44 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS found that a cheaper grade of a given aromatic will appeal to the perfumer much more than the highly refined expensive grade. A hard-and-fast rule cannot be laid down, but one can safely say that a low price is not always an indication of a poor product, and a high price does not always mean an aromatic which is most suitable for your purpose. Let me then briefly summarise. The perfumer requires certain aromatics in the chemically pure state. These are mainly isolates, but also certain synthetics. He requires other aromatics in an impure state, speaking from the point of view of the chemist. Furthermore, one perfumer insists on a large proportion of impurity to be present, another perfumer demands the same aromatic with as little impurity as possible. But all perfumers agree on one aspect: to get the product they want for the lowest possible price. So the manufacturer, as I have already said, has to offer different grades of one given aromatic, different in odour quality and in price. But the number of grades he can afford to offer is naturally limited, and so he, too, has to come to the well-known conclusion that it is impossible to satisfy everybody, the reason in this particular case being the element of personal preference, both olfactory and economical preference, that is always present in the evaluation of certain aromatics. So, after having decided on the number of grades of a given aromatic and on the physical and chemical specifications with which they will have to comply, the manufacturer must adopt this principle: to produce his different grades of aromatics in a consistent olfactory quality. Only then will the perfumer be able to rely on a supply of perfumery chemicals which have a degree of purity that meets his requirements. DISCUSSION Mr. Pickthalt: Referring to the speaker's comments on trichlor phenyl methyl carbinyl acetate, I think it is well known that the typical rose odour develops on standing. Nevertheless, I believe that even the most highly purified laboratory sample still retains a definite odour. Author: In my opinion this may be a matter of personal judgement. It is a fact, however, that when the ester is crystallised the odoriferous "impurity" goes into the mother liquor and can be isolated. I have prepared an "odourless" sample of the ester. Mr. Pickthalt: On the subject of a perfumer's idiosyncrasy on impurities in a raw material, I should have thought the manufacturer would have had less trouble in producing relatively pure synthetics than would be the case with isolates. With the latter one is forced to use nature's starting material, and separation of the constituents by distillation is often extremely difficult. In synthetics the manufacturer can use his ingenuity to produce a chemical which, within the meaning of the word, is "pure."

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.