40 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS of trial and error, as the following examples show. In various parts of Scandinavia, brown milk bottles are becoming popular, being brought in to el/minate the change of taste caused by over-exposure to sunlight, causing rancidity of the fatty matter. They also afford better protection against destruction of Vitamin C content and against "suntaste", than waxed cartons. Their main drawback is that they absorb heat to a far greater extent than clear bottles do, and thus have to be stored in refrigerators by the retailers. It is also reported that the Swedish Public Health Service has opposed their introduction because it is impossible to see the state of the contents. While borosilicate glass and polythene plastics are recommended for long term storage of all strengths of hydrogen peroxide, ordinary white soda container glasses are not satisfactory, as the alkalis leached from the surface exert a catalytic effect on the decomposition of the peroxide with the result- ant evolution of gas, and build up of pressure in the container. Decomposi- tion is further accelerated by the action of light and as a result, solutions of hydrogen peroxide are normally retailed in amber bottles with adequate headspace (usually 100%). Although decomposition of the peroxide still takes place, and the final result after prolonged storage would probably be the same whether amber or clear soda glass is employed, nevertheless with the latter the short term effect especially in conditions of warm weather, and even where protected from light rays by the use of an external cardboard casing, can be sufficient to cause explosion of the bottle. Some tests carried out at our works on 1 oz soda glass bottles which had failed under these conditions, showed them to have bursting pressure strengths of between 350' and 450 p.s.i.g. which would normally be regarded as satisfactory for the bottling of carbonated beverages, such as beer. Ivanov and I)ochikjan 7 obtained the following figures for the deterioration of 10 vol hydrogen peroxide over a four month period from an original 2.93ø/{, H202 to 0.02% in clear glass 0.48% in amber glass 2.71•/o in paraffin wax lined glass, whether clear or amber. (Received: 17th May 1961• REFERENCES Taylor, W. C. and Smith, R.D. J.Arn. Cerarn. Soc. 19 331 (1936) Dimbleby, V. J. Pharrn. and Pharrnacol. 5 969 (1953) Hughes, D.A. J.Soc. Glass Technol. 42 214T (1958) Turner, W. E. S. et al. J.Soc. Glass Technol. 19 171T (1935) Bacon, F. R. and Burch, O.G. J.Arn. Cerarn. Soc. 23 147 (1940) Lister, W.R. Glass Ind. (September 1940) Iranov, I. V. and Dochikjan, A. Sovet. Farrn. 6 26 (6) (1935)

PRODUCTION AND PROPERTIES OF GLASS CONTAINERS 41 I)ISCUSSION MR. C. BLOOM: I think there is little doubt that the two major dis- advantages of glass are its brittleness and its weight. The weight factor has been very well examined in recent years and as we all know, great improvements have been made but glass will never, of course, compete with plastics in this direction. With regard to brittleness, however, I would have thought that it would pay to investigate this much more thoroughly than it has been, at least as far as I am aware. It is not fully realized that the cost of protecting glass containers during transit is so considerable that a fair differential in the basic price between glass and plastic containers can exist and still make the latter as economical in use. When this differential is reduced even further, the economics of packaging could be very appreciably weighted in fayour of the plastic bottle. The average glass bottle uses only about 1% of the strength of glass. Ordinary glass fibres have a tensile strength of 1 million p.s.i. but the glass is weakened by pits, scratches, chips and abrasions. I would have thought, therefore, that this presents a tremendous challenge to the glass industry. Is there any likelihood of serious inroads into this problem in the near future ? In discussing glass containers, one cannot divorce the closure from the bottle and I wonder therefore whether I may be allowed to make some observations. The selection of a suitable closure, particularly for moisture sensitive products, is extremely important. The key to this problem is the wad rather than the cap, and I have found that a wad of natural rubber is the most effective way of getting a good seal. Rubber seems to be better than cork faced with tinfoil (which provides a seal better than most wads) because it does not itself absorb moisture and because it binds to the glass under all conditions of temperature change. I should warn users that in order to obtain valid information on the effectiveness of a particular closure for a glass container, it is vital to alternate the conditions of storage, particularly with respect to temperature. I have found that whilst butyl rubber and solid polythene wads function well if the temperature does not change, they fail if the temperature of storage is allowed to fluctuate, in both instances due to a high permanent set. Rubber has the disadvantages that it is somewhat costlier than more conventional wads, and that it can impart an odour to the product unless the grade used is very carefully selected. I have found the recently developed polyethylene cone liner to be particularly good for liquid products. THE LECTURER: Glass is very fragile. This fragility can be reduced but you have to pay for it. Glass manufacturers are at the moment