346 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS (2) McBain, J. W., "Colloid Science," Boston, D.C. Heath and Co. (1950). Kruyt, H. R., "Colloid Science," Vol. I, Amsterdam, Elsevier Press (1952), p. 340. (3) Gurwitsch, L., "Wissenschaftliche Grundlagen der Erdolbearbeitung," London, Transla- tion by Moore, Chapman and Hall (1932), p. 430. (4) Raschevsky, N., Z. Physik, 46, 568 (1928). (5) Stackelberg, M. v., Klockner, E., and Mohrhauer, P., Kolloidzschr., 115, 53 (1949). (6) Davies, J. T., and Haydon, D. A., Proc. 2rid Intern. Congress Surface •tctivity, Butter- worths, London 1, 417 476 (1957). (7) Davies, J. T. and Rideal, E. K., "Interfacial Phenomena," New York, Academic Press, Inc. (1961). (8) McBain, J. W., and Woo, T. M., Proc. Roy. Soc. (London), 163A, 182 (1937). Kaminski, A., and McBain, J. W., Ibid., 198A, 447 (1949). (9) Haydon, D. A., Nature, 176, 839 (1955). Lewis, J. B., and Pratt, H. R. C., Ibid., 171, 1155 (1953). (10) Pospelova, K. A., and Rehbinder, P. A., •tcta physicochima. U.R.S.S., 16, 71 (1942). (11) van der Waarden, M., •7. ColloidSci.,7, 140 (1952). (12) Ilkovid, I., Collection tray. chim. tch•coslov., 4, 480 (1932). (13) Langmuir, I., Cold Spring Harbor Symposium, 6, 193 (1938). (14) Cockbain, E.G., and Schulman, J. H., Trans. Faraday Soc., 36, 651 (1940). (15) Matalon, R., Ibid., 46, 674 (1950). (16) Kaminski, A., and McBain, J. W., Proc. Roy. Soc. (London), 198A, 447 (1949). (17) Davies, J. T., Bell, G., and Law, P. J. S., Research Project in Dept. of Chemical Engineering, Cambridge (1960). (18) Hartung, H. A., and Rice, O.K., 5•. Colloid Sci., 10, 436 (1953). A SURVEY OF DR. J. T. DAVIES' CONTRIBUTIONS TO EMULSION STABILITY, FOAM STABILITY AND OLFACTORY THRESHOLDS OF ODORANTS T•E s'rut)•Es of J. T. Davies have contributed very significantly to the understanding of several phenomena highly important to cosmetic chemists. His recent work has led to the development of equations for predicting emulsion stability, foam stability and olfactory thresholds of odorants. Earlier workers had shown that an electrical charge an a monolayer might bring about radical changes in its free energy and surface tension. As early as 1951 (1), as a result of his extensive studies of interfacial po- tentials and reactions, Davies had shown that surface potentials (2) and the amounts and rates of adsorption (4) are also affected by the electrical charge, and had developed an equation of state for oil-water films. In 1956 (8) he developed a similar expression to cover charged monolayers at the air-water interface. In 1957 (10) Davies reported data, obtained by using a new viscous- traction surface viscometer of his own design, which showed a correlation between foam stability and surface viscosity. In the same year he evolved a quantitative kinetic theory of emulsion type, which provided a firm basis for the HLB system of classifying emulsifiers (11). The HLB num- ber was shown to depend upon the ratio of the coalescence rate of the oil-in-

THE SEVENTH SPECIAL AWARD 347 water emulsion to that of the water-in-oil emulsion. The HLB value of an emulsifier was shown to be calculable from the chemical formula by sum- ming up the group numbers for the various hydrophilic and hydrophobic groups in the molecule to obtain a net value. Additional studies on interfacial viscosities of monolayers at the oil- water interface were reported in 1959 (13). These studies confirmed earlier suggestions that high interfacial viscosity is correlated with high emulsion stability. Emulsification and general cosmetic problems were examined as early as 1952 (3) (from a thermodynamic and kinetic viewpoint), and the phe- nora enon of spontaneous emulsification was further investigated in 1957 (12). In the field of olfaction (5), Davies suggested in 1953 that a limiting factor in the production of olfactory sensation by any odorant was the ability of the odorant to penetrate and puncture the bimolecular lipid layer of the olfactory cell membrane. With Taylor (6, 7), he reported in 1954 on measurements of the effectiveness of various odorants in ac- celerating the hemolysis of red blood cells by saponin. The red cell was a convenient substitute for the olfactory cell and was believed to possess a membrane of similar type, wherefore penetrating power should be similar in the two cases. The logarithms of accelerating potencies of the odorants on red cell hemolysis were shown to be inversely proportional to the log- arithms of their olfactory thresholds. In other words, the odorants de- tectable in the highest dilution also exerted the greatest effect upon penetra- tion of the cell membrane. In 1957 Davies (9) reported a correlation between olfactory thresholds and free energy of adsorption at the oil-water interface. Molecular size and shape of odorants were held to be factors in influencing the dislocation produced in the olfactory membrane. An equation also was derived for predicting olfactory thresholds from hemolytic accelarating power and molecular volume and shape. Much of the work quoted above is included in the book Interfacial Phenomena, by J. T. Davies and E. K. Rideal, Academic Press (1961). SELECTED BIBLIOGRAPHY REFERENCES (1) Davies, J. T., "Distribution of Ions Under a Charged Monolayer--Surface Equation of State for Charged a Film," Proc. Roy. Soc., 208A, 224 (1951). (2) Davies, J. T., "Measurement of Contact Potentials at Oil-Water Interface," Nature, 167, 193 (1951). (3) Davies, J. T., "Surface Chemistry and Its Application to Emulsion and Cosmetic Prob- lems," Perfumery Essent. Oil Record, 43, 338 (1952). (4) Davies, J. T., "Application of Gibbs Equation to Charged Monolayers and Their Desorp- tion from the Oil-Water Interface," Trans. Faraday Soc., 48, 1052 (1952). (5) Davies, J. T., "Odor and Morphology of Molecules," Ind. de la Perfumerie, 8, 74 (1953). (6) Davies, J. T., "Odor and Morphology of Molecules," Ind. de la Perfumerie, 8, 74 (1953). Nature, 174, 693 (1954).