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

PERFUMES IN PRESSURIZED PRODUCTS 235 introduction of hydrochloric acid are magnified by traces of metal even if the metal is present only in the perfumery constituents. The • problems which arise in producing a stable perfume for use in metal containers in the presence of trichlorofluoromethane are great and, without a doubt, many of our normal ingredients are quite unsuitable for this type of product. Supposing we packed in glass an existing handkerchief perfume under the most favourable of pressurized conditions, say, Per cent Alcohol 47.5 Dichlorotetrafluoroethane 47.5 Perfume 5.0 If we are concerned with smelling the perfume only from a surface, then what would be its stability compared to its equivalent in the non-pressurized bottle ? While the answer well differs from perfume to perfume, in the main, there will not be a great difference between the two types of packaging. After one year the pressure packed perfumes seem to take on a rather sharp ester-like note and in some cases terpenes tend to produce "off" odours. One other effect is the formation of an acetal odour. This latter effect (the production of diethyl acetal of acetaldehyde) undoubtedly occurs in the presence of alcohol and easily hydrolysed propellants. [Received: l•lth October 19581 DISCUSSION DR. B. L. RAo: Can gums and resins be used as fixatives for perfumes in aerosols ? THE LECTURER: The resins may be used for their odour and fixative properties just as in normal types of perfumes. The question of valve clog- ging has been somewhat over-emphasized. Nevertheless, it is a wise pre- caution to use resins which have been extracted with special solvents. DR. B. L. RAo: May crystalline materials be used in aerosol perfumes ? THE LECTURER: Yes. The question of solubility must be solved as with a normal alcoholic perfume. In other words, the perfume containing the crystalline ingredients must be tested in the presence of both alcohol and propellant to ensure that no precipitation takes place on standing.