176 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS odorants present, odorants that have structural similarities to the material in question. If, for instance, we add an aliphatic alcohol like linalool to our mixture of heptyl alcohol and benzyl acetate, this should have the same effect as the addition of tridecyl alcohol: it should diminish the vapor pressure of heptyl alcohol more strongly than that of benzyl acetate. We have tried this. Chromatographic analysis of the vapor over a mixture of equal weights of heptyl alcohol, linalool and benzyl acetate indicated that the expected interaction did take place. V^POI• OVER MIXTURE Of EQUAL WEIGHTS OF HEPTYL ALCOHOL ^u• • I•ENZYL AGETATE ¾,• YAPOR 0•R MiXTI/K• Of E'QUAL•EH •TS Of' .-HEf'TTE ALCDHOL, BoeNZYL ^•EYATE A• L INALOOL F•gure,4.--Effect of the addition of a third component on vapor composition of two-compo- nent mixture. Conditions cf. Fig. 3. a. 5 ml. vapor Heptyl alc. 16.2 Peak ratio Benzyl acet. - 5.9 - 2.8 b. 10 ml. vapor Heptyl alc. 3.9 Peak ratio Benzyl acet. - 1.9 -2.1 Mackay carried out an experiment which illustrated the same effect, although it does not involve perfume materials. He showed that the vapor composition over a mixture of equal parts by weight of a number of aliphatic alcohols is drastically changed when water is added to the mixture (Fig. 5). In this instance, water acts as a typical blending agent: it reduces the disparity in the evaporation rates of the alcohols, makes the vapor com- position more balanced and the odor smoother. The interaction between similar odorant molecules not only helps ex- plain "blending" in perfumery, it also brings out the tremendous complexity of perfume creation: adding an odorant to an existing mixture means not only the addition of the odor note due to the new material, but also a change in the balance of the odors of all the other materials present in the mixture!

EVAPORATION AND THE ODOR QUALITY OF PERFUMES 177 EFFECT OF THE MEDIUM ON EVAPORATION RATES In the last experiment discussed, we called water a blending agent be- cause it lessened the disparity between the vapor pressures of the various alcohols, and because it was present in a concentration comparable to that of the alcohols. Had water (as is often the case) been present in large excess, we would have called it a solvent. Yet it would have had the same influence on the ratio of vapor pressures. A "DRY" B "WET" EFFECT OF SOLUTION o._• VAPOR COMPOSITION A = 0.5 cc of vapor from equal volmaes of ethanol, prop-nol, isobutanol, and butano 1 B = one cc of vapor from same mixture in an equal volume of water ArGon Carrier Gas 8 psi 10% Ca.t-bowaX 1500 Column 75øc 1000 Volts Dr. D. A.M. Mackay Evans Research & Development Corp. Figure 5.--Effect of solution on vapor composition. (Courtesy Dr. D. A.M. Mackay, Evans Research and Development Corp.) Two years ago we demonstrated in a series of experiments that the solvent (or more generally, the medium in which the perfume is incorporated) can influence the odor balance of a perfume blend (4). We found that a given mixture of any two odorants usually smelled differently depending on whether it was dissolved in water or in mineral oil, and that in order to