A polystyrene fraction of molecular weight 500,000 (determined by light scattering) was used in the investigation. Polystyrene solutions in benzene, ethylbenzene, toluene, carbon tetrachloride, monochlorobenzene, cyclohexane and decalin were investigated. All solvents, except deealin, were carefully purified in a special distillation apparatus t equipped with thight glass filters to protect the liquid from dust entering from the air. Decalin was not distilled, but repeatedly filtered through a No. 4 glass filter. The refractive indices of the solvents agreed with literature data. The absence of dust in the solvent was established from the complete disappearance of the asymmetry of light scattering. Polystyrene solutions of up to 10 g/dl concentration were studied; 10% polystyrene solutions in aromatic hydrocarbons, CC14, chlorobenzeno and decalin were repeatedly (5-6 times) centrifuged for 50 minutes. A T-14 centrifuge was used with g=20,000 and an optimum speed of 15,000 rev/min. After each centrifuging angular asymmetry z ' = R45/Rl~ 5 and R90 was determined for separate samples. Purification was considered complete when the measured values ceased to vary. The concentration of the purified solutions was determined gravimetrically. To control the degree of purification of 10% solutions, 2O/o solutions obtained by dilution were centrifuged in many cases. The observations confirmed that the values of Re0 and z' remained unchanged. Solutions of polystyrene in cyclo-hexane and CC14 were purified from dust by repeated filtration through a No. 4 glass filter at 45 ° and 20°C, respectively. Solutions of lower concentrations were prepared by diluting 10% solutions in a nephelometer cell. After dilution the solutions were kept at the experimental temperature for 24 hours to ensure uniform distribution of solvent. Equil ibrium was evaluated by measuremcnt during excess light scattering of Rp0 and angular asymmetry z', these values being maintained constant for 3-4 hours in practice. Light scattering was studied by means of a nephelometer designed by Soboleva [5] which makes it possible to measure under three angles (45, 90 and 135 °) and directly to