COSMETIC FUNCTIONS OF SYNTHETIC DETERGENTS 335 the present products which were developed for general use rather than for specific use in dentifrices. Such a program would require close co-operation among a group of specialists, and would doubtless be costly, but the chances for improve- ment over even the more recent formulas would be significant. In conclusion the following points may be summarized and empha- sized: 1. The synthetic chemistry of detergents has advanced to a point where numerous different types and their various generic properties are well recognized. Not only are hundreds of individual products known, but the possibility exists for synthesizing or formulating in- numerable others with reasonably good chances of predicting their properties. 2. The physico-chemical princi- ples underlying detergency, wet- ting, emulsification, and other phases of surface activity are suf- ficiently well understood so that individual problems can be soundly analyzed and need not be attacked solely by laborious empirical meth- ods. 3. The organic and physical branches of the science of deter- gency are already being successfully combined and applied in textile processing, metal cleaning, launder- ing, and other branches of technol- ogy. 4. Although the limitations im- posed by the sensitive and living nature of the human skin are se- vere, it is highly probable that a similar intensive application of the newly developed science of deter- gents to cosmetology would result in corresponding advances. In fact, these very limitations make the scientific approach, and the utiliza- tion of the fundamental knowledge now available, much more attrac- tive than the purely empirical ap- proach.

SURFACE-ACTIVE AGENTS IN THE COSMETIC INDUSTRY* By FOSTER DEE SNELL and IRVING R•.ICU Foster D. Snell, Inc., New York, N.Y. IN SOME RESPECZS AN ex- cursion into the realm of surface activity is like going with Alice into Never-Never Land, where up is down and down is up. More often it is an application by sound logic of familiar physico-chemical prin- ciples. SURFACE CHEMISTRY The formulation of cosmetics de- pends largely on the chemistry of surface forces and phenomena. In most such products, one phase has to be uniformly and permanently dispersed in another. Whether the particles dealt with are of colloidal size or are much larger the principles of colloid chemistry are those which apply. Classical colloid chemistry is the study of special properties of sub- stances which have been dispersed to the colloidal range. Such par- ticles are intermediate in size be- tween those in molecular solution and those just visible in an ordinary microscope. Surface chemistry is the study of interfacial phenomena, and as such it provides a theoret?cal * Presented at the May 20, 1949, Meeting, New York City. background for the behavior of col- loidal systems, and for the behavior of many other systems which are not ordinarily considere4 colloidal. However in general usage, the term colloid chemistry is often used as a synonym for surface chemistry. Suspensions of fine particles in liquids, as in liquid make-up or toothpaste, are frequently not of colloidal fineness. Nevertheless the specific interfacial area is great enough for surface effects to become important. Other types of systems with large interfacial areas are powders, emulsions, foams, and mists. Most cosmetic products either exist in one of these forms or are converted to one of them in use. IMPORTANCE OF SURFACE CHEM- ISTRY IN COSMETIC SCIENCE Considerations of surface chem- istry become important when large specific surface areas are involved. In applying cosmetic products to the skin or hair, usually a small amount of product must cover a large area. This introduces con- siderations of wetting and adhesive forces between the cosmetic and the 336