Optical Measurements of Gravitationally Induced Concentration Gradients near a Liquid-Liquid Critical Point

Using a laser-beam deflection technique and a 1-mm-high sample, we have determined, for the first time, the magnitude of the steady-state concentration gradient due to the gravitational field in a binary mixture near a consolute critical point. The data have been taken, as a function of T-Tc, along the critical isochore. A strong γ-type divergence is observed. A comparison with the values calculated by use of our own set of osmotic compressibility data is also presented.