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Object:
To demonstrate the phenomenon of dialysis with the help of a collodion bag.
Requirements:
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Collodion bag, starch, salt, thread, beakers, water, iodine, silver nitrate, collodion (cellulose nitrate dissolved in ether and alcohol).
Method:
(a) Preparation of collodion bag:
1. Pour a small amount of collodion in a wide mouthed, clean and dry tube.
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2. Revolve the tube so that collodion gets evenly distributed and cover the interior wall of the tube.
3. Pour back the extra collodion and wait for about 10 minutes to let it dry.
4. Add one more coating of collodion exactly in the way followed above, and let it dry for 4 to 6 hours.
5. Remove the membrane by gently pouring the water in between the glass and the membrane, and the latter may be preserved in distilled water containing few drops of toluol.
6. Thus formed collodion bag can be utilized as a semipermeable membrane.
(b) Phenomenon of Dialysis:
7. Fill the collodion bag with a mixture of starch and solution of common salt.
8. Keep the collodion bag in a beaker containing water after closing its mouth with a thread (Fig.6).
9. After some time test the water of beaker for sodium chloride with the help of silver nitrate, and also for starch with the help of iodine.
Observations:
Tests indicate that water gives positive test for sodium chloride and negative or no test for starch.
Results:
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Tests of the water indicate that macromolecules like starch are retained inside the bag and thus not giving the test in water with iodine, while the small molecules and ions (Na+, CI–) pass out readily into the surrounding water and thus gives positive test of sodium chloride. Thus the experiment shows the phenomenon of dialysis.
