Vac"u*um (?), n.;
pl. E. Vacuums (#), L. Vacua (#). [L., fr.
vacuus empty. See Vacuous.]
1. (Physics) A space entirely devoid of matter (called also, by way of distinction, absolute vacuum); hence, in a more general sense, a space, as the
interior of a closed vessel, which has been exhausted to a high or the highest degree by an air pump or other
artificial means; as, water boils at a
reduced temperature in a vacuum.
2. The condition of rarefaction, or reduction of pressure below that of the atmosphere, in a vessel, as the condenser of a steam engine, which is nearly exhausted of air or steam, etc.; as, a vacuum of 26 inches of mercury, or 13 pounds per square inch.
Vacuum brake, a kind of continuous brake operated
by exhausting the air from
some appliance under each car, and so
causing the pressure of the atmosphere to apply the brakes. -- Vacuum pan (Technol.),
a kind of
large closed metallic retort used in sugar making for boiling down sirup. It is so connected
with an exhausting apparatus that a partial vacuum is formed within. This allows the evaporation and concentration to take place
at a lower atmospheric pressure and hence also at a lower temperature, which largely obviates the danger of
burning the sugar, and shortens the process. -- Vacuum pump. Same as Pulsometer, 1. -- Vacuum tube (Phys.),
a glass tube provided with platinum electrodes and exhausted, for the passage of the electrical discharge;
a Geissler tube. -- Vacuum valve, a safety valve opening inward to admit air to
a vessel in
which the pressure is less than that of the atmosphere, in order to prevent collapse. --
Torricellian vacuum. See under Torricellian.
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