JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS distortion. The system is not very good with aluminium because the metal is hard enough to resist everything but the slightest deformation at this edge, and so does not fully compensate for any eccentricity which is often present in the system. (2) The Patented Inner Ring-type Caps. In order that these can function properly the end of the nozzle has to be specially faced off. In one case, an annular ring formed in the top of the cap, adjacent to the threads, has a narrow, flat face leading to a central recess whose vertical walls taper out- wards in the direction of the threads. The tube is extruded to have the normal nozzle, which is subsequently threaded, plus a central extension of smaller diameter which tapers towards its tip. This tapered elongation enters the central recess in the cap and a seal is formed between the two tapers. One can really regard it as a refined version of the plug cap in reverse. A further variation on this theme combines both the inner and outer seal principles. The nozzle end is formed similar to the one just described, whilst the cap has an additional feature in the form of a hollow, central plug. The tapered elongation at the end of the threaded nozzle is forced into the V-shaped annular recess so formed in the cap and a double seal results. In yet another case, the moulded cap is a normal one except for the fact that it has a narrow concentric ring in the form of a V-shaped knife edge where the wad would normally be. The tube nozzle is also normal, but has to be carefully faced off to give a smooth, flat, end surface. When the cap is screwed on, the knife edge bites into the surface of the aluminium to a depth of about 0.003 in., forming a perfect seating. The system is one of extreme simplicity, independent of any location requirements, and takes the principle of applying the available force over the smallest area of contact to its logical conclusion. (3) Wadded Caps. In the majority of cases in which seepage occurs where the ordinary wadded cap is in use, the trouble is due to disintegration of the wad. Shaving creams are particularly bad offenders in this direction. All manner of facing materials have been tried, but the weakness really lies in the compo-cork base. The cap applies pressure between it and a fairly large area of nozzle end surface. Under the effects of prolonged pressure and chemical attack the cork loses its resiliency and eventually seepage must result. The advent of polythene as a liner material was hailed as the answer to this problem of chemical disintegration, but its natural hardness would not permit sufficient compression to ensure that a complete seal was formed. Had human fingers been replaced by a spanner the defect might have disappeared. Only quite recently has the basic principle of applying the available limited force over a minimum area of contact been. called into service. Now we have a heavily chamfered nozzle end whose I16

THE COLLAPSIBLE TUBE sharp edge bites into the polythene wad quite easily and gives an excellent seal. Nothing could be more simple. The compo-cork, or paper-pulp wad faced with metal foil, Ceresin waxed paper, Vinylite coated paper, etc., will continue to be used for the easy jobs, no doubt, but it must have had its day in other cases. Thus, I think it is fair to say that you should no longer suffer seepage at the nozzle. The crimped end presents a very different problem and I wish it were possible to say that there was even one method of effecting 100 per cent security, but, alas, this is not so. The one method which is giving a fair degree of success in certain applications involves the internal waxing of each tube to a depth of about « in. so that the crimp becomes wax filled and thus presents a barrier to liquids of low surface tension. Obviously, this system has little additional physical strength and its performance in hot chmates, where the wax approaches melting-point and the heat produces a rise in internal pressure, must be carefully watched. Thermoplastic coatings, such as vinyl or latex, offer increased physical strength, but are less amenable to migration under crimping pressure-- even when the jaws are hot--and thus often fail to fill that a•vkward tunnel which forms along the edges of the fold. This can only be counteracted by the use of a fairly heavy coating which, in its turn, causes production difficulties to the tube maker, although these are in the process of being overcome. The use of external clips, dipping of the crimped tube end into sealing compounds after filling, and such-like procedures are generally unsightly, troublesome, and often quite ineffective. Pressure welding was tried on tin tubes years ago, but with very limited success. In the first instance, with the optimum conditions of pressure supplemented by heat, a considerable reduction in metal thickness (50-70 per cent) is essential before a satisfactory weld ensues. When working with a tube wall only 0-005 in. thick one can hardly afford this if reasonable strength is to remain. Secondly, any trace of product between the surfaces to be joined leads to inevitable failure. Electric arc and ordinary flame welding have also been tried with varying degrees of success. You may well say that this is a rather sorry story to tell, haven't you got any ideas for solving it in the future ? We have one idea which is being investigated and, strangely enough, it concerns the aluminium tube which one might expect to be the most difficult. It is hoped to extend the use of collapsible tubes in the food industry and in many cases an hermetically sealed container, able to withstand sterilisation, is essential. Hence, we must solve it. Don't think that the answer is just around the comer or ask me to forecast how soon it will be available. If I can give you nothing more positive, at least I offer you some encouragement to go on hoping. 117