JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS whle the 2-hydroxy derivative Black O p-phenylenediamine .. 2.5 gins. I1 Amino-diphenylamine 0.2 gin. q/x] -OH Ammonia solution (20 ,Nv•N/• per cent) .. 10-0 ccs. II Thioglycollic acid .. 0' 15 gm. O Water up to .... 100-0 ccs. is present in henna and is known as lawsone. Henna also contains some 6 per cent gallic acid, which may be partially responsible for some of the differences in behaviour of henna and synthetic 2-hydroxy-1: 4-naph- thaquinone. Being quinones there seems to be little doubt that juglone and lawsone will actively combine with hair keratin. •'• The main constituent of oxidation dyes is p-phenylenediamine. In certain countries, however, the use of this material is prohibited by law owing to dermatitis risks. Oxidation of p-phenylenediamine procoeds via the aliimine to Bandrowski's Base, which finally gives rise to a black azine. NH• NH N/ II II NH• NH H•NN• / N %/• H,.NNj k Thioglycerol, polythioglycols and thiocitric acid have been used for stabilising oxidation dye formula- tions/• e.g. Blonde p-phenylenediamine .. 1-5 gms. p-aminophenol .. 0'8 gm. Ammonia solution per cent) .... 10.0 ccs. Thioglycollic acid 0'1 gm. Water up to .... I00'0 ccs. Thio-reducing agents are said to make possible the preparation of stable dye creams which do not deteriorate on storage. Oxidation of p-p'-diamino-di- phenylamine gives the indamine, phenylene blue, while p-amino-p'-hydroxy-diphenyl- amine forms an indophenol. H•N--• •-NH-- .__/•X2--0H-- From the oxidation products of o-aminophenol, on the other hand, cyclic structures such as triphen- dioxazine and aminophenoxazone have been isolated. 166

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