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

Comprehensive results of temperature (T) studies of electrical conductivity (sigma) 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 sigma(crit) (T) or the diameter of the sigma(d) (T) are associated with the same critical exponent theta = 1- alpha approximate to 0.88, where alpha is the specific heat critical exponent. For the mixture with critical composition, the two phase regions show a concentration behavior with sigma(1) - sigma(u) approximate to vertical bar-t vertical bar(beta). The phase transition region shifts as a function of the salt concentration. The effective critical exponent beta* = (0.264-0.296) is neither compatible with the Ising value beta = 0.325 nor with the Fisher renormalized value similar to 0.365.