The influence of solute concentration on measurements of the viscosity and sedimentation properties of DNA solutions is very great. Enough data has been accumulated in recent years, however, to permit a quantitative description of these concentration effects for DNA samples of molecular weight below roughly 16·106. It has therefore become possible to measure [η] and s0 (and indirectly molecular weight) for such samples from single measurements on generally available equipment. Above molecular weight 16·106 the possibility of such a simplification is at present excluded by the magnitude of the concentration effect in sedimentation and the gradient effect in viscosity, plus the newly studied phenomenon of speed dependence in sedimentation. It is shown, however, that rotor speed does not influence the sedimentation of samples up to molecular weight 16·106 until a critical high velocity is reached.
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