ULTRACENTRIFUGAL STABILITY OF EMULSIONS 179 tion. This difference in behavior may be due to the smaller drop size presumably achieved by direct emulsification in the presence of the higher concentration of surfactant. 50% Nujol-50% water-Tween 20 emulsions containing initially 0.15 to 0.35% Tween 20 on the basis of the aqueous phase separated oil in the ultracentrifuge following curves showing regions I and III-A. Above 0.35%, where oil separates only very slowly, the empirical equation was no longer obeyed and the curve consisted of regions I and III-B. With 50% Nujol-50% water emulsions stabilized with Triton X-100 at 0.1% Triton on the basis of the aqueous phase, the curve of oil sepa- rated rs. time of ultracentrifugation consisted of regions I and III-A. At higher concentrations (0.15 to 0.4%), only regions I and III-B were observed. Nujol-water emulsions stabilized with 0.1% CPC gave a curve (Fig. 3) showing only regions I and III-B, resembling in type of behavior those stabilized with 0.2% Triton X-100. 50% olive oil-50% water-0.2% SDS emulsions gave curves of oil separated vs. time showing regions ! and III-A. However, when such emulsions were prepared by direct mixing with 0.4% SDS there was an induction period before any oil separated, and then it separated accord- ing to I and III-B. To facilitate quantitative comparison of the behavior of the differ- ent systems, the per cent oil separated after various times and the param- eters of the empirical equation (extrapolated maximum % oil separable and b) where applicable are given in Table I. Table II presents the ob- Table I Dependence of Per Cent Oil Separated from 50% Oil-Water Emulsions on Oil and Emulsifier Oil Separated After t Min (%) Oil .... Emulsion 25 75 100 (%) b X 10 • min -! Nujol-water-0.2 % SDS" Nujol-water-0.2% Tween 20 b Nujol-water-0.2% Triton X-100c Olive oil-water-0.2% SDS a Nujol-water-0.1% CPC e 23.6 42.8 52.4 91.6 21.9 26.1 27.6 29.5 4.2 8.1 9.5 ... 29.3 41.6 ... 52.1 17.5 27.4 31.5 ... Emulsions M 111968. Emulsions A 091069. Emulsions A 090969ß Emulsions M 060669. Emulsions A 112669.

180 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS served rate of separation of oil after varying periods of centrifugation and Table III a15ter separation ot5 various constant 15ractions of the oil present. Table II Rate of Oil Separation from 50% Oil-Water Emulsions % Oil/Min After t Minutes Emulsion 25 50 75 100 Nujol-water-0.2% SDS• 0.53 0.53 Nujol-water-0.2% Tween 20 b 0.21 0.068 Nujol-water-0.2% Triton X-100 c 0.09 0.07 Olive oil-water-0.2% SDS a 0.51 0.20 Nujol-water-0.1% CPC • 0.24 0.17 0.53 0.53 0.033 0.020 0.047 0.030 0.11 0.07 0.16 0.15 Emulsions M 111968. Emulsions A 091069. Emulsions A 090969. Emulsions M 060669. Emulsions A 112669. Table III Rate of Oil Separation from 50% Oil-Water Emulsions (Per Cent/Minute) Amount of Oil Separated (%) Emulsion 10 20 30 Nujol-water-0.2 % SDS• ... Nujol-water-0.15% Tween 20• 3.0 Nujol-water-0.12 % Triton X-100 c 0.13 0.53 1.2 0.01 0.53 0.24 . . . Emulsions M 111968: Emulsions A 091069. Emulsions M 111969 TR. DISCUSSION As is evident from the experimental results, in most cases the rate of separation o15 oil decreased with time of ultracentrifugation, in many cases following the empirical equation developed to describe the be- havior of olive oil-water-SDS emulsions (11). According to this relation, t 1 t - + % oil..• b. % Oilm=,• % Oilm=,•