SURFACE-ACTIVE AGENTS will be wasted in useless processing or in useless raw materials. An interesting aspect of pigments in powders, lipsticks, and other pig- mented cosmetics, is that their coloring power increases as they are made finer--up to a certain point-- whether subdivision is caused by grinding or by deflocculation. This is true only within limits. Beyond the limit of fine particle size, the coloring power decreases. Particles which are substantially smaller than the wave length of light have no color. Related to this is the fact that the whiteness of an emulsion is con- trolled by particle size. If an emul- sion is quite coarse, it will be grayish and translucent. As the particle size is made smaller, it will become whiter and more opaque, since more surfaces at which light can be re- flected and diffracted are created. However, if the particle size becomes too small, the emulsion will lose whiteness and opacity. The ex- treme example is a colloidal sol which, like a solubilized liquid, is transparent to transmitted light. Usually the problem is that the particles are too coarse rather than too fine. So proper milling and de- fiocculation of such products as lip rouge is important, not only to ob- tain a uniform product, but to ob- tain maximum color. Variations in particle size cause differences in shade. Deflocculation may be important for several reasons. If it is desired to suspend a powder in a liquid, as in calamine lotion or some liquid IN COSMETIC INDUSTRY 345 make-up preparations, flocculation must be avoided. Otherwise a coarse, unattractive precipitation will occur quickly. The consistency of a paste depends largely on degree of fiocculation. Often a very firm paste will break down at once to a liquid or semiliquid when a trace of defiocculating agent . is added. These considerations become very important whenever it is desired to obtain a paste of standardized thickness. CONCLUSIONS The foregoing discussion has neces- sarily been incomplete. Important fields of surface chemistry and cos- metic practice have been omitted or mentioned briefly in passing. To those who are not familiar with the science of surface chemistry, the treatment has probably been sug- gestive rather than informative. Today, with so many new ma- terials and new techniques available, workers in the field of cosmetic science require at least a working knowledge of the principles of sur- face chemistry. Without that, one is reduced to wasteful trial and er- ror or dependence on manufac- turers' recommended formulas. Par- ticularly is this true for the use of the surface-active agents. In the versa- tility of the newer non-ionic agents, in the bactericidal action and unusual wetting properties of the cationic agents, in the incompletely explored special properties and synergistic effects of all classes of these agents, lie the unborn cosmetics of the fu- ture.

SURFACE-ACTIVE AGENTS IN COSMETICS* By H^RR¾ C. SPEEL tintara ]roducts, New York, N.Y. THE TASK OF CHOOSING the proper surface-active agent to use in formulating specific cosmetic prod- ucts is often a complex problem. Evidence of this is found in the numerous lists and attempts to classify the hundreds of such agents that are offered to formulatots in virtually every field of industrial activity (2, 4, 17, 23, 28). Actually, the total consumption of surface- active agents by cosmetic manufac- turers is relatively small, probably less than 5 per cent of the available production. But the existence of thousands of cosmetic manufac- turers with their millions of custo- mers makes the cosmetic field a po- tential customer for almost every new product the chemical manufac- turer can make. If the new agent is not quite suitable, he will try to "tailor-make" one more suitable, thus further increasing the available number. The term "surface-active agent" is, of course, a broad one applied to organic chemicals used for wetting, penetrating, emulsifying, dispersing, solubilizing, foaming, and deter- gency. Personally, I like the defi- nition of a surface-active agent being a product which brings unlike * Presented at the December 3, 1947, Meeting, New York City. surfaces together closer, faster. It imparts a sort of "sex appeal." a quality widely advertized for cer- tain soaps. Indeed, soap is the oldest and best known of all surface- active agents made by man. These agents are all characterized by their ability to modify the surface prop- erties of the medium to which they are added. For example, most agents will make water wetter, though certain types are superior as penetrating wetters and others excel as spreaders. One kind of agent will cause a liquid to foam another will kill foam. Emulsifying types help make oil and water mix and stay mixed. Dispersion of solids in a liquid is aided by certain agents other agents reverse the process. No one product excels in all applica- tions. The problem is to classify these agents and to match their peculiar properties with the needs of formulation of specific products. The primary functions of a sur- face-active agent are the result of proper blending, or balancing, of the raw materials from which it is made. Synthetic surface-active agents, like common soap and agents that occur in nature, are the result of a com- bination in one molecule of a water- seeking or hydrophilic portion, and an oil-seeking lipophilic, or hydro- 346