356 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS face lipoids, it may be desirable to describe the so-called defatting re- action of synthetics in sensory terms. If the hands are washed with a rela- tively concentrated solution of puri- fied neutral Cn alkyl aryl sulfonate, a copious lather with good lubricat- ing properties may be worked up. As the hands are rinsed and as the suds disappear, one becomes aware of the abrupt development of a high coefficient of friction making it very difficult to pass one palm over the other a peculiar crackle is also pro- duced. On towelling the hands a tackiness may be noted but this dis- appears on complete drying. If the hands are rewetted, the high coef- ficient of friction of the skin is again evident. This sensation is generally believed typical of ultra- clean skin. Now if this is true de- fatting there are several facts which are rather-difFicult to explain: (1) Short chain alkyl naphthalene sulfo- nates which are notoriously poor detergents and fat emulsifiers pro- duce the same effects as the high molecular weight alkyl aryl sulfo- nates while oleic acid soaps, which are generally conceded to be excel- lent fat emulsifiers, do not "di'y" the skin. (2) Real defatting of the skin with organic solvents does not produce effects similar to those ob- tained even with the most powerful neutral synthetic detergents. (3) The skin of the palms, where the "drying" effect of the synthetics is most pronounced, is notably lack- ing in sebaceous- or oil-secreting glands. These circumstances sug- gest that actual defatting of the skin may not be a satisfactory ex- planation for the phenomenon just described. , The effects produced on the skin by synthetics may be better de- scribed as "scroop" to borrow a term from the textile industry--this is a finish imparted to silk by treat- ing with dilute organic acid. It is characterized also by a h. igh coefFi- cient of friction and a crackle or rustling sound when the silk is rubbed on itself. Going back to the demonstration of "scroop" produced on the skin by the alkyl aryl sulfonates, it will be remembered that after rinsing and drying the skin was considered clean. If the hands are now rinsed with dilute sodium carbonate (less than 0.25%), it is possible to work up a suds again at the same time the normal feel of the skin is re- stored and now remains unchanged even after copious rinsing with pure water. The skin, of course, is pre- sumably no cleaner now than be- fore. This suggests that the sensa- tion of an ultra-clean skin surface was produced actually by an ad- sorbed film of surface-active agent. In[identally, if the hands are washed with alkyl aryl sulfonate at neutral pH in the presence of sodium sulfate, or at pH 3 to • in the pres- ence of organic acid, the "scroop" effect produced is considerably en- hanced in either case, rinsing with dilute alkali restores the normal feel. C-12 alcohol sulfates and alkyl sulfonates of low salt content at neutral pH produce less "scroop" than do the alkyl aryl sulfonates..

SHAMPOO FORMULATION 357 ??: At acid pH's, however, the "scroop" is more pronounced although not as fully developed as in the case of al- kyl aryl sulfonates under comparable conditions. The quaternary ammonium com- pounds produce somewhat different effects. On washing the hands with Altosept MB (alkyl imidazolinium chloride) or cetyl trimethyl ammo- nium bromide at pH 7, one becomes acutely aware of the ridges in the palms and fingers at alkaline pH's mild "scroop" is developed. In either case, after rinsing the hands hoogn, dilute acid will produce a very copi- ous suds and the "scroop" will al- most disappearsalmost, because a rinse of normal skin with dilute acid alone will cause a slight increase in friction. With non-ionic surface- active agents "scroop" effects are not marked although adsorption seems to occur to a limited extent as evidenced by slight sudsing after rinsing with water followed by a pH shift to the alkaline side. In short, the so-called drying or defatting effects of the synthetics may be explained in terms of adsorp- tion phenomenon. Fortunately, the adsorption of surface-active ions by proteins has attracted the consider- able attention of textile technolo- gists and biochemists. Work in this field has recently been reviewed by Putnam (2), Valko (3), and Harris (4). Complex formation between surhce-active ions and proteins is generally explained in terms of what is called "specific or intrinsic a•n- ity" and electrostatic forces. At its isoelectric point a protein is consid- ered electrically neutral. At pH's below its isoelectric point, the pro- tein becomes positively charged and cationic in nature under these conditions it combines with nega- tively charged colloids in which class are the anionic surface-active agents. At pH's above its isoelectric point the protein becomes nega- tively charged and anionic in char- acter under these conditions the protein will combine with positively charged colloids in which class are the cationic surface-active agents. The extent of protein surface-active ion complex formation is determined by hydrogen ion concentration and by electrolyte concentration. Ac- tually, however, solid proteins do adsorb anions at alkaline pH's and cations at acid pH's this is "ex- plained" in terms of intrinsic af- finity of the surface-active ion for the protein. Neville and Jeanson (5) in 1933 described the adsorption of lauryl sulfate and also Igepon T by wool at pH 1 the wool adsorbed 25 to 40 per cent of its weight of surface-ac- tive anion from a 0.5 per cent solu- tion. As the pH increased the ad- sorption decreased, although even above the isoelectric point of the wool adsorption is 2 to 3 per cent. Steinhardt, Fugitt, and Harris (6) investigated the adsorption of vari- ous anions by wool over the pH range of 1 to 6. While maximum adsorption of dodecyl sulfonic acid was approximately 25 per cent at pH 2, at pH 6 100 gm. of wool would still adsorb 1.2 gin. of anion. It was