SHAMPOO FORMULATION 359 Surface-active agents differ in the ease with which they lather on the skin or hair often several lather- ings are required. While defoaming . by the fatty acids present on the hair and skin is undoubtedly re- sponsible for some of this poor lathering, adsorption of the surface- ß •: : ': active agent on the skin would, of course, render this material unavail- able for lathering. (4:) Salts of sur- face-active anions and slow rinsing organic bases might be useful in decreasing or eliminating the scroop" effect. (5) If it is desir- able to duplicate the effects pro- duced on the skin and hair by soap, synthetic surface-active agents with carboxyli'c • acid groupings, but with better hard water properties, could be utilized. Materials of this sort have been: described and have actu- ally been found to be excellent skin detergents. Experiments devised to determine the role of conditioning agents, un- fortun&rely} have not been very successful. These materials--added to shampoo detergents to improve softness--are generally non-ionic agents, a typical example being lan- olin. Addition of this and other ma- terials to alkyl aryl sulfonates did not appreciably affect the feel pro- duced. There is evidence (11), however, that lecithin (a phospholip- oid) and fatty esters of diglyce•øl do modify the adsorption properties of anionic' and cationic agents on cell membranes as they inhibit germicidal activity. Incidentally• it is possible' to demonstrate visually the adsorpi•'i'on of quaternary atom0- nium compounds on glass surfaces (12) by development of rainbow color effects when steam is con- densed on the surface the addition of a wide variety of non-ionic agents did not appreciably affect the de- velopment of rainbow co)or, al- though the effect of pH was con- firmed as in the case of protein ad- sorption. The apparent contradiction in- volved in producing "scroop" on the skin by adsorption of surface- active agents of the type used as lathering agents, and the producing of softness by other surface-active agents, may be resolved as follows: These latter materials are all straight chain compounds. The theory of lubrication as developed years ago indicates that such ma- terials are much better lubricants than the shorter chain compounds of the type used for shampooing. Hydrophilic groups also affect lubri- cating properties. Aromatic char- acter is also known 'to affect lubrica- tion adversely. This all• corre- sponds with the observation that alkyl aryl sulfonates and. alkyl naphthalene sulfonates produce much harsher feel than straight chain alkyl sulfonates.. It was thought that perhaps the feel and frictional properties of the skin might be due to the presence of hy- drophilic groupings on the outer side of the surface-active agent film. There is some evidence that this type of arrangement does occur in some cases. However, it has been found that regardless of the type of film which may be on the skin'sur-

360 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS ß face, water droplets do not tend to spread readily and the surface of the skin cannot be considered as particularly hydrophilic even when •clean? • There is little question that the work being done on combination of surface-active ions with proteins is of considerable importance and sig- nificance to the cosmetic industry. Contributions in this field are ap- pearing at an accelerated rate and while often difficult to follow because of highly mathematical treatments, well deserve the attention of the cosmetic chemist. Another common misconception is that soap is not suitable for formu- lation of hard water shaml:(OOS. There is no question that soap--es- pecially coconut oil soap•has many desirable properties not easily dup- licated by synthetics. Aside from the fact that s. oap produces the con- ventional feel of skin and hair, the lather produced by coconut soaps is excellent. It is copious, viscous, and stable in soft water. It rinses readily in soft water. In hard wa- ter, the volume and viscosity of the lather fall and during the rinsing operation, the dilution of soap with large quantities of water containing calcium and magnesium results in the precipitation of the correspond- ing alkali earth soaps on the hair. The inclusion of water-softening agents in liquid soaps is now widely practiced due to the improved availability of organic sequestering agents which are compatible with potassium and triethanolamine soaps and which do not hy•irolyze on storage in aqueous solutions. Typical of such products is ethyl- enediamine tetraacetic acid. The neutral and alkaline salts form chelate complexes with 'cal- cium and magnesium (13) and thus prevent the precipitation of soap by these ions. It is now possible to manufacture liquid soaps which often do not require refrigeration or filtering and which will not cloud in glass containers. The addition of a few per cent of ethylenediamine tet- raacetate to a soap shampoo will prevent the decrease in lather vol- ume and viscosity in hard water. Foam measurements on dilute solu- tions of soap and sequestrant have been made (13) and these results have also been confirmed for high concentrations of soap. Five per cent solutions of soap containing 0.5 per cent ethylenediamine tetra- acetate show no drop in lather vol- ume or viscosity at 500 ppm. hard- ness as tested in a Waring blendor. This concentration of sequestering agent is also adequate to neutralize such hardness as may be encoun- tered on preliminary dilution and rinsing of the lather. It is not adequate, however, to neutralize the hardness of all the rinse water used, and in all probability these organic sequestrants rinse faster than does the soap, leaving it un- protected. The precipitation of calcium and magnesium soap on the hair during dilution may be prevented by the addition to the soap of a lime-soap dispersant. The function of this material is perhaps more correctly