The number of milligram of the protective colloid that prevents the coagulation of 10ml of red gold sol is known as gold number. When 1ml of a 10 percent solution of sodium chloride is added to it, Here, Gold number of Hb=0.03 As, weight of Hb require for 10ml of gold is 0.03mg, thus, weight require for 50ml of gold solution is 0.15mg