Critical behavior of the binary-fluid isobutyric acid-water with added ions (K+, Cl-)

Measurements of the coexistence curve of the binary-fluid mixture isobutyric acid + water with added KCl salt at various concentrations: show an important dependence on the critical temperature and the critical exponent beta. The phase-transition region shifts as a function of the salt concentration. The effective -critical exponent beta* = (0.266-0.293) is neither compatible with the Ising value beta = 0.325 nor with the Fisher renormalized value similar to 0.365.