252 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS DR. J. J. MAUSNER: I was very interested to see your results with lanolin. This has been used in this industry as an occlusive par excellence for many years and it is somewhat surprising to see that you have recorded total non-suppression with anhydrous lanolin. Could it be possible that these results might be changed or possibly reversed in the presence of other ingredients such as •vater for example, or in an emulsified system? THE LECTUREm They certainly would be altered but i can not conceive that they would be reversed we know that soft white paraffin is almost completely hydro- phobic. Lanolin can be mixed with water and water-containing systems, and I would think that it is physically possible to explain the movement of water across a lanolin barrier. I agree that both emulsifying ointment B.P. and lanolin have been regarded as being occlusive in the past I think it is a little surprising how completely non- occlusive they were under the conditions of this experiment. De. D. SPRUYT: I suggest that you measure the water vapour loss through lanolin, calculate the resistance and you will get your answer.

j'. Soc. Cosmetic Chemists 20 253-263 (1969) ¸ 1969 Society of Cosmetic Chemists of Great Britain p-Benzoquinonediimine - A vital ' ' dy' intermediate in oxdative hair enõ j. F. CORBETT* Synopsis--While it is almost certain that p-benzoquinonediimine is the vital intermediate in oxidative hair dyeing, kinetic studies indicate that it is unlikely that its formation can be unequivocably demonstrated under the conditions pertaining in the dyeing process. However, spectrophotometric studies show that the diimine is formed during the in vitro oxidation of p-phenylenediamine by molecular oxygen. Furthermore, studies of the oxidation of dilute solutions of p-phenylenediamine, in the presence of rn-phenylenediamine, with hydrogen peroxide at pFI 11.2, support the hypothesis that the diimine is an intermediate. INTRODUCTION In a recent lecture (1), I reported that indirect evidence had been obtained to indicate that p-benzoquinonediimine {II) was the vital but short-lived intermediate in the oxidative dyeing process. I also stated that kinetic considerations indicated that it was unlikely that the presence of the diimine would be detectable under practical dyeing conditions. In a subsequent paper (2), Tucker referred to this latter assertion and stated that Dolinsky {3) and Brody {4) had both detected the diimine during the oxidation of p-phenylenediamine (I) with hydrogen peroxide. Tucker thus concluded that its presence had missed detection by our analytical methods. In fact, Dolinsky (3) did not report the detection of the diimine, either "in the precipitate or in the solution". He did, however, isolate a compound to which the structure 2-{4'-aminophenylamino)-5-hydroxy-1, 4-benzo- quinonediimine was assigned, but this does not demonstrate that the simple diimine was formed. In view of the importance of this question to the proper understanding *Gillette Research Laboratory, Reading, Berks. 253