A form of mercurial air pump. It is used for exhausting Geissler tubes,
incandescent lamp bulbs and similar purposes.

Referring to the cut, A is a reservoir of mercury with flexible tube C
connected to a tube at its bottom, and raised and lowered by a windlass
b, the cord from which passes over a pulley a. When raised the mercury
tends to enter the chamber B, through the tube T. An arrangement of
stopcocks surmounts this chamber, which arrangement is shown on a larger
scale in the three figures X, Y and Z. To fill the bulb B, the cocks are
set in the position Z; n is a two way cock and while it permits the
escape of air below, it cuts off the tube, rising vertically from it.
This tube, d in the full figure connects with a vessel o, pressure gauge
p, and tube c, the latter connecting with the object to be exhausted.
The bulb B being filled, the cock m is closed, giving the position Y and
the vessel A is lowered until it is over 30 inches below B.

This establishes a Torricellian vacuum in B. The cock n is now turned,
giving the position X, when air is at once exhausted from the vessel
connected to C. This process is repeated until full exhaustion is
obtained. In practice the first exhaustion is often effected by a
mechanical pump. By closing the cock on the outlet tube c but little air
need ever find its way to the chambers o and B.