Using a high pressure test cell with windows, laser interference patterns in a 62 mg/l NaCl solution adjacent to the membrane were photographed after the establishment of steady state for 30 atm. constant applied pressure. The mathematical solution of the concentration profile was, with ray tracing, analytically fitted to the experimental interference pattern. From this analysis at 28 * I°C and 30 atm. pressure, an intrinsic salt rejection of R -0.86 * 0.02 and reduced permeation flux of u -100 cm-' for the DDS-990 cellulose acetate membrane was obtained. Limitations of the method, sensitivity and accuracy of the results are also discussed.

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It is shown that by using a multifilter spectrum analyzer one can obtain, by means of light beating spectroscopy techniques, the time evolution of average size and number density of the scatterers. The time evolution is obtained at a rate of 1 min-1. By numerical calculation it is shown that even when the scatterers are not monodisperse the spectrum can be used to calculate the average size with satisfactory accuracy.