HAIR AND WOOL 777 slopes of the lines are in the ratio of 3.9:1 correcting for the difference in mean fiber diameter between the two substances, the rates of diffusion are in the ratio of 2.2:1. (The staining of cross-sections with hydrogen sulfide showed that reagent diffusion was indeed the rate-controlling factor.) The "half-reaction times" are 5 hours for the wool and 75 hours for the hair--a fifteen-fold difference. 6. Rates of Reaction Differences in reaction rates among the keratin fibers are well demonstrated in the two standard solubility tests, in urea-bisulfite (30) • 20 gig lad ,-- 10 F4gure 6. SUPERCONTRACTION FORCE IN 9M LiCI AT 97øC [Rebenfeld, Weigmann, Dansizer, 1963] RINO WOOL / HAIR / / / / / / 10 20 30 40 50 TIME. MINUTES Rate of development of supercontraction stress (24) and in alkali (31). The urea-bisulfite test distinguishes quite sharply between wool and hair, the former being soluble to the extent of about 50%, the latter about 15% (32). In the alkali-solubility test, intact keratin fibers all exhibit fairly small weight losses (4-6r•o for hair, 10-12% for wool). The weight loss is increased by prior exposure to oxidizing agents or acids this increase is much greater for wool (and mohair) than for human hair (10). The effect of exposure to boiling 0.04 N sulfuric acid is indicated in Fig. 5, where alkali insolubility (the weight fraction remaining after the test) is plotted, on a logarithmic scale, against the time of treatment with acid. The differences in ease of degradation are evident in microscopic examination: wool fibers, pretreated with acid and then examined in alkali, swell and lose their birefringence very rapidly, whereas hair is quite resistant (13). They are also reflected in the mechanical proper- ties of the fiber, as indicated by the data of Table III (33).

778 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table Fractionation Keratose (%) Fiber Type a • T Total* Merino wool (34) 56 10 25 91 Caucasian hair 43 15 33 91 Negro hair 43 14 33 90 Sulfur Content (%) a • -/ Whole Fiber Merino wool (34) 1.88 2.13 5.84 3.38 (2.72) Caucasian hair 2.56 3.69 6.04 5.45 (3.65) Negro hair 2.38 4.00 6.60 5.40 (3.77) * The totals do not sum to 100%, due to incomplete recovery the deficit is believed to reside mainly in the -/-fraction. } The figure in parentheses represents the sum of the sulfur contents of the three fractions. Table VII Moisture Regain at 22øC Desorption Regain at Absorption Regain at Fiber Type 65% R.H. 87% R.H. Lincoln wool 15.4 23.4 Merino wool 14.8 . . . Caucasian hair White 15.2 23.3 Brown 16.2 24.1 Negro hair 16.0 24.4 Table VIII Tensile Properties Yield Stress Breaking Stress Extension to Fiber Type Denier (g/denier) (g/denier) Break (%) 65% R.H. Lincoln wool 20 1.10 Caucasian hair 46 0.93 Negro hair 37 1.11 pH 7 Buffer Lincoln wool 20 0.35 Caucasian hair 42 0.42 Negro hair 38 0.46 2.04 1.68 1 81 1.70 1.41 1.24 43 44 4O 65 47 48