Brownian movement enables us,
(i) to calculate Avogadro number.
(ii) to confirm kinetic theory which considers the ceaseless rapid movement of molecules that increases with increase in temperature.
(iii) to understand the stability of colloids: As the particles are in continuous rapid movement they do not come close and hence not get condensed.
(iv) That is Brownian movement does not allow the particles to be acted on by force of gravity.

(i) Using a colloid mill, the solid is ground to colloidal dimension.
(ii) The colloid mill consists of two metal plates rotating in opposite direction at very high speed of nearly 7000 revolution I minute.
(iii) The colloidal particles of required colloidal size is obtained by adjusting the distance between two plates.
(iv) By this method, colloidal solutions of ink and graphite are prepared.

The adsorption theory explains the following
(i) Increase in the activity of a catalyst by increasing the surface area. Increase in the surface area of metals and metal oxides by reducing the particle size increases the rate of the reaction.
(ii) The action of catalytic poison occurs when the poison blocks the active centres of the catalyst.
(iii) A promoter or activator increases the number of active centres on the surfaces.

(i) In certain reactions one of the products formed acts as a catalyst to the reaction.
(ii) Initially the rate of reaction will be very slow but with the increase in time the rate of reaction increases.
(iii) Auto catalysis is observed in the following reactions.
\({ CH }_{ 3 }COO{ C }_{ 2 }{ H }_{ 5 }+{ H }_{ 2 }O\longrightarrow CH_{ 3 }COOH+{ C }_{ 2 }{ H }_{ 5 }OH\) 
Acetic acid acts as the auto catalyst.
(iv) \(2As{ H }_{ 3 }\longrightarrow 2As+{ 3H }_{ 2 }\) 
Arsenic acts as an autocatalyst.