A sintered solid of silica $5mm$ thick is porous, with a void fraction $$ of $0\mathrm{.}30$ and a tortuosity $$ of $4\mathrm{.}0.$ The

pores are filled with water at $298K.$ At one face, the concentration of $KCl$ is held at $0\mathrm{.}10mo\frac{l}{l}$iter, and

fresh water flows rapidly past the other face. Neglecting any other resistance but that in the porous solid,

calculate the diffusion of $KCl$ at steady state.