Coexistence curves of electrical conductivity in critical solution: isobutyric acid–water with added ions

Abstract

Comprehensive results of temperature (T) studies of electrical conductivity (σ) in the one-and-two phase regions of the binary fluid mixture of isobutyric acid–water (IBAW) with X M[KCl] at various critical concentrations are presented. A strong asymmetry of the coexistence curves as determined causes a strong violation of the law of rectilinear diameter. The obtained critical anomalies in the homogeneous phase σcrit (T) or the diameter of the σd (T) are associated with the same critical exponent θ = 1 − α ≈ 0.88, where α is the specific heat critical exponent. For the mixture with critical composition, the two phase regions show a concentration behavior with σl − σu ≈ |−t|β. The phase transition region shifts as a function of the salt concentration. The effective critical exponent β* = (0.264–0.296) is neither compatible with the Ising value β = 0.325 nor with the Fisher renormalized value ∼0.365.