CURRENT TRENDS IN COSMETIC PRESSURE PACKS 411 has to be taken into consideration. Corrosion presents no problem if the product itself is safe. MR. R. CLARK: Are there any laws concerning the use of hydrocarbon propellants ? THE LECTURER: Butane is not contained in the Petroleum (Consolidation) Act 1928 because its flash point cannot be determined by standard methods. At present, therefore, there are no regulations against using it. There are, however, local bye-laws concerning filling equipment, etc. For pharmaceutical products which come into intimate contact with sensi.. five membranes, non-chlorinated hydrocarbon propellants are probably far more suitable than the halogenated ones, because of possible hydrolysis. MR. H. S. FORBES: Do you distinguish between corrosion arising from the nature of the product and that arising from the decomposition of the propellant ? THE LECTURER: 2k product which is inherently corrosive to a container, e.g. with a low pH or containing rust promoting substances, will undoubtedly attack the container in its own right. Some propellants, because of their very nature, and possibly in combination with a product, will also attack the container. Sometimes, however, the corrosion may be due entirely to the propellant alone. It is usually difficult to distinguish the two. Many ,theories have been proposed with regard to corrosion by the alcohol/water/ propellant system. MR. H. S. FORBES: Could you indicate reliable tests which can be used to measure lacquer adhesion and how do you interpret the observed results ? THE LECTURER: Lacquer adhesion is usually tested by the rule of "thumb nail" where the lacquer is scratched to see if it will come off. Alternately ,Cellotape is applied, and the ease with which the lacquer lifts on pulling the tape is assessed. When testing various lacquer systems, the container would be cut open in an attempt to make a flat surface out of what is normally a curved one, thereby damaging the lacquer and subjecting it to stresses which it is not meant to withstand. MR. I. DUDLEY: In our laboratory tests, we examine the tinplate as it is cut, apply Cellotape, etc., but it is very difficult for us to define scientifically what we are looking for. We have tried very objective means of doing this, using methods which involved trying to assess the amount .of energy required to remove areas of lacquer from metallic surfaces, but there is no correlation or reproducibility. MR. W. 2k_. WOODWARD: Have you any experience of the "two pack"

412 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS aerosol, the product being in one container and the propellant in a separate container ? THE LECTURER: I have not handled these personally. There are some perfume dispensers of this type in France. These have very complicated valves which increase the cost of the pack considerably. An alternative is the "Jet Pack", which has been licensed to one of the contract fillers in this country. A plastic handle incorporates a nozzle and a container of propellant 12 is utilized. A refillable product container is fitted, and oa operation the propellant passes towards the nozzle, and simultaneously draws up product from the reservoir in fact similar to the old-fashioned perfume atomizer. This type of pack is used mainly for paints. The U.S. Nebu-Halent pack for asthma sufferers is very similar in action. MR. W. A. WOODWARD i In pressurized packs of toilet powders, the particle size must be very important. Could you give us details of the range required for successful formulation ? THE LECTURER: Approximately 325 mesh. It all depends on the valve, and the amount of powder in the container. 8 per cent is the maximum with the majority of valves. I would also refer you to the work of Geary and West [Aerosol Age 6 25 (August 1961)_]. LETTER TO THE EDITOR Sir,--I refer to J. S. Jellinek's paper "Evaporation and the Odor Quality of Perfumes", in page 168 of the April 1961 issue of the Journal. I would like to comment that all these experiments show is that the rate of evaporation is influenced by the composition of the bulk. They do not indicate any reason for this, a/though conjecture is permissible, but fixation is not necessarily a result of molecular association as is advanced in this article. A substance completely inert to one of the smells covering say, -• of the surface of the perfume would decrease the odour concentration or balance of odour to approximately • due to the reduction of the uncovered surface under the conditions of the described experiment and thereby act as a "fixative". The relative factors in fixation are the extent of the surface available to the bulk molecules for their evaporation, the energy of their evaporation and the molecular reflexion properties of the surface, although this latter will not apply to the experiments described. [J. Soc. Cosmetic Chemists 7 69 (1956)5. Yours faithfully, Chesebrough-Pond's Ltd., A.W. MIDDLETON. Victoria Road, London, N.W. 10.