12 THE JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS experiments show that this is not so owing to the extreme thinness of the liquid layer. The result is not surprising when it is considered that the equilibrium between vapour and stationary phase in a glc column must be reached in less than a second, since it is not difficult to obtain 30 theoretical plates in 1 cm length of column. It is possible that the rate limiting step would be transferred to this stage by a relatively small increase in the thickness of the absorbing drop. Choice of liquid for the absorption The magnitude of the equilibrium concentration of volatile matter taken up from the vapour will depend upon the molecular weight of the absorbing liquid. In accordance with Raoult's law the uptake of vapour will increase as the molecular weight of the absorbing liquid is lowered. Phthalate esters were chosen because they are odourless, excellent solvents and readily obtained free from low boiling impurities. Dibutyl phthalate has a relatively low molecular weight and a longer retention time than most, if not all, the known odoriferous substances. The concentration of volatiles taken up by dibutyl phthalate in the experiments with the roses and with the rubbed thyme, is thought to be around 1%. Larger quantities of volatiles can be collected by using the device described in experiment 1, with the phthalate absorbed on a support as in a glc column. The procedure described has the advantage that it is not influenced by water. In the alternative method, a current of air or inert gas is passed over the odour source and then through a short tube cooled in liquid air or acetone and solid carbon dioxide freezing mixture. The resulting con- densation of all the moisture in the gas causes blockages through ice formation and an additional step is necessary to remove the water from the desired volatiles. So far only a limited number of experiments has been made with the new procedure, but these promise much interesting work for the future. ACKNOWLEDGEMENTS The willing co-operation of my colleagues is acknowledged, particularly Mr. B. Jaggers, for the experiments with thyme and Mr. P. L. Williams, without whose assistance the basic experimental work would not have been possible. (Received: 30th January 1970)

THE ANALYSIS OF ODORIFEROUS VAPOURS 13 REFERENCES (1) Flath, R. A., Black, D. R., Guadagni, D. G., McFadden, W. H. and Schultz, T. H. Identification and organoleptic evaluation of compounds in delicious apple essence. J. Agr. Food Chem. 1õ 29 (1967). (2) Teranishi, 1•., Buttery, 1•. G. and Lundin, 1•. E. Gas chromatography. Direct vapor analyses of food products with programmed temperature control of dual columns with dual flame ionization detectors. Anal. Chem. 84 1033 (1962). (3) l•ushneck, D. 1•. Cryogenic injection and chromatographic separation of cigarette smoke. J. Gas Chrometog. 8 318 (1965). (4) Flath, 1•. A., Forrey, 1•. 1•. and Teranishi, 1•. High resolution vapor analysis for fruit variety and fruit product comparisons. J. Food Sci. 84 382 (1969). (5) Newer, W. W. Some considerations in interpretation of direct headspace gas chromato- graphic analysis of food voletiles. Food Technol. 9,0 115 (1966). (6) Clerk Maxwell, J. Phil. Meg. 8õ 185 (1868). (7) Gilliland, E. 1•. Diffusion coefficients in gaseous systems. Ind. Eng. Chem. 9,6 681 (1934). DISCUSSION MR. J. RID•.INaTON: This new technique appears to show considerable promise of practical use in the future, and I note that it has the merit of simplicity, which perhaps is rather unusual these days. You mentioned that it was unexpected that the rate determining step was the rate at which the odoriferous molecules diffused through the air, and what surprised me particularly was the difference in rate bet•veen linalol and a-ionone. I know that the adonone molecule is bigger than linalol, but not that much and I would not have expected such a big difference in diffusion rate. Have you made any calculations on the theoretical side to explain this apparently very large difference in diffusion rate between molecules which differ only slightly in size? THE LECTURER: I think that the biggest difference is in the vapour pressure. The vapour pressure of ionone around 20øC is 0.01 mm whereas the vapour pressure of linalol at the same temperature is about 0.2 mm, i.e. twenty times as great as that of ionone. If you take intermediate compositions of the drop you find that the linalol very rapidly reaches its maximum glc peak height and is followed afterwards by the ionone, as is shown in Table I. I believe it is possible to make a measurement of the molecular weight from the rate at which the material diffuses through the vapour space. If you make a series of chromatograms, you find first of all that the linalol rises quickly to its maximum followed much more slowly by the ionone. The absorbing drop of dibutyl phthalate is very small and it is absolutely essential that it should be small so that diffusion through the vapour phase becomes the rate controlling step. DR. V. KLEIN: Most manufacturing industries at one time or another have prob- lems with regard to odour emanation which in essence are something akin to head space examination problems. Has the technique of determining head space compo- sition been refined to such an extent that it is possible to determine quantitatively and qualitatively odours that might be perceptible to the ordinary nose at the boundary of an ordinary manufacturing unit? THE LECTURER: I am sure that it would be possible in fact in our factory we get a very decided blank if we pass the atmosphere through a tube cooled with liquid nitrogen you can condense quite a lot of material and get chromatograms showing