•/?!•.:i:!]•educing reaction,, miniraising of gS•:•:•::-in'ury risk, and avoidance of bleach •O:•:•=:•i,'mg. T •s development opens up a •f•'"new •eld of investigation for the -•(•::m•ufacturers .... of permanent waving •%solutions, possible lines of approac• •..•.:,:to which have been conmdered .•-•:•,. el•where. '}•)•:?::{•:' REDUCING AGENTS AS • :•[[:½ '• DEPILATORIES :z•?'?-?•:AlkMine reducing agents con- :stitt imporant :}•)?tories, calcium and strontium sul- [Phides being long-established mater- In aqueous solution these dompounds are hydrolysed. to give phide and hydroxide, the :latter playing an important role in •/mmnta]mng the solution near •H 12.. :[Hydrosulphide reduces the cysfine ?disulphide linkages of ker•tin •nd •[:(•.:in the presence-of alkali, swelling .?ji and softening of the fibre takes place, )•'::•'So that after 4 to 5 minutes' treat- ? :'•.ment with a correctly formulated !})•(:depilatory the hair can be wiped from the skin •th a damp cloth. ?•:•.AlkMine solutions of mercaptans, '•::•:•:: such as benzylmercaptosulphonic •:'/•. acid or ethyl mercaptoaniline have (?' been patented as depilatories,•* while /•:. ::•calcium thioglycoHate • is the basis of several nationally advertised pro- ducts. Calcium thioglyco•ate exists. •:-:•:': in two crystalline forms correspond- ing to the formulm ::• •:•: (SH.CH•.COO) •Ca. and •'•:::• S.CH•.COOCa• 3H•O The second fore. is preferable owing to lack of odour and absence of unde- ':: DISULPHIDES AND MERCAPTANS IN HAIR CHEMISTRY sirable effects on perfumes." .It' is used in concentrations of 4'to 10 '•er cent, the commercial.product % being brought to pH 12 by inclusion of free lime. Depilation times are of the order $ to 10 minutes. Addition oi pro-oxidants such as the soluble salts of copper, manganese and iron is stated to give better and' 'safer thioglycollate depilatories. a, All the products described so. far have functioned in an alkaline medium of about pH 12, but a departure from this general class has been described in the Demuth patent which Uses• guanidine thioglycollate or calcium thioglycollate and guanidine, th• pH of the reagent being kept below 10 by hydrazine sulphate2•. In conclusion, it remains to 'say that formulation of depilatories is beset with many difficulties, such as the choice of a satisfactory filler, '-sele•t'i6h $f 'a Su{{a•'[e perfu•e['•'the prevention of separation and the inhibition of drying out. These matters,. however, fall outside the scope of this discussion. ß REFERENCES x Stoves, Nature, 1943, 151,:' 30•1: Proc. Roy. Soc. oedin., 1945, 82, 132. • Stoves. f. Int. Soc. Leat/•. Trades Chem. 1948, 3g, 254. ., * Stoves. La Parfurnerie Moderne. 1951. 27 f. Soc. Cos. Chem., 1951, g, 158. ½ Dawbarn. ß Aust. f. .Expt. Biol. ]Pied. Sci., 19a8, 16, 159. • Toennies..J. Biol. Chem., 1940 182, 455. s Brown and du Vigneaud. J. B•ol. Chem., 1941, 187, 611. ß Kilmer, 'du Vigneaud et el. J. Biol. Chem., 1944, 154, 247 155, e45•. s TarveT and Schmidt. 'J. Biol. C.h•m. 1939. 180, 67. ..

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