Brownian Movement:- In 1828, an English Botanist Brown observed that pollen grains suspended in water execute a continuous ig-zag motion. He named this phenomenon as Brownian movement. Later on it was found that the particles of the dispersed phase of all colloidal solutions also execute a continuous zig-zag motion (in the figure).

A proof of Brownian movement in furnished if we watch the smoke particles in the beam of light in a cinema hall. The smoke particles continue to move ceaselessly in a zig-zag fashion.

Cause of Brownian movement:- The dispersed phase particles of the colloidal solution are being constantly colloided by the molecules of the dispersion medium. It was stated by Wiener is 1863 that the dispersed phase particles increases, then the chances of unequal bombartment decrease. This can be confirmed by the fact that the suspensions do not show any such movement due to large molecule size.

Significance:- This movement opposes the force of gravity. On the colloidal particles. As a result, these particles always remain in the state of motion and do not settle.

This is responsible for the stability of the colloidal solution.