Dialysis tubing

Dialysis Tubing is a type of semi or partially permeable membrane tubing made from regenerated cellulose or cellophane. It is used for diffusion, or more accurately osmosis. It allows the passage of small molecules but not larger ones. It is used in clinical circumstances to ensure a filtered flow of molecules, preventing the flow of larger solute molecules. Small molecules can be 'washed' out of a solution which is pumped through the tubing into a solvent, usually water, which surrounds it and in which they can be flushed away.

In demonstrations of semi-permeable membranes, a solution containing several types of molecules, usually glucose and starch, is placed into a semipermeable dialysis bag, such as a cellulose membrane with pores, and the bag is sealed. The sealed dialysis bag is placed in a container of a different solution, or water. Molecules small enough to pass through the tubing (water, salts, monosaccharides, and other small molecules) tend to move into or out of the dialysis bag in the direction of decreasing concentration, therefore displaying diffusion. Larger molecules (such as proteins, or polysaccharides) that have dimensions significantly greater than the pore diameter are retained inside the dialysis bag.