PERFUMES IN PRESSURIZED PRODUCTS 233 recommendations made in the literature. This is not sales talk, but common sense. One of the most common mistakes made in pressurized perfumery is to consider handkerchief perfumes and toilet waters as space sprays. They can, of course, be sprayed into the atmosphere, but normally they are applied to surfaces such as skin or fabric. Even apart from considerations of price, it is often an advantage to include water in an alcoholic perfume, particularly where colognes are concerned. In the pressurized product it is difficult to include as much as 15 per cent of water. With higher amounts, problems of miscibility with the propellants arise. It has been stated many times that a given amount of perfume in a pressurized system will produce odour effects many times stronger than those given by the same amount of perfume in a non-pressurized system. This increase in strength of odour only applies to a solution examined in the form of a fine spray, which is not the way we normally use our perfume. It is more realistic to retain the normal amount of perfume relative to the alcohol and to ignore the propellant as a constituent. After all, if we use 2 per cent of perfume, 31 per cent alcohol and 67 per cent propellant, and spray this on to a surface, the propellant is almost immediately lost and we are left with a 6 per cent solution of perfume in alcohol. Another misleading statement which occurs in the literature is the suggestion that drastic differences in odour are to be found between pressure packed perfume and conventional packs. Take an alcoholic solution of a perfume and divide it into two portions. Place one in a normal bottle and a second in a pressur- ized bottle together with propellant. If these two solutions are applied to at surface, in less than no time the propellant is lost from the pressurized type and one is left with two identical solutions which, if smelled, give the same odour impression. It is only when the pressurized solution is sprayed into the atmosphere and smelled that the odour effects are different. It is therefore necessary to appreciate the difference between a space spray and a surface spray, and many writers have assumed that handkerchief perfumes and toilet waters are sprayed into the atmosphere, and not on to surfaces. if the perfume is in fact space sprayed, then drastic odour effects caa indeed be expected. When sprayed, loss of propellant can be presumed and small particles of alcohol and perfume are left which strike the recep- tors of the nose partly in 'vapour form, but also in liquid or condensed form. Not unnaturally, the odour effects differ from those appreciated when smelling the perfume in vapour form from a surface and, of course, the possibilities of irritation are considerable. There is no doubt that a perfume giving a well-blended effect whea smelled from a surface may give very different odour impressions in the spray form. Many perfumes make use of one particular ingredient around which the general bouquet is built. Properly formulated, this one

234 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS ingredient remains discreetly in the background and cannot be separately identified. This same perfume when sprayed may well be completely domin- ated by this particular chemical. On the other hand, the effect of that one chemical may be greatly diminished and become secondary to other odours. In other words, the whole balance of odour may be disturbed by this new method of presenting the perfume to the nose. Two important ingredients in perfumery are alcohols and their esters, and if blending has been well effected, then there will be an equilibrium between these two. When smelled in the form of a spray, one or the other of the two chemicals tends to predominate. Sometimes the ester note is too greatly in evidence, some- times the alcohol. It depends upon the type of alcohol and ester involved. Even more important is the effect produced by the strong ingredients normally used in small amounts or even in traces. Very valuable effects are obtained by traces of civet, phenylacetic acid, phenyl acetates and other strong and, perhaps, unpleasant smelling materials. Properly handled, these give no unpleasant odour effects in a normal perfume, but if smelled in spray form they may leap into prominence and produce extremely disagreeable odours. Many of our perfumery raw materials contain "impurities" which are not harmful in our normal perfume and may, in fact, be of value. Such impuri- ties may well be over-emphasized when space-sprayed and it is often neces- sary to work with very pure chemicals and specially processed essential oils. In summary, it can be said that if a pressurized perfume is to be surface- sprayed, then normal blending techniques can be followed, but if space- sprayed, then a completely new approach is required. It has been said that the result of a fine spray is excessive volatility of the perfume. This is an exaggeration, the effect of producing a droplet size of 30 or 40/• means very little increase in vapour pressure. I must emphasize at this stage that I have so far discussed the perfume when freshly packed. The effect of storage in the presence of a halogenated chemical is a very different matter. A study of the literature dealing with the effect of the propellant on the odour of a perfume is not very rewarding and certainly leads to some con- fusion. Some writers see only beneficial conditions, others suggest the worst. In the first place, it is suggested that in the absence of air, the alcoholic solution of perfume just cannot deteriorate. In the second place, the adverse effects of hydrochloric acid are emphasized. To try and put the case in a realistic manner, I believe that not too much faith should be placed on the beneficial effects of excluding air. The effects of hydrochloric acid developed by hydrolysis of the propellant are at a maximum with trichlorofluoro- methane, much les,s with dichlorodifluoromethane and at a low minimum with dichlorotetrafluoroethane. Changes in odour brought about by the