JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The purpose of the present communication is to review some publications relevant to some popular ideas about olfaction and which, it seems clear, are little known or, at least, seldom read. Loss oF WEIGHT BY MUSK It has been known for a very long time that a minute quantity of musk can perfume a large space for many years and supporters of radiation theories of olfaction have consequently suggested that the material emits its aroma without losing weight. Now, on at least two occasions, experiments on the evaporation of solid musk have been conducted and it cannot be claimed that they provide any support for this view. The first of these investigations, carried out by John Aitken and published in the Proceedings of the Royal Society of Edinburgh (1905-6, 25, 894-902), is entitled "Evapora- tion of Musk and Other Odorous Substances." Aitken was concerned to show that the odorous particles emitted by musk are in the form of gas or vapour and not, as some had suggested, in the solid form. He drew filtered air over musk (presumably natural musk) into a flask containing a little water. When the pressure of air in the flask was then reduced by applying suction, no cloudy condensation occurred although such condensation was always observed when solid particles (dust) were present. In confirmation of this, Aitken also showed that the odorous material emitted by the musk was not trapped by passage through a plug of cotton-wool. "Loss of Weight of Musk in a Current of Dry Air" is the title of the second investigation which was carried out in 1912-13 by Bazzoni, whose account of the work appeared in the Journal of the Franklin Institute (1915, 180, 463- 469). Using a sensitive micro-balance of special design, he determined the weight of a dried specimen in a current of dry air at intervals during a period of seven months and readily showed that, during this period, a loss of 14 per cent occurred (0.18941 rag. from 1'32245 mg.). Natural musk, of course, is a complex mixture and hence the loss is due to evaporation of volatile matter all of which is not necessarily odorous. PSYCHOGA•.VANIC MEASUREMENT Since nervous emotion is accompanied by changes in the electrical con- ductance of the skin, it has been suggested that the measure of the extent of such alterations might also be a measure of odorous strength and of the degree of pleasure or displeasure aroused in man by odours. About thirty years ago, Auld set out to test this suggestion, but without success (J. Inst. Petrol. Technol., 1923, 9, 889-391). The slight differences in the odours of the petroleum products which he studied were found difficult to record on his "emotion meter" (a simple electrical device incorporating a galvanometer) and when he increased the sensitivity of his instrument, outside influences became so marked that the whole procedure became useless. 208

MORE TRUTH ABOUT ODOUR A few years later, Bijtel and Van Iterson (Arch. Neerland. Physiol., 1925-26, 10, 447-448) published a brief report on the psychogalvanic reflex produced by olfactory excitation. Using camphor, citral, caproic acid, glacial acetic acid, ammonia, cinnamic aldehyde and cigar smoke, they found that quantitative differences could readily be recorded but that there was considerable uncertainty about qualitative differences. These British and Continental researches were followed by an American psychological study in which one hundred adolescent children were examined, fourteen odorous substances being used. The investigators, Coombs and Shock (Psychol. Bull., 1935, 32, 531) divided the odours into three groups-- pleasant, least unpleasant and most unpleasant--and also studied odorous strength. The tentative conclusions which they reached were: first, that the affectire quality of the stimulus must be considered as well as the affectire strength as a factor determining the magnitude of the galvano- metric deflection and, second, that for equal degrees of affectire strength, unpleasant stimuli tend to give greater deflections than pleasant stimuli. Psychogalvanic procedures seem to have been adopted on at least one other occasion although there is some doubt about the scientific status of the "investigations" concerned. The subjects were film stars from Hollywood and the instruments employed were the "psychogalvanoscope" and the "electro-oleo-convector." Perhaps the chief value of the experiments con- ducted with these devices lay in the delightfully ironical comment which they elicited from the French writer who described them in Parfumeri• Moderne (1930, 24, 335 337). "Nous serions f•ch•s de jeter une ombre, m•rne l•g•re, sur ces illusions juveniles l'Europe n'est pas mfire pour les r•v•lations de l'•lectro-psycho- olfacto-galvanoscope, pas plus que pour celles de l'•lectro-oleo-convector. Les Francaises, notamment, n'ont besoin d'aucun outillage • lampes d'amplification pour vibrer plus ou moins agrdablement sous l'influence de tel ou tel parfum qu'aucun appareil ne leur fait choisir' leur go•t affin• leur suffit." DISSOLUTION IN AIR Continental workers on olfaction sometimes refer to the "solubility" of odorous substances in air and, indeed, it has even been claimed that, in order for a substance to be odorous, it must possess such solubility. Although it appears certain that there can be no specific solubility of one gas or vapour in another, it is perhaps not impossible that odorous substances behave towards air in a way not shared by materials which are devoid of odour. In this connection, the experiments of Erdmann (J. prakt. Chem., 1900, 109, 225-228) are most interesting. He decided to study the solubility of odorous and inodorous substances in liquid air and found that whilst ether, alcohol, water and carbon dioxide are practically insoluble in that material (they solidify and can be removed by filtration), odorous substances such as c itra 1 209