Relative importance of convection and diffusion in binary liquid systems subject to small horizontal temperature gradients

By comparing the convection and diffusion transport times of a binary liquid mixture contained in a rectangular box subjected to a small horizontal temperature gradient we roughly estimate the size of an accidental temperature gradient that can be allowed without keeping an experiment away from effective equilibrium. This approximate criterion is then tested against an experiment that is independently known to have equilibrated [G. Maisano, P. Migliardo, and F. Wanderligh, J. Phys. A 9, 2149 (1976)], and we find that the experiment was close to our predicted borderline.