090 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS theory advanced by Davies (10). The emulsion droplet size distribution was also influenced by the initial surfactant location. Placing of the hydrophilic surfactant in the aqueous phase favored formation of emul- sions having smaller droplets than the emulsions formed by placing all surfactants in the oil phase. The effect of initial surfactant locations on emulsion stability was also significant. Due to the complexity of the nature of emulsions, it is difficult to generalize the results beyond the scope of the experiments. It is prob- able, however, the initial surfactant location plays an important role in determining the characteristics of many practical emulsions. Particu- larly, if the systems are such that the rate of surfactant migration is slow, the initial surfactant location may be an important consideration from the manufacturing viewpoint. The optimum initial surfactant location for a given system would be dependent on the end results de- sired. For example, if the final emulsion should be a W/O emulsion but the phase volume is such that an Of W emulsion can be formed, it would probably be best to place all the surfactants in the oil phase to avoid phase inversion. On the other hand, if it is desired to produce an O/W emulsion having finest droplet size, it may be better to place all the surfactants in the aqueous phase. If the surfactant migration from one phase to another can produce viscosity change and if such a change is un- desirable from the product viewpoint, it may be best to distribute the surfactants according to their solubility in each phase prior to emulsifica- tion. ACKNOWLEDGMENT The author gratefully acknowledges the assistance of John C. Lambrechts in collecting the experimental data and the assistance of William E. Gardner of Sloan Research Industries in preparing micro- photographs. (Received December 8, 1967) REFERENCES (1) Beeher, P., Emulsions: Theory and Practice, 2nd ed., Reinhold Publishing Corp., New York, 1965, pp. 267-325. (2) Sumner, C. G., Clayton's Theory of Emulsion and Their Technical Treatment, 5th ed., Chemical Publishing Co., New York, 1954, pp. 480-528. (3) Stanko, G. L., Fiedler, W. C., and Sperandio, G. J., The effect of physical factors on the formation of cosmetic emulsions, J. Soc. Cosmetic Chemists, 5, 29-50 (1954).

EFFECT OF SURFACTANT LOCATION ON EMULSIONS 697 (4) Benson, F. R., Griffin, W. C., and Truax, H. M., Statistical approach to common variables in emulsion preparation, Ibid., 13, 437-48 (1962). (5) Osipow, L. E., Sinface Chemistry, Theory and Industrial Applications, Reinhold Pub- lishing Corp., New York, 1962, pp. 305-9. (6) Sherman, P., The Influence of Emulsifier Concentration on the Rheological Properties of Emulsions, in Sherman, P., Rheology of Emulsions, The MacMillan Co., New York, 1963, pp. 73-90. (7) Becher, P., Emulsions: Theory and Practice, 2nd ed., Reinhold Publishing Corp., New York, 1965, pp. 59-85. (8) Sherman, P., Factors influencing emulsion viscosity and stability, Research (London), 8, 396-401 (1955). (9) Becher, P., The effect of the nature of the emulsifying agent on emulsion inversion, _f. Soc. Cosmetic Chemists, 9, 141-8 (1958). (10) Davies, J. T., and Rideal, E. K., Interfacia! Phenomena, Academic Press, New York, 1963, pp. 366-83. (11) Bancroft, W. D., The theory of emulsification, J. Phys. Chem., 17, 501-19 (1913). (12) Addison, C. C., The measurement of surface and interfacial tension at fresh surface by the vibrating jet method, Phil. Mag., 36, 73-100 (1945). (13) Rideal, E. K., and Southerland, K. L., The variation of the surface tension of solution with time, Trans. Faraday Sot., 48, 1109-23 (1952). (14) Schwartz, A.M., and Perry, J. W., Surface Active Agents: Their Chemistry and Tech- nology, Vol. 1, Interscience, New York, 1943, pp. 286-8. (15) Davies, J. T., A quantitative kinetic theory of emulsion type, I. Physical chemistry of the emulsifying agent. Proc. Intern. Congr. Surface Activity, 2nd, London, 1957, 1, 426-38. (16) Griffin, W. C., Classification of surface-active agents by "HLB," _f. Soc. Cosmetic Chemists, 1, 311-26 (1949). (17) Griffin, W. C., Calculation of HLB values of nonionic surfactants, Ibid., 5, 249-56 (1954). (18) Griffin, W. C., Ranauto, H. J., and Adams, A.D., Further studies on emulsion systems, Am. Perfumer Cos•etics, 81, 31-42, (Sept., 1966). (19) Guide to the Use of Atlas Surfactants and Sorbito! in Cosmetic and Pharmaceutica! Products, Atlas Chemical Industries, Wilmington, Del., 1965, p. 40.