368 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 2. A polythene stopper that will fit a given bottle will fit any number of similar bottles. 3. The fact that they are hollow does minimise air compression in bottle necks. Points in criticism of their use are: 1. Cost.--On this angle it is doubtful if they will ever displace moulded caps or corks also it is very doubtful if they will ever entirely displace glass stoppers. 2. Difficulty of removal.--One hesitates to tackle, as advised, the removal of stoppers with pliers, where bottles of acid are concerned. 13. They are not generally accepted as being efficient for the purpose of bottling volatile solvents. PORCELAIN SWING STOPPERS WITH RUBBER RINGS This type of stopper was once commonly used in the milk bottling trade, but nowadays its use is chiefly confined to the mineral water trade. It is more expensive than other types of re-usable closures, and is not very satisfactory on modern fast and fully automatic bottling lines. It will hold pressures of carbonated drinks quite well, but is now much less popular than in former years. CLOSURE CAPS The following widely used types of closure caps and seals come under this heading: aluminium foil as used on milk bottles, crowns, moulded caps, metal screw on, metal screw rolled on, metal spring or clip on, aluminium foil with cork liner. ALUMINIUM FOIL CAPS These have a firm place in the bottling trade, and are without doubt eminently suitable, because of cheapness and hygienic application, for the purpose of capping very short shelf life and short journey consumer goods, as will be seen in the everyday bottling of milk and orange juice. The main criticism of this type of closure are: 1. Containers on which this is used can only travel upright. 2. This type of seal will not withstand any appreciable pressure. CROWNS These are probably the most efficient common type of closures made, besides being one of the cheapest. Containers sealed with crowns will usually withstand internal pressures of 100 lb./sq. in. Proof of the recog-

BOTTLE CLOSURES 369 nised sealing efficiency of crowned containers is that they are regularly used for export bottling. A particular feature of the international use of crowns is that the dimen- sions of crowns used in North America and Great Britain are within the same dimensional tolerances, as also are those used in most other countries: these dimensional tolerances, in particular overall height and width, being within 0'010 in. This may appear incredible considering the vast numbers used, but even more so is the fact that individual manufacturers aim at tolerances of 0'005 in." This dimensional accuracy of crowns is made not only to ensure good sealing performance a further important reason is to encourage faultless running in high-speed bottling machines, where even minor hold-ups can be costly in regard to output lost, and also with beer bottling, where stoppages can result in faulty material being bottled. Decoration is in the form of coloured coating, or printing and varnishing in all instances a sanitary lacquer is used on the inside of crowns. Liners used are natural or composition cork discs of such thickness that there are 9 to 11 per inch in most instances these are glued in, but in some Continental and South American countries are friction fitted. Some crowns are assembled with vinylire, aluminium or ceresine spots. In general, when used, aluminium spotted crowns are used for beer bottling, vinylire and ceresine for soft drink bottling. Of great importance with the use of crowns is the accurate dimensions of closure finish and the efficient performance of crowning machine. There are two recognised standard crown glass bottle finishes, one for U.S. and one for Great Britain, although some English bottlers use U.S. finish glass bottles. The main advantages and disadvantages of crown closures are as follows: 1. When efficiently used on a good container they can travel with safety under normal conditions to any destination. 2. A crowned container withholds considerable internal pressure without venting. 3. With crown closures the highest bottling speeds can be achieved. 4. When removed from a container, a crown cannot be efficiently re-used. 5. An instrument is always needed for the convenient removal of crowns from containers. MOULDED CAPS The bulk of moulded caps are made from thermosetting moulding powders a few are made from thermoplastic materials, but these are very much in the minority at present. Moulding powders usually used are phenol formaldehyde wood filled,