1904, Institution of Mining and Metallurgy (Great Britain), Bulletin, Institution of Mining and Metallurgy (Great Britain) (1904), p. 22,"In mining work difficult laying conditions, limited space, and movements of the ground, all combine to make the installation of a leakproof main with ordinary joints a very difficult matter."
1967, Edward Locker Delmar-Morgan, Maintenance of Inboard Engines, Newnes (1967), p. 115,"There are two subdivisions in the flashlight dry cell range, the ordinary cheap one and the better-quality leakproof cell."