stances dissolved in water. Then, Pfeffer, by allowing the precipitation to take place in the walls of vessels of earthenware, secured for the membrane sufficient support so that measurements could be made of the force with which water passes into solutions of various kinds in cups clothed by semipermeable membranes and immersed in water. The resulting pressure is known as "osmotic pressure," and is nearly proportional to the concentration of, i. e., the number of molecules