Category:Vacuum

Vac"u*um, n.; pl. E. Vacuums, l. Vacua. Etym: [l., fr. vacuus empty. See vacuous.]

1. (physics)

Defn: 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.