638 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The possible impurities in the Reference Substance, which are unlikely to be revealed by the above tests at the level of purity expected of the material, were hydroquinone, 4-methoxyphenol, 3-t-butyl-4-methoxyphenol, 2-5-di-(t-butyl)-4- methoxyphenol (di-BHA) and 3,3'-di-(t-butyl)-2, 2'-dihydroxy-5,5'-dimethoxybiphenyl (bis-BHA). The Reference Substance was therefore examined more critically by thin-layer chromatography and gas-liquid chromatography. Thin-layer chromatography. The system used was that described in the B.P. 1963, Addendum 1964, which is based on that of Seher(1). At the loading required 5ffthe B.P. monograph (0.2 mg), only the spot due to 2-t-butyl-4-methoxyphenol was detectable. When the loading of the Reference Substance was increased to 1 mg, a spot corresponding with that of bis-BHA was detectable in addition and estimated :as equivalent to 0.01 per cent in one laboratory and 0.02 per cent in a second. In one laboratory, a spot corresponding with that of di-BHA was just detectable and esti- mated at 0.01 per cent or less. No spot corresponding with hydroquinone, 4-methoxy- phenol or 3-t-butyl-4-methoxyphenol was detectable by either laboratory the contents of these impurities (if present at all) in the Reference Substance were thus assessed as less than 0.01 per cent, less than 0.02 per cent and less than 0.1 per cent, respectively. When estimating the concentrations of the impurities present from inspection of these thin-layer chromatograms, it was appreciated that the absence of the main constituent, or the presence of varying amounts of it, may give rise to modified spot areas, leading to false evaluation. Gas-liquid chromatography. The Reference Substance was examined using the conditions detailed below, which gave maximum sensitivity with the apparatus used. Sample size: 10pl of a solution containing 1 g of Reference Substance in 1 ml of benzene. Column: 12 ft glass U-tube containing the 60-80 mesh fraction of 60-100 mesh, acid-washed Embacel kieselguhr impregnated with 15 per cent w/w of Embaphase silicone oil. Column temperature: 180øC. Inlet temperature: 310øC. Carrier gas: Hydrogen. Detector: Flame-ionisation. With thi• system, 3-t-butyl-4-methoxyphenol, hydroquinone and bis-BHA are not detectable. 4-Methoxyphenol and di-BHA are detectable at levels of 0.002 per cent and 0.005 per cent, respectively (by peak-area comparison), but were not detected in the Reference Substance. One unidentified impurity (not revealed by bin-layer chromatographic examination) was detected however in the Reference Substance and was estimated as about 0.001 per cent (expressed as 4-methoxyphenol). CONCLUSION. From these tests, it is concluded that the British Chemical Refer- ence Substance 2-t-butyl-4-methoxyphenol contains not less than 99.85 per cent of 2-t-butyl-4-methoxyphenol, together with a total of not more than 0.15 per cent of impurities, all but one of which have been characterised. t•EFEI•ENCE .(1) Seher, A. Fette Seifen Anstrichmittel 61 345 (1959).

Book reviews LECTURE NOTES ON DERMATOLOGY. B. Solomons. Pp. viii + 249 + Ill. (1965). Blackwell Scientific Publications, Oxford. 2!s. The author's preface states that this is an introduction to dermatology for students and general practitioners. Dr. Solomons would not have been much concerned with its value to cosmetic chemists but this review is naturally influenced in this direction. There is no question of whether the book is a useful guide to "do-it-yourself" dermatology for chemists this is not so much to be eschewed through subservient reverence for the closed shop of medicine as in recognition of the absolute necessity for clinical experience as a background to proper appreciation of a medical text. Lacking such experience, is there any benefit to be gained by a chemist reading a dermatological textbook ? Within certain limits, your reviewer believes that there is indeed. To conduct research on or to manufacture cosmetics, it is surely vital to have some idea of the good and bad effects that products exhibit on the skin insofar as unfavourable reactions may be coincidental or directly related to the topical application, the investigator ought to have some notion of the possible consequences and of the indications for calling upon expert clinical advice. Studying the relevant sections of a fairly elementary book on dermatology, such as Dr. Solomons', will create the right attitude of mind. It would be presumptuous for a non-medical reviewer to criticize the strictly clinical aspects of this book, but various physiological matters or descriptions of topical treatments are relatively easy to assess. For example, the list of allergens on page 84 is hardly comprehensive but it is doubtless selected for its practical significance. The typical dogma or over-simplification characteristic of a smallish handbook is seen in the statement on page 51 referring to cosmetics "there is no article amongst these substances which cannot produce a dermatitis" br on page 129 which states baldly that tinea versicolor is a fungus infection "due to Microsporum furfur." On page 71, there is the statement that seborrhoeic dermatitis of the scalp is basically an increase in the normal amount of scaling of the epidermis, which is known as dandruff expression of the relationship in this manner is at least of dubious validity. Dr. Solomons' book is, as suggested above, concisely written in a style avoiding obscure and highly specialized phraseology. It is well produced and has an exceed- ingly fine collection of photographic illustrations. ESSAYS IN BIOCHEMISTRY. Vol. !. Editors: P. N. Campbell and G. D. Greville. Pp. xi + 170 q- Ill. (1965). Academic Press, London and New York. 18/6. This is the first of a projected series of volumes containing essays on bio- chemical topics. The audience for which the book is designed comprises mainly 639