A Rotational Viscometer Capable of Precise Measurement at Very Low Rate of Shear

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Abstract
A rotational viscometer with high accuracy at very low rate of shear (0.05 1/s) is constructed. It is a viscometer of free suspension type which is devised so as to reduce the influence of surface tension and the error due to excentricity. The expected error of the measurement can be so small as 0.02%. By means of this apparatus an anomaly of dip type in the curve of η s p /C vs. C for highly diluted solutions (η s p ≃0.05) of polystyrene (mol. wt. 9.7×104) in toluene is observed. For the same dilution of DNA in water with 0.1 mol. NaCl an anomaly of peak type is observed. These anomalies are quite similar to the anomalies Cragg and Bigelow have observed in ternary systems and interpreted as the effect of critical concentration.