what is berkley and hartley"s method of osmatic pressure

It is used to measure the osmotic pressure of two solution of different concentration separated by semi-permeable membrane.

Procedure: In this method there are two cylinder one covering other and separated by semi-permeable membrane as shown in figure below. On end is connected by theisel funnel called and other end by capillary tube to measure the height of solution filled in inner cylinder.

The upper layer of cylinder is connected with piston and pressure gauge apparatus. In the outer cylinder concentrate solution is filled while in the inner cylinder dilute solution like water is filled. When osmosis take place the height in capillary tube decreases while the piston moves in upward direction. In order to maintain, the same height on capillary tube, the pressure over piston is applied. The minimum pressure which is applied to maintain the same height in capillary tube is measured by pressure called which is called osmotic pressure.