AbstractSodium stannate stabilises commercial hydrogen peroxide by virtue of the stannic acid colloid formed on hydrolysis. The mechanism by which the sols are precipitated by aluminium ions, reported in Part I, explains the process by which sodium stannate stabilises commercial hydrogen peroxide against decomposition catalysts such as the polyvalent ions, Fe3+, Cr3+and Cu2+. The hydrolysis equilibria of these ions are automatically adjusted to the formation of the stable FeOH2+, CrO+and CuOH+ions, respectively, which are strongly adsorbed on the stannic acid colloid and thereby deactivated. These catalytic ions may only be present in minute amounts in non‐stabilised commercial hydrogen peroxide (pH ∼ 4·5), mostly in the heterogeneous state. The equilibrium between the heterogeneous and homogeneous phase is disturbed sufficiently to permit the formation of ionic species which are subsequently deactivated by this pro