Effects of buoyancy and of magnetic forces on osmotic pressure

The commonly held view that the mechanism of osmotic pressure is a mass action effect at the semi-permeable membrane has recently been challenged by several authors who propose that solute molecules, in bombarding the free surface of the solution, subject the solvent to a negative hydrostatic pressure. Thus, they argue that osmotic pressure is a purely hydrostatic phenomenon. Experimental findings that they cite in support of their concept are here analyzed and shown to be consistent with the mechanism of a mass action effect at the semipermeable membrane.