An apparatus designed to demonstrate *osmosis
and to measure osmotic pressure (water potential). One form of osmometer consists of a porous pot, rendered semipermeable by impregnation of its pores with copper ferrocyanide. The pot is filled with the solution under investigation and a piston placed on the solution. The pot is then immersed in a container of distilled water. Water passes by osmosis into the porous pot and lifts the piston until the force of the water entering the pot equals the hydrostatic pressure created by the weight of the piston.