The Problem of a Theoretical Calculation of the Velocity of Sound for Binary Liquid Mixtures

Seshadri and Reddy [1] have calculated the velocity of sound for eight mixtures of cyclohexane with other fluids by the molecular kinetic theory of Schaaffs and by the theory of free lengths of Jacobson. They compared the results with the measured values. The divergences are relatively great. Seshadri and Reddy thereby presume the theory of Jacobson to be superior.

The molecular kinetic calculations however show considerable errors, because wrong molecular volumes and collision factors were used. By application of the correct formulae and data a nearly perfect agreement between measurement and theory using the molecular kinetic theory is obtained, both by the direct method with the molecular acoustic equation for sound velocity and by the indirect method with the molar acoustic volume.

It is shown that the agreement between measurement and the molecular kinetic theory comes from the fact that the molecules are treated as a real non-elastic substance, whereas in the theory of free lengths they are rigid spheres.