Colloids

When the dispersed phase is solid and dispersion medium is liquid, then the colloidal system is called sol.

Colloidal particles possess some type of electric charge. The migration of colloidal particles under the influence of an electric field is known as electrophoresis.

The protective action of different lyophilic colloids is expressed in terms of gold number. Smaller the gold number, the greater is the protective action of the given protective colloid.

sol carries charge because of the adsorption of ferric ions as

is a positive sol hence the best coagulant for the precipitation of is . The precipitating effect of an ion on dispersed phase of opposite charge increases with the valence of the ions.