Turbidity very near the critical point of methanol-cyclohexane mixtures

We have measured the turbidity of a critical mixture of methanol and cyclohexane extremely close to the consolute point. The data span the reduced-temperature range 10^-7<t<10^-3, which is two decades closer to Tc than previous measurements. In this temperature range the turbidity varies approximately as lnt, as expected from the integrated form for Ornstein-Zernike scattering. A thin cell (200-{μ}m optical path) with a very small volume (0.08 ml) was used to avoid multiple scattering. A carefully controlled temperature history was used to mix the sample and to minimize the effects of critical wetting layers. The data are consistent with a correlation-length amplitude ξ₀=3.9±1.0 {}, in agreement with the value 3.5 {} calculated from two-scale-factor universality and heat-capacity data from the literature.