230 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS REFERENCES • •lerosol •Ige. 2 (October 1957). 102a. 2 Root. M. J. Package t•ngineering. 3 (May 1958). 28. 2 U.S. Pat.: 31,894. 4 U.S. Pat.: 3,723,200. 5 Glass Packer. 3õ (July 1956). 43. 6 Drug • Cosmetic Ind. 79 (1956). 101 7 -packaging -parade. 2!t (July 1956). 59. 6 Shepherd, H.R. Food _Processing. 19 (February 1958). 30. 9 Briston, J. H. _Packaging. •t0 (June 1958). 80. •o Modern _Packaging. 28 (August 1955). 91. n _Packaging _Parade. 2!t (May 1956). 25. t2 Chem. Ind. $•1 (1949). 205. xa Herzka, A. J. Soc. Cosmetic Chemists. 7 (1956). 350, 352. • Aerosol News (Fall 1957) 1. (E.I. du Pont de Nemours & Co. Inc., Wilmington, Del. U.S.A.) t5 G_P-- 1. (Ohio Chemical & Surgical Equipment Co., Madison, Wisc., U.S.A.) • •lerosol •Ige. 3 (July 1958). 18. •? Herzka, A., and Pickthall, J. _Pressurized _Packaging (•1erosols) (1958). 344. (Butter- worths Scientific Publications, London.) DISCUSSION MR. R. M. MUMFORD: What is the pressure in the hair lacquer pack demonstrated, (a) initially, (b) finally, and (c) is the final performance satis- factory ? THE LECTURER: (a) 90 p.s.i.g., (b) approx. 10 p.s.i.g., just prior to the final spray. A Precision break-up spray valve is used and the final spray appears satisfactory to me. DR. W. MITCHELL: Would it be possible to use a silicone resin as an internal lubricant ? THE LECTURER: An internal coating of this type would increase the cost of the container. There are reputed to be some U.S. Patents on such internal coatings •. It is, however, far easier and more satisfactory to tackle this problem via the viscosity of the product. MR. A. G. MCGEE: I have noticed from your demonstration that the spray cone from the break-up spray valve is far wider than from a conven- tional valve. Is this an inherent feature of this type of valve ? THE LECTURER: The spray cone varies with the formulation. But for any given formulation the spray cone from the break-up spray actuator will be wider than from an ordinary actuator' Some of the pictures shown to-night by Mr. Dixon indicated this very clearly. DR. H. W. HIBBOTT: Would it be possible to arrange for the dip tube to move with the liquid ? THE LECTURER: There is a U.S. Patent on such a valve modification, but it is only of use when the viscosity of the liquid is very low.

PERFUMES IN PRESSURIZED PRODUCTS 231 PERFUMES IN PRESSURIZED PRODUCTS j. PICKTHALL, F.R.I.C.* A paper delivered before the Society at the Symposium on Pressurized Packs, on 14th October 1958. The essential requirements of a perfume are discussed, together with the manner in which a perfume may be affected by different types of pressure packs. OUR TRaDITIONaL handkerchief perfume is simply an alcoholic solution of a number of odorous ingredients. Its pressure-packed equivalent exists as an alcoholic solution of odorous ingredients, together with a liquefied propellant, usually of the halogenated hydrocarbon type. To understand just how the different type of presentation (conventional or pressurized) might affect the odour and stability of a perfume, it is neces- sary to discuss the essential nature of a perfume. Blending Despite many recent papers on the subject, we are not much nearer to solving the mystery of olfaction. To a limited extent, a perfumery chemist can anticipate the odour which a pure chemical will possess. The odour which will result from a mixture of known chemicals is less easy to forecast. If two chemicals of identical vapour pressure are mixed and exposed to the atmosphere, one can in some cases perceive the two odours quite distinctly in other cases one is conscious of a new odour in which neither of the original constituents can be identified. In the first case, one is dealing with chemicals which possess little or no attraction for each other so that each retains its own particular type of odour. In the second case, one is undoubtedly dealing with complex formation due to the physical attraction between the different types of molecules. These forces of attraction will include hydrogen bonding, dipole attraction and van den Waals. In a perfume the concern is with mixtures which contain many separate chemicals, whether of natural origin or synthetically produced, and obviously this question of molecular attraction becomes extremely complicated the poor perfume remaining just a mixture and the good perfume achieving success as a "blend". The ultimate aim in perfumery is to blend together a number of odorous materials and to replace the individual odours by one pleasant impression. * Polak & Schwarz (England), Ltd., Enfield, Middlesex.