334 JOURNAL OF THE SOCIETY These examples indicate that the study of detergent effects in cos- metic preparations could be put on a more fundamental basis and that the current theories of detergency, although admittedly incomplete, could serve as a useful guide in such studies. A somewhat more com- plicated example is found in the emulsion creams. In using most creams the object is to spread a thin layer of the oily component on the skin and to use the aqueous com- ponent merely as a carrier. The problem of producing a satisfactory stable emulsion of good spreading properties has been thoroughly stud- ied. The behavior of such an emul- sion on contact with the skin, how- ever, is less well known. In many cases it is not known whether the emulsions break or remain stable on contact with skin and hair, although it is well known that contact with a foreign solid phase often causes emulsions to break. It has proved possible, in the case of metals and fabrics at least, to formulate emul- sions which will break as desired, with either the oil phase or the wa- ter phase clinging to the substrate. This could quite possibly be done in the case of cosmetic creams. The nature of the detergent or emulsify- ing agent is the major controlling factor in this phenomenon. Among the numerous products now avail- able it is probable that combinations can be found which will cause the emulsion to break in either manner or not to break at all. In shaving cream one of the essen- tial problems is the removal and OF COSMETIC CHEMISTS dispersion of the oily constituents which are added to increase the smoothness, lubricity, and emollient effect on the face. In this case a detergent of very high oil-dispers- ing power must be sought. This property must, of course, be cou- pled with the other well-known es- sential properties, but oil-dispersing power is relatively easy to measure and varies enormously among the different detergents. The synergy of various surface-active combina- tions with regard to emulsifying or oil-dispersing power has been em- phasized in several recent publica- tions, and some of these findings can doubtless be applied directly to the development of more rinsable shav- ing creams. Dentifrices present a problem which seems well suited to straightforward study of detergency. Here the nature of the substrate, tooth enamel, is well known and can even be simulated reasonably well by artificial mixtures. The na- ture of the soil, the so-called "den- tal plaque" is less well recognized, but .could probably be ascertained with no more than normal difficulty. The detergent must act in a diluted saliva medium, and it is known that the soil-substrate bond in this case is very strong. There is no doubt that a wide variation in tooth clean- ing power exists among the differ- ent individual detergents as well as among the different types. It is also possible that a systematic study of dental detergency would point the way toward an optimum tailor-made detergent, superior to

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.