402 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Analytical Ultrace•ltri[ugation Tetradecane-Water-tgepal Co-610 oem ulsions A Beckman-Spinco Model E Analytical Ultracentrifuge equipped with a 4-cell An-F-Rotor was used. The equipment had been modified with timing devices and a motion picture assembly to permit repetitive photographs of centrifuging emulsions by transmitted light in each of four simultaneously centrifuged cells (25). Photographs of four simul- taneously ultracentrifuged emulsions were taken automatically at in- tervals down to 2 sec. The opaque emulsion separated on centrifugation into transparent layers of oil and water which were separated by a layer of opaque, con- centrated emulsion. The photographic film demonstrated sharp boundaries which changed with time as more oil was separated from the emulsion. Calculation of the rate of creaming and/or the rate of separation of oil from the emulsion was made by measurement of the photographs (magnification 2.2005) with a Nikkon Comparator,* read- {no, ttlroctl tn n n02 '•'" The A .......... r .... the top of air-oil, oil-emulsion, and emulsion-oil interfaces were measured. The volume corresponding to a length, L, in a 4 ø sector shaped cell is given by V -- (4/3{50) X = h(2L R,, d- L2) where R• is the distance from the center of rotation to the top of the cell and h is the thickness of the cell. The volume of separated oil was calculated from the distance between the air-oil and the oil-emulsion boundaries and could be expressed as per cent of total oil calculated from the assayed amounts of oil in the volume of emulsion added to the cell. A typical spray-prepared emulsion was found by analysis to contain 20.28 ml of tetradecane per 80 ml of 0.500{575 g/100 ml of aqueous surfactant solutions. Aliquots of 15 ml of emulsion were placed in 20-ml ampules through a l{5-gauge needle. The ampules were sealed and immersed in constant temperature water baths maintained at 2{5.0 ø, 35.0 ø, 45.0 ø, and 55.0 ø --+0.1øC. Ampules were removed at inter- vals, shaken lightly, and a sample of each was transferred to the ultra- centrifuge sector cell for ultracentrifugation. These emulsions were centrifuged sequentially at 10,589, 35,600, and 50,740 rpm. In addition, samples of this emulsion,were centrifuged at 40,000 rpm in a Beckman Model L preparative ultracentrifuge at 40øC for 8 hours. The three layers discernible were microscopically inspected. Nippon Koyaku K. K., Japan.

EMULSION STABILITY 403 Flotation Rate Studies of Toluene-G-2151-Water Emulsions Emulsions containing 50% toluene and 7% G-2151 surfactant were prepared by the Waring Blendor technique. Rates of creaming were photographically monitored in the analytical ultracentrifuge as a func- tion of various centrifugal speeds. Oil Separation Rates of Toluene-l% G-2151-Water Emulsions Samples of spray-prepared 50% O/W emulsion were placed in each of the cells of the 4-cell rotor and the oil separation rates of each were monitored photographically with their simultaneous ultracentrifuga- tion at 50,740 rpm. Samples of four identical spray-prepared emulsions (A, B. C, and D) were centrifuged at 50,740 rpm on the first and eleventh day after preparation. Four emulsions (E, F, G, and H), prepared at four different spraying pressures, were centrifuged in the 4-cell rotor at 50,740 rpm one day after preparation. RESULTS Analytical Ultracentrifugation o[ Tetradecane-Water-IgepaI Co-610 Emulsions The ultracentrifuged emulsion separates into transparent layers of oil and water separated by a layer of opaque concentrated emulsion, the cream. The per cent oil separated was plotted as a function of time of ultracentrifugation. Typical plots are given in Fig. 2 for emulsions __ 50740 R PM • 35,600 R PM . .• •e•. • • // / •,•9 R P M I •1'•* •• 0 45 • o•*-•* • •o ,•o ,• • •¾• •oo Time in I0 $ Second• Figure 2. Volume per cent of oil separated as monitored frotn photographs rs. time of ul- tracentrifugation at various sequential rpm values. The tetradecane-water emulsions with 5% surfactant, Igepal Co-610, were aged for 11 days