Viscosity of Binary Mixtures

Abstract

IN a recent communication¹, Mr. A. J. A. van der Wyk has presented a new formula for the calculation of viscosity of binary mixtures. I would point out that this problem has already been fully solved in two ways. On the base of thermodynamical considerations, the formula² has been found, where denotes the viscosity of the mixtures, m₁, ₁, m₂ and ₂ the mole fractions and viscosities of the two components, T the absolute temperature and q_m the molecular heat of solution. The latter may be also considered as the total change in energy caused by the interaction of both components. This change in the energy being rather difficult to determine experimentally, another method³ based on the association of the molecules has been chosen. It has been found that the simple formula of Arrhenius gives quite satisfactory results (as must be the case for ideal mixtures where no change in energy takes place), when for the calculation of mole fractions the physical molecular weights instead of the chemical molecular weights are taken into consideration. If S denotes the number of molecules of the component 2, which in the mixture are associated, the equations must hold. (In the quoted paper S has been defined as ” degree of solvation” ; it is better defined as ” degree of association”.)