The speeds of sound in water measured by Del Grosso and Mader [J. Acoust. Soc. Am. 52, 1442–1446 (1972)], Kroebel and Mahrt [Acustica 35, 154–164 (1976)], and Fujii and Masui [J. Acoust. Soc. Am. 93, 276–282 (1993)] were compared. A fairly good agreement was found. A new fifth-order polynomial describing the dependence of the speed of sound in water on temperature (ITS-90) within the limits 0–95 °C was proposed. The importance of the effect of impurities of water on the systematic errors of the measurement results was pointed out. The accuracy of the relative measurements of speed of sound in liquids was discussed in the context of the proper choice of a standard (“true”) value of the speed in water.

Previous experiments demonstrated that microheterogeneities occur in liquid systems (2-methylpyridine or 2,6-dimethylpyridine) + water. They are most probably due to the association of the hydrates through hydrogen bonds between water molecules. Substitution of methanol for water causes that the mixtures become homogenous. The results of viscometric studies reported in this study confirmed that the molecular clusters in aqueous solutions are much larger than the complexes occurring in the methanolic systems. Taking into consideration “kinetic entities” rather than monomeric molecules, the dependence of viscosity on concentration and temperature have been satisfactorily approximated by the Grunberg–Nissan relation with two adjustable coefficients. The kinetic entities were trimers of water, dimers of methanol, and monomeric amines. The same approach proved to be valid for the activation energy of viscous flow as well.