MERCAPTANS IN COSMETICS 29 will remove hair without irritating the skin. To illustrate this Table I has been prepared. TABLE I--EFFECT OF PH oN RATE OF DEPILATION BY MERCAPTAN pH Hair Removal in Time to Irritate 8.0 Not in 30 min. None in 30 min. 8.5 Not in 30 min. None in 30 min. 9 0 30 min. None in 30 min. 9.5 24 min. None in 30 min. 10.0 19 min. None in 30 min. 10.5 15 min. None in 30 min. 11.0 12 min. None in 30 min. 11.5 9 min. None in 30 min. 12.0 7 min. None in 30 min. 12.5 5 min. Slight in 30 min. 13.0 3 min. Severe in 15 min. Thioglycolic acid (0.5 molar) was used in this experiment because we had found that substituted mer- captans were not only better because of their odor but also more effective . and less irritating. Of the sub- stituted groups we had found the ionizing groups, particularly the acidic groups such as --COOH, to be preferred over the non-ionizing groups such as the ether groups. 2. The concentration of the mer- captan should be greater than 0.1 mole per liter of solution and need not be greater than 1.5 moles per liter. To illustrate this 'Fable II has been prepared. 3. Any non-volatile alkaline ma- terial can be used provided that a) its dissociation constant is greater than 2 X 10 -s and b) it does not form an insoluble salt with the particular mercaptan. For ex- ample, monoethanolamine alone even when used in sufficient amount to give a pH of 11 will not make a satisfactory depilatory and barium hydroxide is not usable with thio- glycolic acid because it forms an in- soluble salt. 4. Although it is preferable to have the concentration of the alka- line material slightly greater than the total acidic equivalency of the mercaptan, it should never be greater than twice. 5. The filler or cream-forming materials serve an important func- tion in mercaptan depilatories other than just the ease of localizing the depilatory in application. As mer- captans in an alkaline medium oxi- TABLe II--EFF•CT OF CONCENTRATION OF MERCAPTAN (THIoO, LYCOLIC ACID) ON RATE OF DEPILATION Molar Concentration pH by Excess Irritation of Thioglycolic Acid Ca(OH)2 Time to Remove in 30 Min. 0.05 12.35 None in 30 min. None 0.10 12.30 Partial in 20 min. None Complete in 30 min. 0.20 12 28 Partial in 10 min. None Complete in 15 min. 0.50 12.29 Partial in 6 min. None Complete in 9 min. 0.80 12.26 Partial in 6 min. None Complete in 9 min. 1.50 12.26 Partial in 8 min. None Complete in 10 min. 2.00 12.28 Partial in 8 min. None Complete in 10 min.

30 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS dize rapidly, the thicker application serves as a protection from oxidation by the air while the mercaptan is acting at the level of the skin. Also, because the free liquid content of the cream is low, the danger of irritating the follicle is obviated. The choice of fillers or cream-forming materials is much wider with mercaptans than with sulfide depilatories. 6. Because the substituted mer- captans produce depilatories that are substantially non-odorous, one is likely to overlook that they have solved one of the most troublesome problems associated with sulfide depilatories, namely, that of perfum- ing the product. As stated by Koeune, this is not merely a matter of covering the odor of the depila- tory but of finding aromatic ma- terials which will not be destroyed or changed into foul-smelling com- pounds by the ingredients of the depilatory. With the mercaptan depilatories we have found that a much wider choice of perfume ma- terials is possible not only because lighter fragrant types may be used but also because many perfume ma- terials destroyed or changed by sulfide depilatories remain un- changed in mercaptan depilatories. 7. The mercaptan depilatories are less irritating than the sulfide depilatories. On this point our original findings have been con- firmed by 6thers. For example, Consumers Union reported(8) that thioglycolate depilatories "are some- what milder in their action than the sulfide depilatories and medical authorities believe that they are less likely to cause dermatitis than the sulfides." During an epidemic of ringworm in Hagerstown, Maryland, when a commercial thioglycolate depilatory was applied to even the infected areas on a large group of school children for the removal of hair, there were no unfavorable results. The thioglycolate depilatories were first offered to the American public in June, 1939, and although the war has hampered their exploi- tation, nevertheless, it is estimated that this year the sales of cosmetic depilatories will be approximately three times the sales of any previous year, and more than ten times the amount sold in •938. The mercap- tan depilatories will be the reason for that advance. MERCAPTANS IN COLD WAVING The depilatory market, though, cannot even approach that of cold waving, because the income from this source is derived not only from sales of the product for use at home but also from the huge amounts of the product used in the beauty shop. Within the short period of five years cold permanent waving has become the preferred method of permanent wavi-ng of the women of America. Today over 50% of all permanent waving is done by the cold process, and it has been esti- mated that between 25,000,000 and 30,000,000 permanent waves will be given professionally by the cold waving process during •946. Permanent waving accounts for approximately 60% of the income