state of dispersed phase and dispersion medium. S.No. Dispersion medium Dispersed phase Name of the colloid Examples . Gas Liquid Liquid Aerosol Fog Aerosol spray .
Gas Solid Solid Aerosol Smoke, Air pollutants like fumes, dust. . Liquid Gas Foam Whipped cream, Shaving cream, Soda water, Froth. .
Liquid Liquid Emulsion Milk, Cream, Mayonnaise . Liquid Solid Sol Inks, Paints, colloidal gold. XII U10-Surface XII U10-Surface - - - - . Solid Gas Solid foam Pumice stone, Foam rubber bread.
. Solid Liquid Gel Butter, cheese . Solid Solid Solid sol Pearls, opals coloured glass alloys colloidal dispersed eutetics. .
. Preparation of Colloids Many lyophillic substances are made in their colloidal form by warming with water. Rubber forms colloidal solution with benzene. Soap spontaneously forms a colloidal solution by just mixing with water.
In general, colloidal are prepared by the following methods. i. Dispersion methods: In this method larger particles are broken to colloidal dimension. ii.
Condensation method: In this method, smaller atom or molecules are converted into larger colloidal sized particles. ) Dispersion methods (i) Mechanical Dispersion: Using a colloid mill, the solid is ground to colloidal dimension. The colloid mill consists of two metal plates rotating in opposite direction at very high speed of nearly revolution / minute. Colloid mill Coarse dispersion Figure .
Colloid mill The colloidal particles of required colloidal size is obtained by adjusting the distance between two plates. By this method, colloidal solutions of ink and graphite are prepared. XII U10-Surface XII U10-Surface - - - - (ii) Electro Dispersion: A brown colloidal solution of platinum was first prepared by George Bredig in . An electrical arc is struck between electrodes dispersed in water surrounded by ice.
When a current of amp / V is passed an arc produced forms vapours of metal which immediately condense to form colloidal solution. By this method colloidal solution of many metals like copper, silver, gold, platinum, etc. can be prepared Alkali hydroxide is added as an stabilising agent for the colloidal solution. Svedberg modified