Designed for demonstration, the column is clearly visible to the whole class without them having to crowd around the demonstration bench. A widebore glass tube is mounted vertically in front of a scale graduated 0 to 60cm. Zero corresponds to the inside of the closed (top) end of the tube.  Air is confined in the tube by a coloured oilcontained in a metal pressure chamber which is fitted with a Bourdon-type gauge. As the pressure in the oil chamber is increased oil is forced into the glass tube and the volume of the contained air and its actual (total) pressure are directly indicated. The oil chamber can be filled with oil by just removing the screw valve fitted on the chamber and two valves in side of chamber one to generate pressure and another to release the pressure from chamber.