Polystyrene colloids were obtained by emulsion polymerization using the silvcr/bisulfite redox initiation system. The colloid stability of this system against the addition of different types of electrolytes has been studied. The results showed that the slope of the coagulation curves did not exhibit a dependence upon the counterion valence and the CCC did not follow the Schulze-Hardy rule.The Hamaker constants calculated from the CCC’s values were in reasonable agreement with those found by previous workers. The surface potential φ of this polystyrene colloid

which was calculated from the charge density obtained by conductometric titration

was approximately equal to φ_δ determined from the slope of the coagulation curves. The coagulation processes can be easily and accurately followed by means of 90° light scattering measurement. When the particle sizes were large compared with the wave length of the incident light

the optical angle for the measurement of scattering must be used

which could be calculated by Lips-Willis equation