The changes occurring in the angular distribution of scattered light during the rapid coagulation of a polystyrene latex (diam. 126 nm) have been measured at two wavelengths for times up to the halflife, and compared with those calculated from theory in which the number concentration of the aggregates are taken to be those given by von Smoluchowski's second-order kinetics and in which the scattering properties of aggregates are described in terms of optical interference between their constituent primary particles. The agreement was good but absolute intensity measurements on the initial latex dispersion differed from those calculated from the Mie theory in a manner indicative of partial aggregation. When this was taken into account, excellent agreement between the measured and calculated angular distributions was obtained at all angles between 30 and 135" at both wavelengths for times up to the half-life. The absolute rate constant for rapid coagulation was 67-69 % of the theoretical Smoluchowski value.

The Rayleigh ratio of the light scattered at 90" by solutions of three simple electrolytes has been measured with high precision using a modified Brice Phoenix light-scattering photometer. From the results obtained at wavelengths 546 and 436 nip the contribution R,f. to the scattering due to fluctuations in concentration of the solute has been calculated from the total isotropic scattering of the solutions and the contribution &.f. from the density fluctuations on the system. The quantities Kc/R,.f. so obtained are compared with (-a In ao/ ~C ) ~, T obtained from activity data. Also included are measurements on the refractive index, refractive index increment and depolarization of the solutions at wavelengths 546 and 436 mp.

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