Effect of gravity on osmotic equilibria.

Experiments with colloidal suspensions of oil and iron oxide at equilibrium show that the buoyancy of the suspended particles is additive to the osmotic pressure and that the relation remains with the free surface and not with the membrane. The experiments contribute to the general concept that osmotic pressure is caused by the dispersal pressure of solute molecules and that the osmotic interaction with the water at equilibrium is due solely to a coupling at the free surface.