THE CHOICE OF PERFUMES FOR PRESSURIZED PRODUCTS 401 this rather drastic test then one can be pretty certain that it will be satisfactory over a long period of time at normal temperature. In our opinion, the advantages of the higher temperature greatly outweigh the disadvantages. MR. S. J. BUSH: Is there any evidence that the irritant effect of sen- sitisers is increased when used in pressurized formulations? THE LECTURER: Unexpected nasal effects have already been referred to. We have no evidence that the effects on skin are different by virtue of applic- ation from pressure packs. MR. J. PICKTHALL: There seems no reason to suppose that irritation properties in a perfume would be increased when sprayed from pressure pack. Although the perfume may leave the aerosol in the from of droplets it meets the skin as a continuous film, and would perform in the same manner as an alcoholic solution applied from a normal container. MR. $. J. BUSH: You mention odour deterioration due to interaction between PVP and perfume components. Have you encountered similar problems with other resins used in hair lacquers? THE LECTURER: Our most extensive work has been carried out with PVP because this has been the most widely used polymer, but we have tests in progress on other materials. It is quite possible that similar effects will reveal themselves. 7MR. G. F. PHILLIPS: What containers are used for the testing of perfumed aerosols for 1 month at 55øC ? THE LECTURER: Many types, but most of our tests have been carried out with tinplate containers of normal design. I expect that you are interested in the leakage aspects, and we do experience some trouble in this respect. Tests affected must be discontinued but at least we learn something even from these. 7MR. J. PICKTHALL: It is not possible to nominate a universal container for these tests. The perfume must be tested in the product itself, packed in the actual container envisaged for final sale.

402 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS AEROSOL PROPELLANTS P. DYSON, B.A., B.Sc.* Presented at the Symposium on "Aerosols", organised by the Society at Southport, Lancs., on 25th April 1965. The major l•rol•er•ies, advantages and disadvantages of the established and the lesser used l•rol•ellants are reviewed. Some detail is also given of work done on the thermal decoml•osition of halocarbons, which has a bearing on their use in aerosols. INTRODUCTION MucI• oF rI•E information in this paper is well-known the object has been to collect it into one place for easy reference. In addition, it is hoped that the paper may put into perspective some of the pros and cons that have often been brandished recklessly by the protagonists of one or other class of propellant. Vinyl chloride has anaesthetic properties, but not at con- centrations remotely involved with its use of aerosols. The chloro- and chlorofluorocarbons can produce highly toxic products on decomposition in naked flames and on red hot surfaces, but it is virtually impossible by using an aerosol to create conditions where this •vould present a hazard to the user. Although it is my personal opinion that the uncontrolled use of flammable propellants could do nothing but irreparable harm to the industry, I feel just as strongly that there is no logical case whatever for a complete ban on the use of a flammable gas as a constituent of an aerosol. Commercial aerosols were first produced in the U.S.A. in 1946, and in Europe and elsewhere from about 1951. Today, some 1,300 million con- tainers are being packed every year and there is no indication, even in the U.S.A., that the market is becoming saturated. Hair sprays have been the best seller in the North American market for some years in the last year for which figures were published, 1961, some 150 million units accounted for nearly 20% of American aerosol production. In the same year, cos- metics as a class-hair sprays, shaving creams, colognes, perfumes and other personal products-comprised about one-third of U.S.A. aerosols, and a similar pattern is rapidly developing in Europe. The majority of the world's aerosols contain chlorofiuorocarbons and the safe properties and high standard of purity of these propellants have had much to do with the public acceptance of aerosols as safe and efficient commodities. Indeed, when the pioneers of aerosols chose the chlorofluoro- carbons as propellants, they did so only after considering the properties of many other liquefied gases they decided that they alone had properties approaching closely to those of the ideal propellant. *General Chemicals Division, Imperial Chemical Industries Ltd., Runcorn, Ches.