

�—

�—

� �—

�—

� �—

�—

� �—

� �—

� �—

�—

�—

��Experiment and theory do not absolutely agree, still the agreement is quite sufficient.

Second Example. Action op an Acid on a Salt in Aqueous Solution. — As we consider here reactions in which no precipitation occurs, the division of the base between the two acids could not be determined by chemical analysis. But physical chemistry teaches us several methods of investigating the problem, and we shall here consider the two principal ones.

a. Study of the thermal effect of the reaction (in dilute

In speaking of neutralisation phenomena, we have omitted to mention an indirect method of determining the difference of the heats of neutralisation of two salts. When an equivalent of sodium sulphate (£ gram-molecule) reacts on an equivalent of nitric acid (1 gram-molecule), a certain thermal effect is produced. Quite a different thermal effect results from the action of an equivalent of sulphuric acid on an equivalent of sodium nitrate. The final equilibrium is the same in both cases ; the difference in the observed effects

1 In order to give an account of this work of Thomseri's we shall take up the old view of the constitution of salt solutions, and in the meantime let us forget the theories discussed at the end of the third part of the book.

�� �