Solidification curves and crystal spacings of binary fatty-acid mixtures.

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.