Under suitable conditions, the coagulation of GR-S latex by sulphuric acid has been found to exhibit second order rate characteristics, and to be represented by the equation,whereCis the concentration of polymer at timet,C0is the initial concentration of polymer, and (H+)′ is the concentration of H+ion in excess of the critical concentration necessary to initiate coagulation. Coagulation is accompanied by desorption of soap from the surface of the latex particles, and the variation of surface tension resulting from this follows the equation log γ = A − Blogt, where γ is the surface tension andAandBare constants. Appropriate adjustment of the temperature was found to stabilize the emulsion markedly in the presence of acid. A mechanism for the coagulation process is considered.