JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS content of such hair. The latter observation was confirmed by analy- sis of black and white fur from the skunk (Mephitis rnepMtis) and cat (Fells rnaniculata domestica). There is reason to believe that inter- or intra- molecular chelation complexes are being formed by reaction between the iron salts and the melanin, the phenolic groups known to be present in melanin being most probably involved.* HAIR CHEMISTRY The action of alkalis, reducing and oxidising agents on hair is of immedi- ate interest to the cosmetic chemist owing to the use of such reagents in waving and bleaching practice. Alka- lis and bisulphites were widely used as assistants in high temperature waving where they give rise to fission of cystine disulphide linkages. As a result of this cross linkage break- down, the hair fibres are readily deformed and subsequent re-forma- tion of new bonds in the stretched fibre fixes the hair in a permanent wave. The mechanism of the secon- dary reaction following initial hydro- lysis brought about by alkali has been discussed in detail elsewhere. 4,•5 R.S.S.R. q- HzO - R.SH q- R.SOH Alkalis such as borax, carbonates, phosphates, ammonia or ammonium salts were employed in high tempera- ture waving for many years. The * Since this lecture was given the author has elaborated this point and given evi- dence in support of the view that oxidafire polymerisation of 5: 6 dihydroxyindole occurs via the 4: 7 positions. •* t After this lecture was given reviews of advances in cold waving appeared?, •' growing interest in cold waving based on reducing agents of the thioglycollate type, however, has caused them to be less widely used. Nevertheless, a recent patent has described a combination process which is claimed to possess advan- tages over the usual cold waving systems and over the hot systems which involve generating steam in a tress of hair wound upon a curler. The new method consists of winding a tress of hair on a cutler, treating it before, during or after winding with a cold waving reagent of the t. hiogly- collate type, and applying to the tress a chemical heating pad con- taining potassium permanganate, so formulated as to subject the tress to a tepid heat and give the desired waving effect. In the typical two solution cold waving, softening of the hair is achieved by reduction of the disul- pkide linkages. This is followed by rebuilding with oxidising agents. Reduction R.S.S.R --,-2 R.SH Oxidation More recently, one solution cold waving, which dispenses with the use of an oxidising rinse, has been developed. The process is basically the same as in the two solution mercaptan reduction method, but in this case the oxidising rinse is replaced by atmospheric oxidation catalysed by soluble salts of man- ganese, iron or copper manganese chloride being most effective w/th thioglycollates and cobalt chloride with the less used sulphites.$ 164 ,

tIAIR For long hydrogen peroxide has been the oxidising agent used for hair bleaching. In addition to its action on the melanin pigments, this material causes oxidative degrada- tion of keratin, the extent of which is governed by temperature, time, concentration, pH of solutions, as well as the presence of metallic catalysts. •8 The cystinc disulphide linkage is the main centre of attack, oxidation to cysteic acid groups taking place, e.g., taurine, H•N.CH•. CH•SO3H, has been isolated from the liquor after treating wool with acid solutions of hydrogen peroxide, •' while chromatographic evidence has been obtained of the formation of cysteic acid groups in wool bleached with hydrogen peroxide. TM Inter- mediate oxidation products such as disulphoxides O II R.S.S.R II O may also result from oxidation of the disulphide linkage. Catalysis of this oxidation reaction by certain metals is of considerable importance in hair- dressing, since traces of copper, nickel or cobalt present in the hair from earlier treatments, e.g., copper- pyrogallol "rasticks," nickel or cobalt from metallic hair dyes, can give rise to excessive damage. The catalytic decomposition of hydrogen peroxide by salts of copper or iron appears to Fe+++ Ho.O• OH + H•O• • HO• + H•O• ---- OH + Fe ++ --- proceed via a free radical mechanism of the type shown at the foot of the page. HAIR DYES Three main types of hair dye have been used at various times, i.e., inorganic, vegetable and oxidation dyes. The first type relies on the deposition in the hair of finely divided metals, metallic oxides or sulphides. A typical example is an ammoniacal solution of silver nitrate which, after application to the hair, is followed by treatment with pyro- gallol. Lead sulphide has also been used as a basis of a hair dye. Copper- pyrogallol dyes depend on the forma- tion of coloured bodies by atmo- spheric oxidation under the catalytik action of the copper. Purpurogallin and hexahydroxy-tribenzoquinone are among the products formed. HO HO CO Purpurogallin HO OH HO OH HO OH o /-- ----=k :N o I-Iexahydroxytribenzoquinone The chief constituent of walnut hulls is juglone, 5-hydroxy-1: 4 naphtha- quinone O II OHO Fe++++ OH-+ OH H•O + HO2 O• + H•O + OH Fe +++ + OH- 165