Endosmose

Endosmose, in Physios, signifies the passage of a fluid through a membrane or other porous partition, there being another fluid on the other side. This is illustrated by the endosmometer, which consists of a glass tube at one end of which a membranous bag is fixed. If the bag be then filled with milk and immersed in a vessel of water it will be found that the liquid within the instrument gradually rises to fill the tube, and the water level outside gets lower. This is due to a process of diffusion of each liquid through the membrane; but more water passes in than milk passes out, and there is a resultant rise of level inside. The inward flow to higher level is called endosmose, and the smaller outflow to lower level is called exosmose.

For the action to take place it is necessary that the liquids should be capable of mixing, that they should be of different densities, and that the membrane should permit at leeist one of the liquids to flow through. The rate of diffusion depends on the substance in solution, on the strength of the solution, and on its temperature. A similar piece of apparatus, with a porous earthenware jar instead of the membrane, may be used to exhibit similar effects with gases.