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

SWELLING OF HAIR IN THIOGL¾COLATE SOLUTIONS 97 waving lotion. Probably in the center of tightly wound curls which are repeatedly saturated with the waving lotion a condition approaching com- plete immersion exists. However, the outside of the curls are exposed to the air so that the normal waving time for most home permanents of one hour or more (including the winding time) is probably less severe than thirty minutes immersion in the waving lotion. DenBeste (5) suggests that the reduction of the keratin occurring on complete immersion in a huge excess of ammonium thioglycolate is four times the reduction ob- tained during an average permanent wave. 330 J i i i 300 120 270 • 240 60 • 1•0 150 • 120 9O 6O 0 1 2 3 4 5 6 PERCENT THIOGLYCOLIC ACID Fig, 5: -Effect of increasing concentration of ammonium thioglycolate on the swelling of hair. EFFECT OF INCREASING THIOGLYCOLATE CONCENTRATION Figures $ and 6 show the effect of increasing concentrations of ammonium thioglycolate on the degree of swelling. It is interesting to note that con- centrations above 3 per cent give a sharp increase in swelling. This is surprising since these higher concentrations are not needed to give complete reduction of disulfide groups in the human hair. Since the ratio of hair to solution is 1: 100 there should be sufficient reducing agent in even the 1 per cent solution. It is probable that the higher concentrations of the thioglycolates give greater swelling due to effects other than the reducing action and pH. In one hour of swelling a 4 per cent ammonium thioglyco- late solution gives three times the swelling given by a 2 per cent solution in spite of the fact that both solutions contain enough reducing action to completely reduce any disulfide groups that may be in the hair keratin.