Solidification Curves and Crystal Spacings of Binary Fatty-acid Mixtures

Abstract

THE solidification curves of binary systems formed by adjacent even-numbered saturated fatty acids show, besides a minimum at about 73 mol. per cent of the lower-melting acid, an inflexion at the equimolar composition. To explain this departure from the Roozeboom classification of solid solutions¹, various investigators have assumed the formation of a compound by the two components of the system², an obvious assumption in view of the tendency of fatty acids towards association established by Robertson's cryoscopic studies³. However, compound formation has not been adequately verified by the results of X-ray measurements of fatty-acid mixtures, and Slagle and Ott⁴, having found only one long crystal spacing d₁ instead of two d₁ spacings in mixtures other than equimolar, suggested a continuous series of solid solutions. The peculiar shape of the solidification curves of fatty acids was attributed by them to polymorphism.