Tracers, Transfer through Membranes, and Coefficients of Transfer.

The rate of flow of a tagged species of a material substance through a permeable membrane is proportional to the rate of flow of the substance itself when, and only when, the species mole fraction of the substance is the same on both sides of the barrier. The ratio of the osmotic transfer coefficient of a substance in a particular barrier to the exchange coefficient, determinable with a tracer, is greater than 1.