VISIBLE REGION ABSORPTIOMETRY IN COSMETIC ANALYSIS difficulties arose was found in this laboratory in the estimation of trypto- phane by means of p-dimethyl amino benzaldehyde. The method consists in the condensation of tryptophane with p-dimethyl amino benzaldehyde in 19N sulphuric acid over a period of hours this is followed by oxidation to a coloured compound with a dilute solution of sodium nitrite, and the colour is measured after a further time interval. In this determination it was found that the resultant colour was affected (a) by variations in the quantity of sodium nitrite used, (b) by the condensation time, and (c) by the time allowed to elapse before the estimation of the colour it was also found that one of the preservatives added to the product gave a colour with the reagent and, finally, that the intensity of the colour produced by a standard amount of tryptophane was controlled by the reducing properties of the system as measured by a ferricyanide titration. To overcome these difficulties, the following procedure has been adopted 1 ml. of the test substance is treated with 9 mls. of a solution containing 30 mgms. p-dimethyl amino benzaldehyde in 21.1N sulphuric acid: this mixture is allowed to stand in the dark for 16 hours (overnight), then diluted with 5 mls. of distilled water, cooled, and to it is added 1 mi. of a 0.023N solution of sodium nitrite. After standing in the dark for a further 1« hours the colour is measured on the absorptiometer, using an orange filter. By adhering to this schedule the first three variations are eliminated. Having obtained a value for the light absorption, the apparent tryptophane content is calculated from a calibration graph which shows the relationship between colour density, concentration and the reducing properties of the sample. Finally, the true tryptophane content is obtained by subtracting a constant amount which corresponds to the added preservative. This method is now in use as a routine procedure and has given concordant results over a long period. An advantage of many colorimetric methods when compared with other techniques lies in their sensitivity. For the determination of substances present only in very small concentrations few other methods can compare, and this type of determination is likely to increase in importance with the development and application of column analysis techniques of the type used by Moore and Stein 2 in their work on amino acid analyses in which they used the colorimetric ninhydrin method for the determination of the amino acid content of the fractions. Colorimetric procedures are available for many estimations which are of interest to cosmetic chemists: the average particle size of powders can be estimated turbidimetrically•,t while lanolin 5, as in the example above, lead 0, and quaternary ammonium compounds' are only a few of the substances which can be rapidly determined by colorimetric techniques. Many others could be added, but such a list would be out of place here, and enough has already been said to illustrate the usefulness of visible region absorptiometry 181

JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS in the rapid determination of many substances, particularly when they are present only in small concentrations. ACKNOWLEDGMENT The author wishes to express his thanks to the Directors of County Laboratories, Ltd., for permission to publish this paper. REFERENCES • Clark, G. R., y. Soc. Cos. Cicero., 1951, 2,290. '" Moore & Stein, •f. t•iol. Chem., 1948, 176, 367. a Bolton & Marshall, Soap and Sanitary Chemicals, 1949, 25, 129. • Hawksley, B.C.U.t?./t., 1944, 8, 245 (Review). • Lederer & Tchen, Bull. Soc. Chim. Biol., 1945, 27, 419, via •f.C.S., 1949, 2121 6 Anal. Meth. Comm. Rep. Analyst, 1954, 79, 397. ? Fogh, Rasmussen & Skadhauge, Anal. Chem., 1954, 26,392. /t Lecture delivered to the Society on 5th ]kIarch, •r954 TALKING OF PERFUMES AGAIN By J. PICKTHAnr, F.R.I.C.* I•TRODUCTION THERE MUST be a number of non-technical members of this audience who are interested in perfumes and who would like to know something of their nature and the way in which they are employed. Further, many of our technical members use or handle perfumes without, perhaps, having had the opportunity of giving the subject a comprehensive study. Nobody would doubt the importance of perfumes in the cosmetic and associated industries: they are as important to success as attractive packing and presentation. One might add that a perfume continues to please the buyer long after the appeal of the container has faded. Most people in this world are favourably impressed by a good perfume, although naturally preferences are widely divergent. Even the men, although often reluctant to admit it, are influenced by odour. My aim this evening is to introduce perfumery to those who know it only by name, to assist those with a working knowledge and to interest the experts. Perfumery, although one of the oldest arts of expression, is young in a scientific sense. We know little of the mode of action of odour perception and much work of a scientific nature remains to be undertaken before we can develop theories. Frankly, I do not believe that the many classifications offered have greatly helped either the established or the budding perfumer. The well-known numerical classification, I am afraid, confuses without offering a starting-point as a language or even an alphabet for perfumers. It is this lack of descriptive words that makes perfumery so difficult to * Polak & Schwarz (England) Ltd., Enfield, Middx. 182