TERMINOLOGY OF EMULSION BEHAVIOR 823 may not represent the rate of coalescence. This is plausible, if the rate of transport of the coalesced drops--from the site of coalescence--is the slowest step in the overall kinetics of the separation of the disperse phase. CONCLUSION It is hoped that the present communication will be helpful in under- standing the underlying ideas and the implications of various forms of emulsion instability. A few important points are recapitulated: 1. The term "coagulation" should not be used to describe emulsion behavior because it causes unnecessary misunderstanding. Its use should be restricted to sols only. 2. The terms creaming, flocculation, coalescence, and demulsifica- tion or breaking should be used judiciously and with discernment. 3. The use of unwarranted terminology should be avoided. 4. The property of the system measured as an index of emulsion in- stability should be mentioned explicitly. This is very important be- cause different information and conclusions regarding emulsion insta- bility are possible, depending npon the criterion chosen (9). ACKNOWLEDGMENT The author wishes to thank Dr. R. D. Vold, University of Southern California, for his constructive criticism and helpful suggestions. (Received November 9, 1970) (1) (2) (3) (4) (5) (6) (7) (8) (9) 00) REFERENCES Ecanow, B., et al., New aspects of suspension theory, A,ner. Per/urn. Cosmet., 84, 27-30 (1969). Becher, P., Emulsions: Theory and Practice, 2nd Ed., Reinhold Publishing Corp., New York, 1965, pp. 154, 170, 2. Sherman, P., Emulsion Science, Academic Press, New York, 1968, p. 78. Van den Tempel, M., Stability of oil-in-water emulsions. II. Mechanism of the coagula- tion of an emulsion, Rec. Tray. Chim., 72, 433-61 (1953). Lawrence, A. S.C., The breaking of oil emulsions with synthetic detergents, Chem. Ind. (London), 615-7 (1948). Rehfeld, S. J., Stability of emulsions to ultracentrifugation: Discontinuity at the criti- cal micelle concentration, J. Phys. Chem., 66, 1966-8 (1962). Garrett, E. R., Prediction of stability in phar•naceutical preparation. VIII. Oil in water emulsion stability in the analytical ultracentrifuge, ]. Pharm. Sci., 51, 35-42 (1962). Vold, R. D., and Groot, R. C., Parameters of emulsion stability, J. Soc. Cosmet. Chem., 14, 233-44 (1963). Mittal, K. L., Factors influencing the ultracentrifugal stability of oil-in-water emulsions, Ph.D. dissertation, University of Southern California, June, 1970. La Mer, V. K., Coagulation Symposium, ]. Colloid Sci., 19, 291-3 (1964).

824 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS (11) Wilson, R., and Ecanow, B., Powdered particle interactions: Suspension fiocculation and caking, I, J. Pharm. Sci., 52, 757-62 (1963). (12) Ecanow, B., and Wilson, R., Powdered particle interactions: Suspension flocculation and caking, II, Ibid., 52, 1031-8 (1963). (13) Ries, H., and Meyers, B., Flocculation mechanism: Charge neutralization and bridging, Science, 160, 1449-50 (1968). (14) Matthews, B., and Rhodes, C., Coagulation and flocculation in the suspensions of griseofulvin and polystyrene latex, J. Pharm. Pharmacol., 20, 204S-12S (1968). (15) La Met, V. K., and Healy, T. W., The role of filtration in investigating flocculation and redispersion of colloidal dispersions, J. Phys. ½hem., 67, 2417-20 (1963). (16) Wilson, R., and Ecanow, B., Powdered particle interactions: Suspension flocculation and caking, III, J. Pharm. Sci., 5•1 782-6 (1964). (17) Van den Tempel, M., Coagulation of oil-in-water emulsions, Proc. Int. Congr. Surface Activ., 2rid, London, I, 439-46 (1957). (18) Vold, R. D., and Groot, R. C., An ultracentrifugal method for the quantitative determi- nation of emulsion stability, J. Phys. Chera., 66, 1969-75 (1962).