Data for: Phase Rule Classification of Physical and Chemical Critical Effects in Liquid Mixtures

The isobaric heat capacity and the coefficient of thermal expansion of a binary liquid mixture with a critical point of solution diverge as functions of temperature in the critical region. When the same liquids are used as solvents for chemical reactions, the van’t Hoff plot of the extent of reaction diverges in the critical region. According to the phase rule, the physical and chemical properties are isomorphic in the sense that in each case the critical behavior is determined by three fixed thermodynamic intensive variables. The predicted chemical effects are demonstrated by measuring the solubilities of lead salts, alone and together, in a mixture of isobutyric acid + water, which has a upper critical point of solution near 26 degrees C.