THE STUDY OF SURFACE ANOMALIES OF FATTY SUBSTANCES 731 /•o• Figure 4.--Dilatometre (Dilatom- &re = Dilatometer Roda = Ground Montage = Set-up Pince = Clamp Vide = Vacuum Bois = Wood all dimensions in mm.). In the specific case under discussion, a crystalline skeleton might change in volume as a result of polymorphic modifications at constant tempera- tures, while the impregnating liquid apparently could remain at constant volume it can then be anticipated that certain strains and migrations will occur within the plastic solid. This concept suggested a study of the variations in volume of the solid fatty substance. Specifically, it seemed important to determine the time required for completion of the variations in volume, i.e., the polymorphic transformations. For this purpose, dilatometry at constant temperature was developed which makes it possible to analyze variations in volume due to polymorphism, to the exclusion of any phenomenon due to temperature variations. Surface defects appear readily at constant temperature. Temperature variations are not at all necessary, as has been claimed by certain authors. EX PERIMENTA L Dilatometry at Constan/ Temperature The procedure described here differs from the standard volumetric proc- esses of dilatometry because the latter always seek to reveal variations

732 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS in volume in the same direction, usually increases. In contrast, in the case described here, there can be either an increase or a decrease, and the variations to be measured are very slight. The apparatus (Fig. 4a) is filled as follows: The molten fatty substance is heated to 80øC. It is rapidly poured into a suppository mold and then cooled in the refrigerator. Seven suppositories are then inserted in the flask of the dilatometer and wedged. The dilatometer is next filled with mercury. The latter must be introduced under vacuum, using the setup recommended in Fig. 4b in order to expel air completely. Slight tapping often facilitates this filling. Mercury is introduced only up to the middle of the capillary tube. The filled dilatometer is then placed vertically in a thermostat held at 4-0.1øC (11). After less than half an hour, the temperature is finally stabilized, and the mercury level has risen in the capillary tube and is out- side the thermostatic bath. Graph paper is then attached to the capillary tube with cellophane adhesive tape so that the "zero" point of the scale is opposite the mercury level. Once this operation is completed, the flask can be left vertically or, preferably, tilted in the thermostatic tank to prevent any residual air from leaving the capillary and to collect it in the bend of the flask. It is then sufficient to record the displacement of the mercury level with time. These data can be graphed, using time as abscissa and displacement of the surface of the mercury in mm. (in relation to the zero point) as ordinate. To obtain relative variations of volume, it is only necessary to convert the ordinates expressed in min. by taking into account the diameter of the capillary and the volume of the suppository. To determine volume, a simple technique consists of weighing the mer- cury contained in a portion of the capillary tube. To determine the volume of the suppositories, it is sufficient to weigh a sample prepared with a product of known density, e.g., pure menthol (density -- 0.89). For the apparatus used here, which was equipped with uniform tubes, 103 mm. on the ordinate correspond to a 4% change in volume. Demonstration of Surface zfnomalies For visual examination and photography of surface defects, a lot of sup- positories identical to those inserted in the dilatometer is placed in hermeti- cally sealed powder boxes, at the rate of one per flask. All of the powder boxes and the dilatometer are placed simultaneously into the thermostat at constant temperature, and a powder box is sampled at given intervals for macroscopic and microscopic examin ation.