T HE TERM morphology is used to denote the general relation of the physical behavior and performance of fats, oils, and shortenings to their crystal structure and the molecular configuration of their triglyeeride components. This report deals with the crystal transformations which occur in various common fats, the physical changes which take place during crystallization, tempering, and subsequent storage under different conditions, mid the effects of this polymorphie behavior on the performance of commercial fats in certain shortening applications.The subsequent discussion is based on the results of an extensive study of five individual triglycerides and numerous samples of common commercial fats, including various types of ordinary lard and hydrogenated lard, rearranged lard, tallow (beef), hydrogenated cottonseed and soybean oils of different iodine values, and the flakes of all these types of fats. The various crystal modifications it, which fats exist and the sequence of polymorphie transforlnations which they undergo were determined by correlating tbeir x-ray diffraction patterns with information obtained from cooling and heating curves under various (,xperimental conditions, from solubility determinalions in several organic solvents, and from observations by means of polarized-light nlicroscopy under carefully-controlled conditions. The Imrformancc of shortenings is dismlssc(1 in terms of the l)hysical cbara(~t~,ristics of the w~rious crystal nm(lifications in which they have been found to exist.

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Summary The effect of water on the solidification points of the normal saturated fatty acids from caproic to stearic, inclusive, has been investigated, and the depressions caused by given amounts of water in each of these acids has been presented. The solubility of water in six of the acids above their solidification points has been determined, and these data have been reported, together with rough approximations of the solubility of water in the other acids of this series.

Oleic and linoleic acids were prepared by combination of crystallization and distillation procedures, giving careful consideration to the problems involved in the removal of the naturally occurring impurities. The solubilities of these highly purified acids were determined in a variety of common organic solvents over wide ranges of temperature and concentration. Factors influencing the solubility were evaluated by comparing the curves in different solvents on a molecularly equivalent basis. It was found that the fundamental solubility behavior of oleic and linoleic acids differs little from that of stearic acid. The internal pressures, polarities, molar volumes, hydrogen-bonding tendencies, and heats of fusion estimated from the slopes of the solubility curves of oleic and linoleic acid are consistent with the values calculated from other observations.

The contribution that x‐ray diffraction has made to the understanding of triglyceride polymorphism is reviewed. The crystal structure of these compounds is explained in terms of molecular orientation in the crystal lattices. At the present time only the crystal structure of the monoacid saturated triglycerides has been reasonably well defined. Mixed triglycerides and mixtures thereof have not yet been fully investigated. This review stresses the need for systematic correlation of the crystal structure of fats with the molecular composition and configuration.