Visking tubing is an artificial partially permeable membrane:
The slideshow shows a typical experiment using Visking tubing and sucrose solution:
Visking tubing experiment
The sucrose solution is hypertonic to the water – it is a more concentrated solution. There is a net movement of water molecules, by osmosis, from the water outside to the sucrose solution inside the Visking tubing. This makes the liquid level in the capillary tube rise.
A less concentrated solution is hypotonic to a more concentrated solution, while two solutions at the same concentration are isotonic.
The table summarises the results of the four combinations of water and 10% sucrose in the experiments, showing the movement of water and solute across a concentration gradient.
|Liquid outside||Liquid inside||Water moves||Solute moves||Result|
|Water||10% sucrose||Outside → inside||Inside → outside||Liquid level rises|
|10% sucrose||Water||Inside → outside||Outside → inside||Liquid level falls|
|Water||Water||No movement||No movement||No visible change|
|10% sucrose||10% sucrose||No movement||No movement||No visible change|