CUTTING OF BEARD HAIR o- o Before x - x After 587 12 11 10 ø x x x o x o x o o 0 1 2 3 4 5 10 Time (Minutes! Figure 6. Hydration time before and after washing with sodium ]aury] sulfate (0.5 per cent) at 23 ø C value * (2) a stream of water or of a test solution was directed at the fiber, and cutting forces were determined as rapidly as possible during the first 9. rain after this, cuts were made at 1 min intervals (3) after 10 mina series of 10 cuts were made as a measure of the equilibrium cutting force in the wet state. *Fig. 5 shows that the "dry" f-t-c is relatively insensitive to variations in the range of 10 to 60 per cent relative humidity.

588 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table II Hydration Time and Cutting Force as a Function of pH pH 9.1 6.84 4.01 Buffer 0.01 M borax 0.05 M phosphate 0.05 M phthalate Hydration time (rain) ñ std dev. 2.60 ___ 0.47 2.13 ñ 0.26 2.16 ñ_ 1.21 Force to cut wet (g) 4- std dev. 4.01 ñ 0.40 3.91 ñ 0.39 4.31 4- 0.31 Ionic Strength of buffer 0.060 0.091 0.053 The results of a typical experiment are shown in Fig. 6. Fo.llowing the determination of the initial hydration curve at 23øC (Fig. 6, before), the fiber was washed in 0.5 per cent aqueous sodium lauryl sulfate solution, rinsed with distilled water, and dried for 48 h in a desiccator over P205 a sccond hvdration curve was then detcrmincd (Fig. 6, aftcr). The absence of any significant difference suggests that the rate of hydration is not altered bv the removal of surface lipids. Based on the f-t-c, beard hair fibers appear to have been completely hydrated by exposure to water at room temperature within about 2 to 3 min. The rate of hydrarich of beard hair and the f-t-c could be expected to be dependent on the pH of the aqueous medium. Accordingly, cutting measure- ments were made in various buffer solutions, and the results are summarized in Table II. Any differences between the hydration times or between the f-t-c are sta- tistically insignificant. The ionic strengths and chemical composition of the buffers are different, but the variations are not likely to affect the results. These rather unexpected data indicate that the pH has little or no effect on the f-t-c or on the rate of hydration of beard hair. Effect of Temperature on Cutting Force It is part of shaving folklore that the use of cold water during shaving leads to an uncomfortable shave. It seemed important, therefore, to measure the effect of water temperature on the cutting force. Three types of experi- ments were performed on wet fibers and on dry fibers. For measurements on dry fibers, the fixture used for cutting beard fibers was fitted with a heating tape and a surface thermocouple. A single hair was cut (dry) 10 times at each of 4 temperatures. The average cutting forces and the standard deviations are tabulated in the chart below and indicate that the f-t-c of dry fibers is lowered by raising the temperature. Temperature (o C) 23 56 65 75 f-t-c (g) ñ std dev. 17.6 ñ 1.5 14.5 4- 1.3 12.3 ñ 0.80 13.1 ñ 0.84 Significance (Values connected by underlining are significantly different) _