Purification of Colloidal Solution





Various techniques for purification of colloidal solution are as follows:

1.  By Dialysis: It is done by dialysis. Dialysis is the process which is used for the separation of crystalloids from a colloid by filtration or diffusion through parchment paper or animal membrane. The apparatus employed for this purpose is called dialyser. This process is based on the fact that membranes contain very small pores through which only dissolved molecules and ions of the true solution can pass readily.

The Graham dialyser consists of a hollow cylinder open at both ends, over one end of which a membrane is tied. The colloidal solution to be dialysed is placed in this cylinder which is then suspended in a large vessel containing flowing distilled water. After several hours all the molecules or ions of the crystalloid pass though the membrane leaving behind pure colloidal solution.

This process is very slow, but it can be quickened some what by using hot water or by applying an electric field if the substance in true solution is an electrolyte and removed under electric field then it is known as electro-dialysis. In this case, the ions of electrolyte readily pass through the membrane due to electrostatic pull of oppositely charged electrodes.

Hemi dialysis: Here blood of such patients is cleaned by artificial machines whose kidneys are damaged or mal functioning.

2. Ultra filtration: Here colloids are separated from crystalloids with the help of ultra filter papers. Which are obtained by treating simple filter paper with gelatin or collodion so, that the pores become less or narrow in size through which only crystalloid particles can pass.

3. Centrifugation: Here impurities are removed from colloids with the help of a machine of high speed called centrifugal machine. Here colloids settle down while impurities remain in centrifuge.



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