TALKING OF PERFUMES AGAIN discuss. A layman with a tune running through his mind might hum or whistle the tune and enable a pianist to record his impressions. One could likewise describe a scene or subject to a painter and comment upon colour depths and tones so that the impression could be translated and recorded. When one acknowledged perfumer speaks to another equally accomplished in the art, even they are sadly deficient in descriptive phrases and the jargon they employ would be Greek to an outsider. We speak of top, middle and back notes, intended to convey a scale of diminishing volatility of the con- stituents. This same scale is also employed on a weight basis•light, medium and heavy notes. We speak of warmth of odour, but what does that mean to the layman, and just how closely would two perfumers agree on a tempera- ture scale in describing a range of chemicals or oils ? We limit our use of colour comparisons to green, a word intended to be descriptive of odours associated mainly with leaves, but how green is my Lily of the Valley ? We make half-hearted use of linear measurements and talk vaguely of "depth." Naturally, we bring "aromatic," "aldehydic," "phenolic," "fatty," "burnt," "leathery" and a host of partially descriptive names into our con- versation, but again the values are vague and uninformative to the outsider and far from definite to the expert. After all, there are a great number of aldehydes, to name but one word from our dictionary. We come nearer to reality when we speak in terms of flowers, for despite the variety of odours to be found in one floral type, the naming of Lavender, Rose or Carnation is certainly descriptive, although even the use of floral names is limited to a relatively few well-known types. This frustrating lack of vocabulary brings to mind a story which I am sure will be familiar to all members of the audience. It concerns Noah and his Ark and, incidentally, Noah must have had his problems where odours are concerned. The story goes that Noah named his animals with little or no effort, until he came to the frog, which completely stumped him. Asking his wife's opinion, she immediately said, "Call it a frog," and when Noah asked why this particular name, Mrs. Noah replied, "Because it looks like a frog." Admitting, therefore, our lack of vocabulary, how are we to rectify this inadequacy ? Obviously, by establishing a scale of units which will accurately and precisely describe a given odour, but before such a step can be taken we have still to investigate and understand just exactly what odour is and how it works. ODOUR PERCEPTION This phenomenon constitutes a scientific miracle. The ear and eye cater for a relatively small number of vibrations but the nose can receive and identify an apparently unlimited number of different odours or, at any rate, relay messages which the brain translates as differences. Many theories on 183

JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS odour have been put forward and, in the main, they can be divided into two classes--the chemical or corpuscular and the physical. The latter school of thought suggests that odorous substances radiate high frequency vibrations and that differences in wave-length are responsible for differences in odour. To some extent these ideas were founded on the false assumption that certain chemicals emitted odour for long periods of time without loss in weight. Thus natural and synthetic musks were said to be capable of transferring their odour to grease-smeared surfaces without weight loss, when exposed to the atmosphere. These experiments reflect upon the inadequacies of our weigh- ing equipment, although one must bear in mind that 1 gm. of Musk Ambrette is theoretically capable of releasing 2.7 x 102• molecules, and that one "sniff" will bring odour response when as little as 0.00000000025 gms. of natural musks are present in the air and, perhaps, ten times this amount of synthetic musk. I was rather intrigued with the little item from February International Perfumer. This note mentions Eugene Rimmel's extraction of odorous materials from petals by means of volatile solvents and is a quotation from his book, written nearly 100 years ago. Mentioning that the process had not been put to any practical application on account of expenses, he finishes as follows: "It has, however, served to prove the imponderability of fragrant mole- cules, for although this substance from its high state of concentration appears at first sight to be the solidified principle of scent, after it be treated several times with alcohol, it gradually loses all its perfume, and yet the residue is not found to have lost one atom of its weight." I think we can accept the fact that odorous substances release molecules which are air-borne to the nose and that with some substances a quick intake of breath or "sniff" is required to provide the necessary concentration of molecules to evoke odour response. E. D. Adrian writes effectively on the subject in his "Flavour Assess- ment" in Chemistry and Industry, November 28, 1953, and describes how the essential step in odour perception may be the contact of molecules with the millions of hairs present in the sensory cells of the olfactory cleft and the surface layer of mucus and water. Just as we can accept volatility as an essential property, so we can include relative solubility in water and lipides. In fact, I like to think of an odorous molecule as a kind of emulsifier, its effect and performance depending upon its ability to overcome tension between surfaces and its relative affinity for aqueous and "oil" phases. This "fixing" of the molecule at the surface or interface could determine the setting of the angles bonding the atoms of the molecule, changes in the bonding angles setting up variations in potential energy. Just how the released energy is transmitted and analysed is another matter. To me the whole mechanism has something of the Hollarith punch-card system. 184