ABSTRACT
Maximum rates of migration by diffusion occur in bulk or free water at extreme dilution. The driving force for diffusion is a concentration gradient, or, more correctly, a chemical potential gradient as shown schematically in Figure 6.1. The equation for the mass flux, /, is Pick's first law as follows:
where/is the mass flux produced by the concentration gradient dc/dx [ML~2 T"1], D0 the free
solution diffusion coefficient [L2 T 1], c the solute concentration in the fluid at any point x [ML~3] and x the distance from the highconcentration interface [L].
