THE HYDROLYSIS OF MONOSTEARIN IN AN ACIDIC MEDIUM 711 First order kinetics are apparently followed, though the rate of reaction decreases as the pH of the medium is increased. Ingold found that the rate of hydrolysis of monoacetin at 55øC and pH 4.7 to be about 1 x 10-5 min-1, and that this value decreased steadily as the homologous series was ascended. Extrapolation of his results gives a rate constant of about 6 X 10-6 min-1 which is in fair agreement with that found experimentally. Thus it may be concluded that in any acidic emulsified system based on monostearin, acid catalysed breakdown of the emulgent may be a con- tributory factor in emulsion instability. The reaction, which follows first order kinetics, increases in rate as the acidity of the medium is increased. (Received: 19th July 1968) REFERENCES (1) Jellinek, H. H. G. and Gordon, A. J. Appl. Chem. London, 185 (1951). (2) Patel, M. B. Dissertation Abstr., •0, 3881 (1966). (3) Geltel, A. C. J. Prakt. Chem. 55, 417 (1897). (4) Ingold, C. K., Jackson, A. and Kelly, M. I. J. Chem. Soc., 2035 (1931). (5) Karlsson, K. G. Z. Anorg. Allgem. Chem., 145, 1 (1925). (6) Hartman, L. Chem. and Ind. London, 711 (1960). (7) Averill, H. P., Roche, J. N. and King, C. G. J. Am. Chem. Soc., 51, 866 (1929). (8) Bradford, P., Pohle, W. D., Gunther, J. K. and Mehlenbacher, V. C. y. Am. Oil Chemists Soc., 19, 189 (1942). (9) Jellinek, H. H. G. Revs. Pure Appl. Chem. Australia, •, 139 (1952). (10) Mcllvaine, T. C. J. Biol. Chem., 49, 183 (1921).

j. Soc. Cosmetic Chemists 19 713-724 (1968) ¸ 1968 Society pf Cosmetic Chemists of Great Britain Changes in the composition of vapours over odorous products by permeation through plastic films F. SMIT* Presented at the symposium on "Technical developments in cos- metics packaging", organised by the Society of Cosmetic Chemists of Great Britain, at Harrogate, Yorks., on 26th March 1968. Synopsis--A description is given of the glc method used to evaluate the vapour composition over odorous products preceding, and following, permeation through plastic packaging films. Reasons for the application of a support under the film in the apparatus are specified. The results of the permeation of the vapour over a fruit juice/water mixture through four different plastic films are given. Simplified gas chromatograms show the vapour com- position prior to permeation and after, and charts show the deformation of the composition of the vapour. The changes lead to the conclusion that the components under consideration do not follow Fick's law on permeation. A warning note is given with regard to the influence of the film thickness when comparing different films. INTRODUCTION Many cosmetics and foods are characterized by odour. The odour is thought to be composed of one or more components of the vapours over the product, reaching, either separately or combined, the human organ of smell. Maintaining the odour is equal to maintaining the quality of the product. It is therefore of paramount importance for the packaging material to be sufficiently impermeable to the odour in order to maintain the quality of the product during shelf life. Films, however, differ in their permeability *Central Institute for Nutrition and Food Research TNO, Zeist, Netherlands. 713