This is a standard method for determining the properties of precipitated hydrated silica (commonly known as white carbon black), a key reinforcing filler in the rubber industry. The core of this method lies in utilizing the characteristic adsorption of cetyltrimethylammonium bromide (CTAB) molecules onto the external surface of silica particles under specific conditions. Due to the large molecular size of CTAB, it cannot penetrate the fine pores inside the material. Therefore, by measuring its adsorption amount via titration and calculating the specific surface area, this method accurately reflects the "external surface" area of silica that can effectively interact with rubber polymer chains during the mixing process. This method provides a crucial technical basis for evaluating and regulating the reinforcing performance of silica in rubber.