Science Buddies: "Ask an Expert"

how can i make a selectively or semi permeable membrane

You can use cellophane. This should work nicely.
If you can find at a store sausage casing you could use to do dialysis of some molecules.
Have you tried some thin plastic, the plastic that is used to wrap vegetables for example? (Saran Wrap).
You really need to know which kind of molecules you want to separate. If you try any of the above with water with food coloring and check whether the molecules go through, you may find out which ones are useful

Here is a link to a reverse osmosis experiment.

http://www.ehow.com/how_7793596_run-rev ... mosis.html

Michael

Reverse osmosis (RO) is a membrane-technology filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a selective membrane. The result is that the solute is retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side.