THE STUDY OF SURFACE ANOMALIES OF FATTY SUBSTANCES 733 Determinalion of Favorable Temperalure To show up surface defects, if any, as soon as possible, it is necessary to combine a number of favorable conditions: (a) First, the substance must be a "plastic solid" cocoa butter is plastic at a temperature of 25øC and Suppocire A* at a temperature between 25 and 29øC. (b) A second condition is the introduction of very fine carbon black into the molten fatty substance. (c) In other cases, mixtures of fatty substances can be prepared which are intended solely to promote the appearance of surface defects. RESULTS AND DISCUSSION (a) After different orientation tests, suppositories were prepared from the following mixture: Codex cocoa butter* ...................................... 100 g. Printex U carbon black* ................................... 7 g. The graph representing dilatometry at constant temperature is shown in Fig. 5. It is to be noted that the decrease in volume reaches 4%. A very Figure 5.--Dilatometric curve (beurre de cacao = cocoa butter noir de carbone = carbon black heures = hours diminution du volume en % = % contraction of volume). long period is necessary to attain this maximum decrease, since observa- tions are spread over a month and a half. With other suppository formulas or other experimental conditions, the form of the graph at the beginning of the experiment may be different. But in all cases, after a little time, the process follows a constant course, and the ends of all curves are identical * Cf. Appendix I.

734 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS and correspond to a common mathematical expression. This makes it possible to estimate the limit to be reached by the decrease in volume with- out waiting for the end of the experiment. For example, on Fig. 5, it would have been possible after the 3rd day to estimate the limit of contraction, although it was not reached until the end of 40 days. The principle of this method of measurement is set forth in Appendix II. (b) Macroscopic and microscopic examination of samples was made at the same time as the dilatometric data were obtained. The arrows on Fig. $ indicate the times samples were taken. The latter were examined in flat Figure &--Freshly prepared suppository smooth surface the scratches are due to imperfections of the aluminum molds (12X). Figure 8. Suppository after 20 hours de- velopment of stirface defects (12X). Figure 7.---Suppository after 3 hours begin- ning of stirface defects (12X). * Cf. Appendix I Figure 9.--Suppository after 20 hours the surface (tefects in this sample are caused by modifications of the surface due to improper handling (12X).