Concerning operator differences, it was noticed that an improvement in ß :i•'. precision occurred over the initial period of seven days or so, but then a slow .: deterioration occurred. The error variance in the units used above fell from .' 50 to about 20 (the value of 7.7 for operator Z was never found again) and then rose to 30-40 after the operator had been engaged on the work for a :::' :': month or so. The acquiring of a reproducible and rhythmic washing tech- nique followed by a decline in care and attention as interest waned would account for these results. The higher the repeatability that obtains the fewer the tests that need to be performed, and if the operators can be led to appreciate this point then reasonably high precision ought to be maintainable. REFERENCES • Clifford Pugh, Applied Statistics, 2, 172 {1053). • A. W. Middleton, •[.S.C.C., III, 253 (1052). a D. S. McArthur, E. L. Baldeschweiler, W, H. White, J. S. Anderson, Anal. Chern., ß ::::2•: 26, 1012 (June, 1954). 4 K. A. Brownlee, "Industrial Experimentation," H.M.S.O., 1949 (a) pages 38-9, ': (b) pages 111-114. A Lecture delivered to the Society on 22nd October, 1954

THE COLLAPSIBLE TUBE G. E. HOLMES, M.A., A.R,I.C.* The physical properties and corrosion resistance o• those metals suitable for the manufacture of tubes are surveyed, and methods of inhibition of corrosion ant1 of reduction of seepage summarised. TIlE METAL collapsible tube finds so many applications in present-day life that there can be very few homes in this country which do not contain at least one in current use. Such a wide distribution, coupled with the fact that it is an expendable product, has produced a thriving industry able to turn out a mass-produced article, of exceedingly high quality, at a relatively low cost. According to reliable estimates, some 300 million tubes are used in Britain per year, a truly staggering total. You will notice that I said "tubes," not collapsible tubes, for that abbreviated form of the name is universally accepted in spite of the fact that it should strictly be used only in connection with piping. Familiarity readily overrides such matters of detail. I hope you will forgive me if I preface my talk on the collapsible tube with a few words about the body which has organised this, and a number of other lectures which are being given in various parts of the country during this autumn. The Collapsible Tube Manufacturers Association (or C.T.M.A. *The Collapsible Tube Manufacturers Association, 47, \¾elbeck Street, London, W. 1. 107