JOURNa, L OF THE SOCIETY OF COSMETIC CHEMISTS ,511 ::4 ,. ,: ß Figure 1. Electron micrograph of untreated cellulose acetate staple fibcr. tainly reveals some surprising facts, as the accompanying electron micrographs of cellulose acetate staple fiber show (5). The untreated fibers (Fig. 1) are smooth, but their feel is most unpleasant, whereas the treated fibers (Fig. 2) have a soft, vicuna-like feel in spite (perhaps, because) of the fact that the surface deposit of silicone is irregular. By means of the Stereoscan the extent to which feel is influenced by the nature and distribution of the deposit can be readily elucidated and the art transformed into an applied science. HYDROPHOBIC SIDE-CHAINS Proteins like zein, which are rich in hydrophobic side chains, are remarkable in being soluble in aqueous propanol. Although the com- plete amino-acid analyses of wool, which were obtained in 1955 (1), revealed the presence of a high proportion of acids with hydrophobic side chains, as shown in Table III, little use has been made of the infor- mation.

512 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Ftgure 2. .• . . • •:' .':•,• ?(• • .*,7 :-:.'.::.:x. :•- ,•. •.'.•.-- ... Electron mirograph of cellulose aee•te staple fiber treated with a surface deposit of silicone It was only in 1959 (6) that wool fibers were found to be more resistant to extension in water than in n-butanol saturated with water, and further study of the action of aqueous alcohols on wool and hair has since shown that the maximum weakening is given by an aqueous solution of n-propanol (45% w/w) (7). The weakening, which is associated with enhanced swelling, is clearly analogous to the dissolu- tion of zein by aqueous propanol, and is presumably due to the action of the alcohol molecules in associating with the hydrophobic side chains of the fiber and reducing the cohesion between them. This unexpected behavior of aqueous alcohols has some bearing on solvent- assisted methods of dyeing keratin at low temperatures, and further work has revealed other new media for increasing the swelling and accessibility of wool and hair to different reagents (7). The available media cover a wide range of conditions: aqueous propanol (45% w/w) and aqueous formamide (89% w/w) are neutral, aqueous pyridine (54% w/w) is weakly alkaline (pH 8.3), and aqueous trichloroacetic acid, or, better, a solution of the acid in aqueous propanol (50% w/w) is acidic.