DROP TESTING OF PLASTIC CONTAINERS 15 shock. If you could drop them so that they hit firmly on the corner you would prob- ably get a good result. MR. C. E. Hm•s: In relation to orientation of drop, I am absolutely convinced that there is a major difference between dropping onto the bottom and dropping onto the flat - I do not accept that dropping onto the bottom is the most severe condition. I am surprised that nobody has referred to dropping on the cap because the shoulders are so frequently a source of potential problem. I would like to suggest that when one drops a bottle which has a pronounced difference between the minor and major axis onto its large, flat face, one gets, what I believe is called in America, 'hydronamic hammer', and one imparts a shock to the liquid which encourages it to flow violently at right angles to the plane of impact. Thus one will tend to knock out the face and knock off the shoulder, and one is therefore imparting a shock to the bottle which is diametrically opposed to the shock that it received when dropped onto its face. In relation to viscosity of the product I entirely endorse what you have said. I believe that it is unconforming to test with water, because one always suspects that one should test with the product, but whenever I have tested in strictly comparable series, between product and water, I always come to the conclusion that it was very reasonable to use water. I believe that 10 ø is very reasonable for testing, but I believe it is important to remember that bottles are frequently stored in quite a cold cellar and might be brought on to the production floor very cold. They can be well below 5 ø, and when first being filled in these conditions there is little doubt that they are probably in their most sensitive state. '['}•, Ll,:cTum,zu: Your comments are very useful indeed. Our bottles are closed with a long polythene top which would cushion the impact quite well, and it would therefore be unrealistic to drop them onto the top. Our factory storage is heated so we do not have that problem which you mention. Mm R. J. Fom.•t•s: I believe that in Scandinavia they use higher impact grades (luring the winter. MR. L. G•T•D: [ think it is important to remember that some people may be packing liquids with a very much greater density than water, and that the load inside a bottle can be very high. I have experienced considerable problems of container breakage with a sugar syrup. The water drop tests did not reveal the problem but dropping with the product did. Admittedly we were not doing these in PVC bottles but the differ nee of the weight of the contents was a point that we had to note. MR. D. B. VI•c•: What part does the ullage play? I would rather have thought that the larger the ullage the more the liquid would be free to move, and the more the hammering effect at the time of impact. Yet you mention worse results with a gel? TH• L•C•URF. R: My comments on the gel are based on very little experience but we have looked at a few containers with gels and they did seem remarkably fragile, and they do transmit shock rather well. I have not studied ullage systematically on our container but when investigating sachel strength in the past, this was an important point and I see no reason why it is not here. I do not know, however, whether there is a critical level.

j. Soc. Cosmetic Chemists 20 17-29 (1969) ¸ 1969 Society of Cosmetic Chemists of Great Britain Principles of corrosion of metal containers by cosmetic products D. M. HOWARD* Presented at the symposium on "Technical developments in cos- metics packaging", organised by the Society of Cosmetic Chemists of Great Britain, at Harrogate, Yorks., on 27th March 1968. Synopsis--Mechanisms of corrosion reactions are briefly surveyed, and several experimental methods of finding corrosion rates are summarised. The use of those which have been found to have application to packaging problems are described and methods of approach to such problems are indicated. INTRODUCTION The problems set by the tendency of metal containers to be corroded by their contents are not easy to resolve, for not only are there a variety of different metals and alloys used in packaging, sometimes in contact with each other, and in varying states of purity and stress, but also the sub- stances which they are expected to hold are often mixtures of a complex chemical nature. Our object in initiating work on corrosion was to obtain more knowledge of corrosion processes in general and, in particular, those liable to occur in metal containers, especially aerosol cans. It was hoped that insight into these processes would lead to a reduction in both the size and duration of the storage tests for new products and containers, and would also provide means of solving the corrosion problems which arose. Two steps were necessary for the achievement of this object. Diagnostic experimental techniques had to be developed so that the rate of corrosion of a container *Pack Development Laboratory, Reckitt & Sons Ltd., Hull, Yorks. 17