THE STUDY OF SURFACE ANOMALIES OF FATTY SUBSTANCES 729 Figure 1.--Surface of suppository with Figure 2.--Suppository with white surface crystallized caffeine (12X). mold (12X). Figure &--Suppository with gray surface mold (12X). These defects are also more likely in the presence of small quantities ot very finely powdered substances in dispersion in the fatty phase. Under these various conditions, defects appear rapidly and abundantly. Surface anomalies of this type appear to be due to changes in crystalline structure however, is just one or are several phenomena involved? Chocolate bloom has been the subject of considerable research (1-6), and a general review by Andersson (7) summarizes the theories of these authors. Not only were theories formulated, but remedies were proposed and solutions were found which considerably diminish chocolate bloom. Today good quality chocolate remains bright at 25øC and forms no bloom,

730 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS due to the heat treatment of"tempering." According to Andersson, "it is a question of directing crystallization through a rational process of tempering and cooling in order to get the fat phase to solidify inside the chocolate paste in the stable crystalline •-form (7). This treatment is rather lengthy and is performed on chocolate poured in a pasty state into molds placed on vibrators. The method seems difficult to apply to suppositories in pharmaceutical laboratories, because fatty substances are poured in a fluid state and tempering chambers are not available. Detailed examination of the different forms of "bloom" makes it possible to demonstrate the different reasons for these phenomena and perhaps sug- gest an effective remedy. It is, however, useful to review first some basic concepts about the crystallography of the fatty substance and the physical state of solid fatty substances and to specify what is meant by "change of volume." Crysta#ography of Fatty Substances Triglycerides exist in different polymorphous forms. For the sake of simplicity, it is reasonable to agree with Lutton (8)--to the exclusion of any other theory--that there are three polymorphous forms, designated by the symbols, a, •' and •, listing them in the order of rising melting points, rising stabilities and rising densities. When a triglyceride is melted at temperatures above 70øC and then suddenly cooled, a so-called "tempered" fatty substance is obtained, the crystals of which are in the a-form. The latter can change rather rapidly to give the •'-form and then far more slowly to yield the •-form. It is then said that the fatty substance is "tempered." It should be noted in particular that, at a given temperature, the most stable form has a higher density than the others. Physical State of Solid Fatty Substances Although it is generally considered that a suppository mass passes di- rectly from the solid state to the molten state, this is not entirely true. Cocoa butter can be considered entirely liquid at 40øC. It is then neces- sary to cool it to a low temperature (generally below 0øC) to be certain that it is composed entirely of solid crystals. Between these limits, e.g., at 25øC, cocoa butter should be regarded as a "plastic solid," i.e., it con- sists of crystals impregnated with a liquid phase. The solid crystals are not separated from each other but constitute a skeleton like felt. The inter- stitial liquid also serves as solvent of part of some of the solid components. The relative proportions of solid crystals and liquid phase at different temperatures can be studied directly by dilatometry or evaluated indi- rectly by measurement of consistency, e.g., by means of micropenetrom- etry with a falling needle (9, 10).