have shown that in dilute solution the surface tension increases linearly with concentration: thus we see from Eq. (13) that the surface concentration must be directly proportional to the bulk concentration. In practice, the surface tension often drops initially at very low concentra tions and then rises this effect is small and will not influence the present results.
The ratio B has dimensions of length and is a measure of the effective thickness of the region at the surface in which the actual concentration is significantly less than bulk concentration. we may consider a very crude picture in which the actual concentration may be supposed to be zero from the surface inward to a distance xo and to be equal to the bulk concentration from that distance inward. It will easily be seen from Eq. (4) that