PROTECTIVE LACQUER SYSTEMS FOR ALUMINIUM CONTAINERS 11 filling the container with an electrolyte, usually acidified copper sulphate, inserting an electrode and passing a small voltage D.C. current through the cell thus formed. The current or voltage is then noted as are any areas on the container on which metallic copper has been plated out. The second method is based on the same principle, i.e., the resistance of a lacquered surface is inversely proportional to its porosity, and consists of filling the container with a 2% solution of sodium chloride, inserting an electrode and measuring the ratio of the resistances encountered, by a current passing through the test container and an unlacquered container. A 2 volt 800 c.p.s. current is used to obviate polarization effects which may give fallacious results. Rapid information may be gained regarding the film penetrative effects of a product by using a galvanic cell of the Denison type, in which a cutting from a standard lacquered container is made the anode, and a noble metal the cathode, with the actual product the electrolyte. The cell is then coupled to a recording micro-ammeter and a current/time curve obtained which is characteristic of the product under examination in relation to the lacquered anode. When using any method of inspection based on electro-chemical measure- ments, it is essential to first establish correlation with shelf life trials, as the observations obtained by these methods are quite meaningless in themselves. In investigational work it is sometimes necessary to examine a detached lacquer film, and this can best be achieved by filling the container with molten wax or a hot melt vinyl compound, cooling and then dissolving the aluminium in hydrochloric acid or caustic soda. A replica of the container is thus obtained with the complete lacquer film exposed on the outside which may be examined in detail if care is taken in handling it. In conclusion, it is hoped that this paper, which has attempted only to state the present general position and draw attention to defects and some causes of failure, indicates that sufficient is known to make advances in the field of protective lacquering systems so that suitable containers will be available whenever required. (Received: 17th May 1961) GENERAL REFERENCES Bailey, K.C. The Elder Pliny's chapters on chemical subjects 61-101 (1932). (Edward Arnold, London.) Denison, I.A. Corrosion Handbook. 1038. E.P.A. Technical Digest No. 17. Luff, G. & Frederighi, T. Alurninio, No. 4. 391. (July 1954.) Mayne, J. E.O. Corrosion 5, (1952). (Butterworths Scientific Publications, London.) Uhlig, H.H. Corrosion Handbook (1948). (Chapman & Hall, London.)

12 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS •)ISCUSSiON MR. A. HERZKA: (1) What do you consider a sufficient number for shelf tests ? (2) What is your real opinion of vinyl lacquers ? When describing types of lacquers available, you refer to vinyls as excellent, yet when dis- cussing drawbacks you state that "spray coating in the case of vinyls leaves much to be desired". THE LECTURER: (1) One gross tubes, two dozen aerosols. ' (2) Vinyl lacquers are very good, particularly with light applications. The point made in my paper was that it does not matter how good the lacquer is, if it has not been put on in a proper manner it is of no use. The solids content achievable is lower with vinyl lacquers. DR. H. W. HIBBOTT: In reading your paper I felt that in view of all the difficulties of vertical scratching and transverse scratching of flexible containers, no metal tubes get out of the manufacturer's premises at all! Could you let us have more detail of the methods used to inspect and examine vertical and transverse scratching in subsequent screening opera- tions. It does seem that every aluminium tube is suffering from scratches in one direction or another. THE LECTURER ' A lot depends on the product, whether tube or aerosol can. It is extremely important that basic machinery, spindles, and extrud- ing tools are made to a very high engineering standard. Bad tooling and rough edges are to be avoided and a great amount of money and time have to be spent on tool work on the actual machinery itself. This is a matter of precision engineering. DR. H. W. Hm•OTT: On your production plant, when an item is being inspected and a flaw discovered, is it possible that several thousand such items with flaws have passed through your machinery since this item was manufactured, because of the siting of your inspectors and the speed of your machinery ? THE LECTURER: If any defects are found on inspection, the whole of the previous ha!f-hour's production is scrapped. QUESTION: Using the Denison type cell there can be misleading results. In an aluminium collapsible tube one uses a very small proportion of the tube surface and in the case of a lacquered tube, one normally cuts a speci- men from somewhere in the middle of the tube for the test, but in the case of the finished tube, shoulder and nozzle portions are not so well lacquered as the middle, and in addition the bottom of the tube cotfid be damaged in the folding operation. Is not the complete tube necessary and more useful for evaluating products than the straightforward Denison type cell ?