28 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS a standard solution. This method is said to be one of the best for testing the chemical sensitivity of glasses and gives reliable indications with the common types, in which lack of stability is associated with an excess of alkali. With other types, however, it may be misleading. Some of the earlier methods adopted for the testing of bottles for medi- cines and drugs made use of the sensitivity of alkaloids (or other materials frequently encountered in medicines and drugs) to the influence of traces of alkali extracted from the glass, with the subsequent precipitation of the alkaloid itself. The most sensitive of these tests was Kroeber's narcotine hydrochloride test, which was adopted by the German Pharmocopoeia for the testing of medicine bottles. After washing, the bottles are filled with 0.1% aqueous narcotine hydrochloride, bottles of 100 cc capacity to the neck, larger bottles about half full. After standing for one hour, there must not be more than a barely perceptible crystalline separation in the bottle, and no cloudy precipitate or flocculent free narcotine base. This test was critically examined by Turner et al who concluded it to be a quick and satisfactory method which could be carried out in a factory without using expensive apparatus, or a high degree of scientific skill. It was not, how- ever, recommended for inclusion in the British Pharmocopoeia in 1931 on the grounds that the precipitation of an alkaloid salt only measured a change of reaction as did an indicator, so that it was simpler (and presumably of wider application) to use an indicator. The evaporation method is especially applicable for testing chemical glassware, and consists of heating with water or aqueous solution at atmos- pheric pressure. One version has been adopted by the Society of Glass Technology in their "Standard 5-Hour Boiling Test for Medicine Bottles". Six well-washed bottles, after having been warmed with hot distilled water are filled, to the bottoms of the necks, with boiling carbon dioxide-free distilled water, and closed lightly with copper capsules. The filled bottles are immediately placed in a suitable steam bath at atmospheric pressure, suspended by their necks, and heated for five hours, after which the contents of each bottle are transferred to a tested conical flask and boiled for 15 min. with a known volume of standard sulphuric acid solution. The mixture is then titrated, and the sulphuric acid which has been neutralised by the alkali dissolved from the bottle is calculated to mg Na20. 4 oz medicals are not satisfactory if the Na•O dissolved exceeds 5 mõ. The test was critically discussed by Cousen, who found the reproducibility to be about 0.2 mg Na•O/sq. dcm. and that the chief cause of variation was changes in the rate of boiling of the water. To allow for variability in the area of bottles of the same volume, (4 oz), he suggested that results be expressed as mg Na•O/sq. dcm. of surface, on which basis the above specification becomes 3.3 mg/sq. dcm. It must be noted that the total alkalinity, though reported

PRODUCTION AND PROPERTIES OF GLASS CONTAINERS 29 as Na20, may be due to mixed alkalis, lime and magnesia. There is no doubt that the results obtained by a complete analysis of the solution are un- exceptionable, but such a determination is laborious and the additional information gained from it, rarely worth the labour. In addition, the bottle glass is assumed to contain not more than 1% boric oxide. If this were not in fact the case, the titration procedure would have to be modified. In other variations of the boiling •nethod, glasses are often evaluated according to loss in weight, electrical conductivity of the extract or determi- nation of the total solids extracted, by evaporation of the solution. In this connection it must be noted that the formation of flakes during the tests bears no relation to the alkalinity or conductivity of the solution, and the flakes should, in fact, be removed and evaluated separately. However, the question still remains whether the resistance offered by glass to the attack of water is a satisfactory criterion of durability. The enormous difference between the attack upon optical glass, by buffer solutions near neutrality, and that produced by water indicates that data obtained for water must not be used too freely in predicting resistance to attack by aqueous solutions. Autoclave methods, in which samples are heated with water under pres- sure, have been frequently used, but they give drastic treatment which often rates the chemical durability of various glasses in an order at variance with actual service. Convenience, however, is an important consideration when deciding which durability test to employ, and for pharmaceutical chemists the use of autoclaves is convenient. The autoclave method has therefore, been adopted by many official bodies, such as the British and Swiss Pharmocopoeias, and the American National Formulary and Society for Testing Materials, especially for the testing of containers for injections. The British Pharmocopoeia 1958 Test for the Limit of Alkalinity of Glass prescribes that six containers be filled with acid methyl red solution (corresponding to pH 3.8) and sealed by fusion, or with close-fitting inert closures. After heating at 121øC (15 p.s.i.g.) for half an hour in an autoclave, the solution in none of the containers shall have changed from pink to the full yellow colour of •nethyl red (pH 6-3 or over). Containers are not washed out before testing, unless they have deteriorated in storage after once having passed the test. In that event, washing is carried out internally with 5% v/v solution of glacial acetic acid, and the test repeated. Where possible, the test should be carried out not more than fourteen days before the containers are to be used. Various criticisms have been levelled at the B.P. ampoule test, mainly on account of the uncertainty of definition of some of the conditions. For example, no indication is given of the time factor involved in heating and •cooling the autodave, neither are instructions given as to the orientation of 'ihe ampoules. If the acid test solution gets into the necks it can become