Largely by x-ray diffraction six crystalline states, I-VI, in order of increasing melting point, have been identified for cocoa butter. Of these states II, IV, V and VI are pure and identifiable with previously (or presently) identified polymorphs of 2-oleoylpalmitoyl stearin (POS), namely a-2, fl'-2, fi-3 ("V") and fl-3 ("VI"); V and VI representing distinct but very closely related crystalline structures. State I is a definite but fleeting and not readily characterized sub a state and may be a phase mixture, as state

Monoglyceride‐H2O systems in the range above about 5% H2O exhibit a varied phase behavior with a number of mesomorphic states reminiscent of those found for soap‐H2O systems. There are fluid neat, stiff and 舠short舡 viscous isotropic, and plastic or stringy middle states. In the case of saturated monoglycerides, neat states prevail at low molecular weight as with monolaurin, but viscous isotropic and finally middle states appear at higher chain length as with monoarchidin and monobehenin. The phase diagrams for systems of unsaturated compounds resemble those for systems of saturated compounds, with corresponding phase regions occurring at lower temperatures. The monoelaidin‐H2O system closely resembles a shifted monostearin‐H2O system, neither system showing middle. Middle phase appears in a small island for monoolein and monolinolein near 90C and 20% water. Water dissolves negligible amounts of monoglycerides so that phases which are nearly 100% H2O exist for substantially all systems and conditions when H2O content is 60% or more.

Summary In order to give a unified picture of recent findings on glyceride polymorphism a review is presented which covers in some detail the saturated single fatty acid triglycerides, the mixed C16−C18 saturated triglycerides, saturated diglycerides, and saturated monoglycerides. Mention is made, merely by way of comparison, of unsaturated and saturated‐unsaturated triglycerides and unsaturated diglycerides. The value of a knowledge of glyceride polymorphism in the identification of naturally occurring glycerides is indicated by a number of examples.

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Phase behavior of a homologous series of saturated even 1‐monoglycerides, starting with monomyristin, has been reviewed and their study extended to monoarachidin and monobehenin. The occurrence of sub α, α, β′ and β polymorphs was confirmed for all compounds, except in the case of β′ for monomyristin. It has been firmly established that there is a reversible sub α2 ⇄ sub α1 transition, (indicated by Malkin for monostearin) below the reversible sub α (sub α1)⇄α transition, for C18 through C22 compounds; it occurs at about 50 C and is apparently almost independent of chain length. The sub α2 to sub α1 transformation is particularly sensitive to impurity and disappears for 1‐monobehenin at about 10% 2‐monobehenin as produced by heating at 96 C. Heats of transformation are, for β′ and β crystal melting, about 50 cal/g; for α melting, about 35; for sub α → α transition, about 15 and for sub α2 to sub α1 transition about 3, which is several times as large as typical heats of melting of mesomorphic states. Diffraction data confirm the essential identity of all long spacing values and the occurrence of tilted chains for all polymorphs of a given compound. Much similarity is encountered between sub α and β′ patterns. Sub α2 and sub α1 are difficult to distinguish by diffraction pattern.