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.

J. Soc. Cosmetic Chemists, 19, 699-706 (Sept. 16, 1968) A Quantitative Study of the Effect of Depilatory Solutions Upon Hair HARVEY ALLEN YABLONSKY, Ph.D., and ROBERTA WILLIAMS, B.S.* Synopsis--A procedure is described for determining the efficacy of depilatories. It involves the measurement of two parameters, the mean initial cross-sectional hair diameter and the time of maximum hair swelling. Plots of both the length and the width of swelling hair vs. time are sigmoid. The t•vo curves are sequential, the longitudinal sigmoid curve commencing on termination •f the cross-sec- tional one. Neither the time of occurrence, nor any other parameter ooe the sigmoid curve appears correlated to hair-break time. Seemingly identical hairs, in identical soluti{ms, show breaking times which vary from less than one hour to more than ten days. It is shown that slope maxima of the sigmoid curves may be used to define an in vitro index ooe depilatory effectiveness. INTRODUCTION The practice of hair removal for cosmetic purposes is an ancient one. Records of recipes for hair epilation and depilation date back as far as 1500 B.C. (1). Methods of attaining this end run the gamut from physically tearing the hair by its root to the application in an acceptable cosmetic base of disulfide bond-cleavers. Brute force methods of hair removal are usually dependent upon the imbedding or attachment of the undesired hair to a matrix which is first applied to the skin. Both the matrix and incorporated hair are then "painlessly" removed by tearing from the skin (2-5). Due to the questionable painlessness o[ this pro- cess, epilatories have, in this country, been largely superseded by them- * Bristol-Myers Products, Physical Chemistry Dept., Research Laborat•rics, 135{) Liberty Ave., Hillside, N.J. 07207. 699