visking

Visking tubing, sometimes spelled visking or Visking, is a type of semi-permeable cellulose dialysis tubing used in laboratory demonstrations of osmosis and diffusion. It consists of thin walls of regenerated cellulose that form a flexible, cylindrical tube closed at both ends. The membrane permits water and some small solutes to pass through while restricting larger solutes, allowing the enclosed solution to exchange solvent with its surroundings.

In teaching labs, Visking tubing is soaked, flushed, and filled with a test solution (for example a sugar or salt solution). The tube is then immersed in distilled water or another solvent, and changes in mass or volume over time are used to quantify osmotic flow. For diffusion experiments, small colored or detectable solutes inside the tube diffuse out into the surrounding medium, illustrating rate processes and membrane selectivity.

Properties and handling: The tubing is made from regenerated cellulose and is sensitive to long exposure to hypotonic or hypertonic solutions; cleaning and pre-soaking is necessary to remove preservatives. It should be rinsed to remove any preservatives before use.

History and context: Visking tubing has been widely used in physiology and biochemistry education since the mid-20th century as a simple, visual model of cellular membranes. Commercial suppliers continue to offer visking/Visking dialysis tubing, though modern teaching labs increasingly use alternative membranes or digital simulations.