AbstractExperiments with polystyrene are described (a) to illustrate the difference between viscosity‐average and number‐average differential distribution curves and (b) to test the nature and the efficiency of the fractionation process. The viscosity‐molecular weight relationship for dilute solutions of high polymers is critically reviewed. Evidence is presented which suggests that during fractionation successive fractions have differing distributions. This indicates a lack of precision in the evaluation of the andKof the Houwink equation, and the absence of objectivity in the method of plotting differential distribution curvesviatheir stepwise and integral c