44 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS .. :•,,.• o .• '•' .. •. , / • ? • ' " ß • -0 •" •:'% 0 • ? • • ' '• ....... •.•. .•'.'• ...... •:• -:-:• ..... • • 0.': •'•: . * •-' ::'• -:'-: ' Fig. l.•Photomicrograph of Emulsion No. 1 showing high percentage of smallest particles. As subsequent experimentation and measurements showed, the emulsion having the best properties and highest degree of stability did not show an appreciable difference in particle size distribution from the other products and we are reluctant to draw any definite conclusions from this phase of the work. After the measurements were completed, each emulsion was shaken and completely dispersed, and one hundred cc. was measured out in a cylindrical graduate and allowed to stand at room temperature. Another bottle of the emulsion was kept under the same conditions and these prod- ucts were observed regularly for evidence of change of any nature. The only noticeable changes were, of course, the creaming of the products. A considerable difference in the rate of creaming became apparent almost immediately, and the time required for each emulsion to complete its creaming was determined. These times varied from 72 hours to one week. The rates of creaming differed also in that emulsion No. 3 showed an almost immediate creaming while emulsion No. 2 showed none until 20 hours later. For comparative purposes, photographs of the emulsions at the start and finish of creaming are shown in Figs. 4 and 5. It is very apparent that the method of making an emulsion affects both

FACTORS ON THE FORMATION OF COSMETIC EMULSIONS 45 its rate of creaming and the amount of creaming and assuming that cream- ing is indicative of stability to some extent, we are able to recommend one method as preferable to others. At the end of 60 days, after being allowed to stand at room temperature without handling or agitation, the e .mulsions were redispersed and the physical properties were again measured. The changes in surface tension, specific gravity, and pH for all of the samples were not significant, varying only a fraction of a per cent if at all. More pronounced changes in viscosity were noticed, ranging from an increase of .9 cps to a decrease of 4.3 cps. The emulsions were then shaken up and rated according to the ease with which they were redispersed, and a panel of pharmacists was asked to evaluate each product on its general appear- ance. These ratings are all tabulated in Table 3, which gives an over-all picture of the emulsions studied. Of the emulsions prepared and studied, Product No. 2 seemed superior in most respects and, from the table, it can be seen that this emulsion rates the highest on all comparisons except particle size distribution and there it ranked second in our arbitrary classification. On the basis of these comparisons, therefore, the following general statements are proposed for consideration: