SWELLING STUDIES OF SINGLE HUMAN HAIR FIBERS 247 Figure 3. and a drop of Vinylite solution is used to anchor the fiber to the sec- ond Vinylire spot. The excess hair is clipped off and the mount placed in the 105øC. oven fi•r two hours to evaporate the acetone. Also the hair is dried to a constant moisture content so that the initial diameter is constant. The mount is held in place by means of the two phosphor bronze clips on the cell. Stopcock grease is used to keep the cell from leaking. The apparatus which has been described is used with a Bausch and Lomb binocular microscope. With the 8-min. objective, a total mag- nification of 430 diameters is ob- tained. We found that we could not use the 4-min. objective, since the fiber was then out of focusing range. The general procedure for the use of this apparatus is as follows: The hair fiber mount is placed in position on the cell, sealed with stopcock grease, and held with the spring clips. The cell is put in place on the mechanical stage and connected to the manifold. The microscope is focused on the hair fiber close to the anchored end and the original dry diameter noted. The first reagent to be used is then admitted to the cell and a stop- watch started simultaneously. have found that readings can be comfortably taken and recorded at one-half minute intervals. After the desired reaction time or degree of swelling the reagent can be changed, and readings continued. Although there are several ways of arranging the data, I have found it convenient to calcula_te the per- centage of swelling over the dry diameter as a basis for reporting and correlation. The first experiment to be dis- cussed was not really planned in its entirety. In an earlier experiment we tried to find a relation between stress-strain data and certain swell- ing phenomena. Although this ex- periment did not lead to any c,•n- elusive relation, examination of the data indicated that the amount of deswe!ling by potassium bromate of a fiber which has been swelled by treatment with ammonium thio- glycolate was exactly dependent upon the extent of the thio-induced swelling. In order to confirm this idea, several more fibers were treated for various periods of time with ammonium thioglycolate followed

248 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS by deswelling with potassium bro- mate. Over a broad range of thio swelling, there is a linear correla- tion between the extent of swelling in ammonium thio and the deswell- ing by potassium bromate. The data oerom this experiment are shown on Fig. 4. 6O •o •o AMM.THIO. IO O 0 5 I0 15 20 25 30 % Swelhn• in KBrO• Figure 4. The significance of this relation- ship in cold permanent waving is quite obvious. The less swelling a fiber undergoes during the process- ing period, the more complete will be its return to normal diameter during the neutralizing step. Since one of the most desirable character- istics of a permanent wave is to leave the hair as close to its original state as possible, a means of chang- ing the linear relation shown here to a hyperbolic relation should be sought ideally, regardless of the extent of swelling upon treatment with the waving solution, the hair should be deswelled as close to the original as possible. An interesting and useful rela- tion was revealed when the degree of swelling in ammonium hydroxide was compared to cystine values for reduced hair wh.ich was oxidized to various degrees by potassium bro- mate. Fibers were swelled to about 50 per cent over the dry diameter with ammonium thioglycolate. Then the thio was replaced with a solution of potassium bromate. After varying intervals the bromate solution was replaced with a 6 per cent solution of ammonium hydrox- ide. In a parallel experiment, hair treated in the same fashion, except for the ammonium hydroxide, was analyzed for cystine content by the Sulhvan method. Application of ammonium hy- droxide to the partially oxidized hair reswelled the hair to various extents. This difference between the bromate level and ammonium hydroxide level against the per cent cystine has been plotted in Figure 5 % Cystine 0 •0 20 30 40 50 60 70 60 90 DiFference between NH•OH and K3rO, levels Figure 5. The inverse linear relation ob- tained here has not been satisfactor- ily explained however, the ammo- n ium hydroxide reswelling has proved to be useful in evaluation studies of permanent wave oxidizing agents. The next experiment to be dis- cussed was a result of an observa- tion made during earlier work when