MOLECULAR FORCES IN PERMANENT WAVING 337 decrease in curl strength is readily observed while the addition of 1 M salt tends to lower the level of hair reduction slightly, the effect of sulf- hydryl generation is s•nall co•npared with the effect on the strength of the wave. With saturated MgSO4, the ability of the thioglycolate to reduce the hair has definitely decreased, but the curl i•nparted is virtually nil. Similar results are obtained with other salts such as sodium sulfate. SECONDAI•¾ BONDS AND CURL STABILIZATION Thus far, the experimental results have been concerned with secondary forces in the wave generation step in which lotion acts on the fiber. If it is argued that during generation of the wave, covalent and secondary bonds must be broken, then stabilization of the wave in the newly formed con- figuration should occur by rebuilding some of these same types of molecular bonds. Conventionally waved hair is stabilized by rebuilding of cross links through treatment of the reduced hair with oxidants such as sodium bromate or perborate, or hydrogen peroxide, and this reaction is usually described as the re-oxidation of sulfhydryl groups in the hair to reform disulfides (16, 11b), although new secondary bonds must also form. To isolate the contribution of secondary bond rebuilding, it was of interest to determine whether stabilization of curl could be produced experimen- tally without reformation of the keratin disulfide bonds. Since atmospheric oxygen is known to oxidize thioglycolate ion (11a) and sulfhydryl groups in hair (17), experiments were performed under anaerobic conditions in the apparatus diagrammatically shown in Fig. 4. The apparatus permitted reinoval of air by alternate cycles of evacuation Figure 4. Apparatus used for waving in oxygen free atmosphere. (A) waving chamber (B) hair tress on rod (C) transfer flask (D) reserve pressure chamber (E) to manometer (F) to helium (G) to vacuum pump.

338 JOURNAl. OF THE SOCIETY OF COSMETIC CHEMISTS Figure 5. Waving in an inert atmosphere. Hair tresses were waved by treating with thioglycolate lotion for 15 min., water rinsed and allowed to process for the times shown. In the case of the tress on the right only, peroxide neutralizer was applied after the rinse. In all cases, all operations were conducted in substantially an oxygen free atmosphere using the appa- ratus shown in Fig. 4. The tresses were shampooed immediately on removal from the apparatus after sampling the hair for sulfhydryl analysis. and filling with inert gas helium was selected since it was available sub- stantially free of oxygen. The hair was wrapped on the hollow waving rod initially all air was removed and replaced with helium by successive flushing of the apparatus, and all subsequent operations such as lotion application and rinsing were conducted using the pressure of the inert gas. In Fig. 5 some waves produced in the inert atmosphere with a conventional type of waving lotion are shown the process involved fifteen minutes of processing time, a rinse with de-aerated water and a waiting period of the duration shown. For comparison the tress on the right was chemically neutralized with peroxide after fifteen minutes while none of the others were oxidized. Immediately on removal from the apparatus, samples were taken from the hair tresses for analysis of the sulfhydryl content and the waved hair was shampooed. The photograph illustrates that an ap- preciable amount of curl is produced under the test conditions and that the waves so produced are indeed stable to shampooing. This permanence exists despite the high level of reduced disulfide in the form of sulfhydryl shown in the analytical data in Fig. 5. The permanence of curl to sham- pooing cannot then be explained by the rebuilding of disulfide in the waved configuration, and it must be concluded that stabilization is brought about by secondary bonded cross links. RELAXATION OF WAVED HAIR If the permanent waves produced by treatment in an inert atmosphere are indeed stabilized by secondary forces, it should be possible to destabi-