Gold number is defined as the minimum amount of lyophilic colloid in milligrams, which prevents the flocculation (coagulation) of 10‌mL gold sol (containing 0.5 to 0.06g of gold per litre) by the addition of 1‌mL of 10%NaCl solution. More is the gold number, less is the protective power of the lyophilic colloid, since it means that the amount required is more,