Soret coefficient and the two-component Bénard convection in the benzene-methanol system

When heated from below, layers of binary solutions with negative Soret coefficients present heating curves with characteristic shapes: A negative slope exists in the vicinity of the convection onset and a hysteresis appears. In the literature the values of the Soret coefficients for diluted solutions of methanol in benzene are generally reported as negative. In very carefully executed B\'enard experiments with this system, we do not observe heating curves with such negative slopes. Our measurements, using convection in order to quantify the concentration gradients, are not in agreement with the reported Soret coefficient values.