1. The specific viscosity of a dilute solution of polystyrene or rubber is strongly dependent on the nature of the solvent; the specific viscosity is high in a good solvent, and low in a poor solvent or a solvent-nonsolvent mixture. This has been interpreted as being due to changes in mean molecular shape. The specific viscosities of cellulose acetate solutions are not so sensitive to the nature of the solvent. 2. The extrapolated specific viscosity at the limit of solubility is in the same range for several different solvent-nonsolvent systems. 3. The effect of a temperature increase is to lower the specific viscosity of rubber or polystyrene solutions in a good solvent, but to increase the specific viscosity in a mixture of solvent and nonsolvent. 4. The specific viscosity of a dilute polystyrene solution is more nearly linear with concentration in a toluene-methanol mixture than in pure methanol. The quadratic term b in the equation: sp=ac+bc2)⁠, is reduced relatively more than the linear term a by the presence of the nonsolvent.

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