Pippard relations and critical phenomena in binary liquid mixtures

The cylindrical approximation originally proposed by Pippard for the λ-transitions in one-component systems is extended to multicomponent systems. The application of the generalised Pippard relations to binary liquid mixtures is considered. The relations for He³ + He⁴ mixtures are shown to be equivalent to those obtained by earlier workers. The validity of the relation relating specific heat and thermal expansion for binary liquid systems is discussed on the basis of the measurements performed on the system methaonl +n-heptane. Lack of information on the behaviour of a few quantities prevents a quantitative test of the relation.