I t seems worthwhile to report on a unique, economical, and effective design of evaporation tanks. Such tanks have been in continuous use for fifteen years at Michelson Laboratory, producing research quality evaporated films. Briefly, each tank consists of a 83.8 cm × 50.8 cm × 1.9 cm vertical stainless steel (316) base plate and a 83.8 cm × 50.8 cm × 2.5 cm vertical Pittsburgh Duplate two-ply laminated glass cover plate (four-ply laminates are unsatisfactory), separated by an 20.3-cm wide stainless steel elliptical hoop having a 76.2-cm major axis and an 45.7-cm minor axis, as shown in Fig. 1. The steel fins welded on the sides provide additional support to the ellipse. The base and cover plate seals are provided by L-shaped neoprene gaskets which are commercially available for 61.0-cm bell jars. When considerable heating of the substrates is required, Viton L-shaped gaskets are substituted for the neoprene gaskets. Figure 2 shows two tanks separated by approximately 71.1 cm to provide the necessary space for a forepump, diffusion pump, valves, and piping to evacuate either tank. A single set of instruments and power supplies is used for both tanks of such a dual arrangement, which provides for additional economies of construction and maintenance. Such a dual arrangement requires a minimum laboratory space of 50.8 cm × 121.9 cm × 152.4 cm and provides for routine evaporations at pressures in the vicinity of 10–10 Torr. The large ratio of base plate area to evacuated volume in the elliptical evaporation tank provides the following advantages over conventional glass bell jars: (1) shorter pumping time, (2) larger source-to-substrate distance, (3) larger internal area for the attachment of measuring and control devices, (4) larger window area for observation during an evaporation, and (5) greater flexibility of internal arrangement of component parts for general experimental work. When a 45.7-cm coating distance is used Fig. 1. Front view of elliptical evaporation tank.