HAIR AND WOOL 779 7. Supercontraction and Set Different animal fibers exhibit a wide range of supercontraction values after an hour's boiling in several media (35). The kinetics of the process for different fibers have been examined in 9 M LiC1 (24) and in cuprammonium hydroxide (36) with similar results: hair has a much longer initiation period before the onset of supercontraction and a slower rate of supercontraction (or generation of tension) the level of con- traction or maximum force attained is sometimes also lower. Typical data are shown in Fig. 6. In examining the acceptance of set by stretched keratin fibers in boiling water or borax, Mitchell and Feughelman (37) found that the amount of set diminished as the fiber diameter increased. On the other SETTING IN BOLLING pH 7 BGFFER I • WOOL / • 0 / L•" , , , , , -10 -20 I II•k/* I I i 0 60 120 180 240 300 380 SETTING TIME, MINUTES Figure 7. Rate o[ set generation as a [unction o[ time of setting, at 40% extension (one hour's re- lease in the same medium) hand, Whewell (38) reports some specific differences: in setting fibers in boiling water for 2 hours, he obtained 12•o set in hair and values ranging from 6 to 21• for four samples of wool. Data from these laboratories show that Lincoln wool accepts set more rapidly than hair. The curves of Fig. 7 illustrate the results obtained with fibers set at AO• extension in boiling pH 7 phosphate buffer for the time indicated and released for one hour in the same medium. The amount of set is affected by holding the fiber under strain prior to exposure to the setting process this fact was noted at an early stage of studies in this field (27). The authors find that the extent of super-

78O JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS -5 -10 -15 -2O Figure 8. MINS SETTING, 30 MtNS RELAXATION IN BOILING WATER, 40% EXTENSION • •'ø• o . J HAIR , • • L , ' •' 1'6 1 2 3 4 5 6 TIME IN COLD WATER PRIOR TO SETTING, HOURS Set as a function of time extended, in cold water, prior to setting contraction obtained after 2 minutes' setting at 40% extension, followed by 30 minutes' relaxation (both in boiling water), diminishes linearly with the time the fiber is held stretched prior to setting (Fig. 8) here again, hair has less supercontraction at any given time than Lincoln wool, but the decrease in supercontraction with time under tension runs in parallel for the two fiber types. III. CAUCASIAN AND NEGRO HAIR A. Materials 1. Caucasian ttair--Brown European hair, from mixed women's combings, purchased from a New York hair dealer, was employed. The hair was about 28 cm long, in the "remis" state (bundled, root-to-tip oriented). In one experiment (Table IV), white hair from the same source was used. 2. iVegro Hair--A blended batch of barber's clippings from a Chicago barber shop, 3-6 mm long, from some thirty male heads* was the material used in all the work other than the tensile tests (Table VIII) these were carried out on fibers from one female head, purported to have had no hot combing or chemical treatment. 3. Lincoln Wool--This was a sample (SW 296) of one of the "Stand- ard Wools" derived from pen-reared sheep maintained in the CSIRO * Kindly provided by J. L. Underwood, The Toni Co., Chicago, Ill.