Uranium
A metal found in a few minerals, as pitchblende, which is an oxide, and uranite, which is a phosphate. The former is its principal ore. The metal, according to the process by which it is obtained, is either in fused white malleable globules or in a black powder. It is used for imparting a yellow tint to glass. See METALS.
Vacuum denotes a space empty or devoid of all matter. When air is removed from a vessel with an air-pump a vacuum is said to be produced. Sometimes a vacuum occurs from natural causes, but it is only for an instant, as the surrounding air rushes in to fill them. The most perfect vacuum until recently was the space above the mercury in a barometric tube. See TEMPERATURE.