gold number is measurement of efficiency of the protective colloid, how and why?

Gold number is a term used in colloidal chemistry. It is defined as the minimum amount of lyophilic coloid in milligrams which prevents the coagulation of 10 ml gold sol against 1 ml of 10%NaCl solution.

Coagulation of gold sol is indicated by colour change from red to blue when particle size just increases. More is the gold number less is the protective power of the lyophilic colloid since it means that the amount required is more.It was first used by Zsigmondy.The amount is taken in terms of weight in milligrams.

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