SOME ASPECTS OF PERFUMERY CHEMICALS 45 Author: This is quite true. But with a natural material the "impurity" is always the same. With a synthetic the kind and proportion of the impuri- ties depend on the process. The manufacturer can produce a chemical which is "pure," but if the perfumer was used to a product produced by a different process and therefore containing an "impurity" he will reject the "pure" product. Dr. A. W. Middleton: With reference to the effect and amounts of impuri- ties in synthetics, has the lecturer any experience with gas chromatographic methods for their detection and estimation ? Author: No. Mrs. H. Butler: Would it not be better for the manufacturers of synthetic chemicals to prepare standardised pure synthetic aromatics on a par with Analar chemicals and let the perfumers get used to them. I suggest that would raise perfumery from the realm of art to science ! Do you agree ? Author: I agree. But perfumers do not want to get used to a "pure" product if they have always been using the "impure" variety for their particu- lar creations. Mr. R. T. Luton: Impurities in synthetics--odour. Is this true for natural products ? Author: Yes. Impurities do influence the odour of natural products. Dr. A. Klein: Do you feel that there is a tendency to overstress the importance of analytical results, e.g., % purity, in synthetics ? It is, after all. relatively easy to produce an extremely pure and yet perfectly flat rhodinol. or linalyl acetate of 99/100% purity which many perfumers would reject in favour of the 90 or 950//0 grade, to mention only two examples. Author: This is exactly the point i have been trying to make in my lecture. As you say, it would be quite easy to make a 99/100% linalyl acetate, and the perfumer may or may not reject it on odour. On the other hand, it is almost certain that the perfumer would reject a sample of linalyl acetate containing 85}/0 ester. So as I have said, the manufacturer has to set himself analytical and olfactory standards. Using always the same method for the manufacture of his product and making sure that the final product conforms with the analytical specification, he may be reasonably certain that the odour of the product will be acceptable to the perfumer. For this reason I do not believe that the importance of analytical figures can be overstressed REFERENCE • W. Mitchell. P.E.O.R., 1950, p. 41.

46 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS SMELL--THE PHYSICAL SENSE A. W. MIDDLETON, B.Sc., PH.D., F.R.I.C.* The sense of smell is shown to be analogous to that of hearing and to be a "physical sense." The fundamental physiological or physical basis o• the different oltactory phenomena is explained, and the explana[ions are a sui[able criteria •or the assessment o• experimental work. A l•lea is made •or the establishment of a co-ordina[ing cen[re for research on olfaction. IN THIS article it is proposed to explain the behaviour of the sense of smell in a qualitative manner and to work out a basis on which quantitative studies can be made. The appropriate inductive approach for the development of a ½atisfactory theory regarding the sense of smell, is: 1. To collect the properly established observations. 2. To consider any information available concerning other senses, and also of the relevant properties of gases. 3. To develop from the whole, consistent explanations of the mechanism of response of the olfactory organs to odorous stimuli. 4. To plan future experimental work in a co-ordinated manner, and to modify the theory as may be required by its results. PART I OLFACTORY OBSERVATIONS TO BE EXPLAINED Basic Odour Research • collects together the work of many authors on olfaction from which the following accepted smell behaviour can be gleaned. (a) Adaptation and Fatigue. Continued exposure to an odour can more or less rapidly lead to inability to smell that odour, without necessarily causing inability to smell other odours: on continued exposure to an odour such as that in the cream room of a cosmetic laboratory, the smell of the perfume compounds in use rapidly disappears, but other odours can still be detected in that room. (b) Anosmia. Persons exist who are unable to smell (or to differentiate between members of) certain groups of odorants whilst smelling others normally. (c) Paralysis. A few substances, of which formaldehyde is outstanding, paralyse the sense of smell to all odours to the same degree. * Chesebrough-Pond's Ltd., London, N.W. 10.