Pump, Swinburne.
A form of mechanical air pump for exhausting incandescent lamp bulbs.
Referring to the cut, A is a bulb on the upper part of a tube G; above A
are two other bulbs C and D. From the upper end a tube runs to the bulb
E. Through the cock L, and tube F connection is made with a mechanical
air pump. The tube H leads to a drying chamber I, and by the tube J
connects with the lamp bulbs or other objects to be exhausted. The tube
G enters the bottle B through an airtight stopper, through which a
second tube with stopcock K passes. In use a vacuum is produced by the
mechanical pumps, exhausting the lamp bulbs to a half inch and drawing
up the mercury in G. The bent neck in the bulb E, acts with the bulb as
a trap to exclude mercury from F. When the mechanical pumps have
produced a vacuum equal to one half inch of mercury, the cock L is
closed and K is opened, and air at high pressure enters. This forces the
mercury up to the vessel D, half filling it. The high pressure is now
removed and the mercury descends. The valve in D closes it as the
mercury falls to the level G. Further air from the lamps enters A, and
by repetition of the ascent of the mercury, is expelled, through D. The
mercury is again lowered, producing a further exhaustion, and the
process is repeated as often as necessary.
Fig. 278. SWINBURNE'S AIR PUMP.
Push-Button.
A switch for closing a circuit by means of pressure applied to a button.
The button is provided with a spring, so that when pushed in and
released it springs back. Thus the circuit is closed only as long as the
button is pressed. The electric connection may be made by pressing
together two flat springs, each connected to one of the wires, or by the
stem of the button going between two springs, not in contact, forcing
them a little apart to secure good contact, and thereby bridging over
the space between them.