ULTRACENTRIFUGAL STABILITY OF EMULSIONS 187 In conclusion, there appears to be no single universally applicable cri- terion for the quantitative characterization of the rate of demulsification, unless it were to be an actual specific reaction rate constant for the pro- cess, a parameter which cannot be unambiguously obtained from the present data without additional assumptions. It is therefore necessary to choose rather empirically that parameter which seems most likely to pro- vide useful data for the particular application. ACKNOWLEDGMENT The authors wish to express their appreciation to Miss Milagros Acevedo for her assistance in the preparation and ultracentrifugation of several of the emulsions and analysis of the solutions. (Received September 8, 1971) REFERENCES (1) Garrett, E. R., Stability of oil-in-water emulsi,ons, J. Pharm. Sci., 54, 1557-70 (1965). (2) Garrett, E. R., Prediction and evaluation of emulsion stability with ultracentrifugal stress, J. Soc. Cosmet. Chern., 21, 393-415 (1970). (3) King, A., and Mukherjee, L. N., The stability of emulsions. I. Soap-stabilized emul- sions, .l. Soc. Chem. Ind. (London), 58, 243 (1939). (4) King, A., Some factors governing the stability of oil-in-water emulsions, Trans. Fara- day Soc., 37, 168-80 (1941). (5) Beeher, P., Emulsions: Theory and Practice, Reinhold Publishing Co., New York, N.Y., 1965, Chap. 4. (6) Cockton, J. R., and Wynn, J. B., The use of surface active agents in pharmaceutical preparations: The evaluation of emulsifying power, J. Pharm. Pharmacol., 4, 959-71 (1952). (7) Void, R. D., and Groot, R. C., Parameters of emulsion stability, J. Soc. Cosmet. Chem., 14, 23344 (1963). (8) Vold, R. D., and Groot, R. C., An ultracentrifugal method for the quantitative determi- nation of emulsion stability, J. Phys. Chem., 66, 1969-75 (1962). (9) Vold, R. D., and Groot, R. C., The effect of electrolytes on the ultracentrifugal stability of emulsions, .I. Colloid Sci., 19, 384-98 (1964). (10) $chulman, J. H., $toeckenius, W., and Prince, L. M., Mechanism of formation and structure of micro emulsions by electron microscopy, J. Phys. Chem., 63, 1677-80 (1959). (11) Void, R. D., and Mittal, K. L., The effect of lauryl alcohol on the stability of oil-in- water emulsions, J. Coll. Inter]ace Sci., 38, 451-9 (1972). (12) Void, R. D., and Groot, R. C., The effect of varying centrifugal field and interfacial area on the ultracentrifugal stability of emulsions, ]. Phys. Chem., 68, 3477-84 (1964). (13) Ottewill, R. H., and Walker, T., The influence of non-ionic surface active agents on the stability of polystyrene latex dispersions, Kolloid-Z., 227, 108-16 (1968). (14) Brown, E.G., and Hayes, T. J., The absorptiometric determination of polyethylenegly- col mono-olcate, Analyst, 80, 755-67 (1955). (15) Weber, J. R., Degner, E. F., and Bahjat, K. S., Determination of nonionic ethylene oxide adduct in some commercial products, Anal. Chem., 36, 678-9 (1964).

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