Measurement of negative Soret coefficients in a vertical fluid layer with an adverse density gradient

Using a thermogravitational cell, we have measured the Soret coefficient of the binary liquid systems formed by benzene and toluene with methanol and ethanol. The existing data in the literature present large deviations, particularly in the low alcohol concentration range in which the Soret coefficient is negative. It is shown that the thermal gradient maintains an adverse density gradient in the vertical fluid layer. When the thermal gradient is suppressed, the density gradient reverses, and recovers the adverse initial value when the thermal gradient is reestablished.