Fig 1: Visking Tubing
A cellulose tube used for osmosis experiments.
Visking or dialysis tubing is usually made from regenerated cellulose and looks a bit like sellotape when in its dry form. It is available to purchase from lab suppliers on a roll or in lengths in various diameters. The tubing can be cut to the desired length and tied at one end making a sausage-like open ended tube.
The tubing is used in practicals and demonstrations involving osmosis. Because the cellulose material is semi-permeable, it means that small molecules can pass through its walls whereas larger molecules cannot.
An example of a dialysis demonstration may involve filling a section of tubing with a mixture of glucose and starch. The glucose molecules are very small in comparison to the starch molecules. The sausage-like tube is suspended in a beaker of water and left for set period. The glucose should be able to pass through the walls of the tubing and into the water. The presence of glucose in the water can then be tested for using Benedict’s solution. The starch should stay within the tube.
Most visking tubing available to schools has an approximate average pore radius of 24A and most supply companies list the tubing in sizes which represent the inflated diameter unless stated otherwise.
Visking tubing should be stored in a dry environment away from direct sunlight.
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