Surface tension of a two-component liquid mixture near its critical solution point

We measure the liquid–vapor surface tension of solutions of isobutyric acid and water as a function of temperature and composition in the one-liquid-phase region near the critical solution point, and compare the results with the predictions of theory. Surface waves of small amplitude and known frequency are generated by an electrostatic transducer, their wavelengths determined by diffraction of a laser beam, and the surface tensions calculated from the known dispersion law. The measured surface tensions are displayed as a function of a single scaled temperature and composition variable as suggested by theory. The experimentally determined scaling function is qualitatively of the predicted form.