The tank is designed for impregnating with polyvinyl acetate (Gelva V-7) in methylated spirits (or 95% ethyl alcohol). It consists of a 24-inch diameter, 30-inch high cylindrical container of Ï-inch steel plate. In the circular lid, which can be clamped down, are two 4-inch diameter holes for an observation window and illumination by an external lamp. Pressure is controlled through a needle valve, also mounted in the lid. Vacuum is provided by a Metrovac Vacuum Pump G.D. R.1. This never exceeds 60 mm Hg, which is the pressure at which alcohol boils at normal temperature. For impregnation, objects are placed in a wire-mesh tray and lowered into the solution of polyvinyl acetate. The pump is operated until all bubbling subsides, the valve is opened, the lid lifted, and the objects withdrawn and allowed to drain. Cost of apparatus was pound sterling172. Cost of one charge of polyvinyl acetate solmion is pound sterling24.