The coagulation power of an effective ion carrying the charge opposite to the sol particles has been illustrated by.

• The amount of electrolyte required to coagulate a specific amount of colloidal solution is determined by the valency of the coagulating ion (ion having a charge opposite to that of the colloidal particles). Hardy and Schulze's observation is known as Hardy Schulze Law. The key points can be summarised as follows:

(a) The electrolyte ions that are efficient in causing coagulation are those that have the opposite charge as the colloidal particles. These ions are known as coagulating or flocculating ions.

(b) The larger the valency of the coagulating or flocculating ion, the greater its ability to cause coagulation.