•    A long clean thick tube closed at one end is filled with pure mercury.

•    The tube diameter is such that capillary effects are minimum.

•    The tube is inserted in the container having mercury. The stopper end is kept well beneath the mercury surface.

•    When the stopper is removed the mercury comes about of the tube into the container and mercury comes out of the tube is falls down by height ‘h above mercury level into the container.

•    Pressure act on mercury are the atmospheric pressure Pat acting on the Hg surface in the container, and mercury vapor pressure Pvp exist at the top of the mercury column in the tube.

From hydrostatic equation

P_at - P_vp = γh


•    Mercury has a low vapour pressure (017 N/m² at 20⁰C) and thus for all intents and purpose it is neglected, where as atmospheric pressure of Hg is 105N/m² at mean sea level.

P_at = γh

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