SWELLING OF HAIR IN THIOGLYCOLATE SOLUTIONS 95 ua 60 n. 55 (_3 • 50 OH ,1- • 45 •: 4o bJ • •-•OH bJ •- 35 HC],•,,•,,,,.,,,,• 30 WATER 28%- NH40H i i i I i i i 0 2 4 6 8 10 12 14 pH Fig. 1.--Effect of pH on swelling of hair using HC1, NaOH, and NH4OH swelling measured after 3 days immersion. and decomposition occurs. It is surprising, however, how resistant the hair is to the attack of strong ammonium hydroxide solution at room tem- perature. EFFECT OF PH IN SWELLING IN THIOGLYCOL1C ACID Figure 2 shows the swelling of hair in acid solution when the pH is raised from 2.0 to 10.0 using thioglycolic acid and the required amount of am- 300 260 220 180 140 100 6O 2O I I I mln I I i i I i I i i 1 2 3 4 5 6 7 8 •o 0 pH Fig. 2.--Effect of pH on swelling of hair in 6% thioglycolic acid and ammonia.

96 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS monia. The hair was immersed from periods of 15 minutes up to an hour with little additional swelling occurring after the first 15 minutes. It is interesting to note that there is an area of increased swelling at a pH of 2.0. It is also surprising how sharply the swelling increases at 9.0. Going from a pH of 8.8 to 9.4 more than triples the amount of swelling and there is no evidence that the reducing value of the salt rises sharply at 8.8 or that the hydrolyric degradation with ammonia increases strongly at this point. In any event this system becomes a much more effective swelling medium above 9.0. 360 i i i i i i • i pH 9,6 - pH 9.2 pH 8.8 • pH 8.0 o o 15 $o 45 60 90 12o MINUTES Fig, &--Swelling of hair in 6% ammonium thioglycolate. $oo "' 260 z 22O • 140 •J i i i i• 0 $0 6 0 120 150 180 210 240 MINUTES Fig. 4.--Rate of swelling of hair in 6% ammonium thioglycolate pH 9.2. RATE OF SWELLING Figures 3 and 4 show the rate of swelling of hair immersed in solutions of 6 per cent ammonium thioglycolate and ammonia at pH's of 8.0, 8.6, 9.2, and 9.6. Within the first half hour the major portion of the swelling occurs. Longer periods of swelling show some evidence of degradation. It should be remembered that in the cold waving of hair it is briefly immersed in the