1. A heavy silvery-white metallic element, radioactive and toxic, easily oxidized, and having 14 known isotopes of which U 238 is the most abundant in nature. the element occurs in several minerals, including uraninite and carnotite, from which it is extracted and processed for use in research, nuclear fuels, and nuclear weapons. atomic number 92; atomic weight 238.03; melting point 1,132°C; boiling point 3,818°C; specific gravity 18.95; valence 2, 3, 4, 5, 6. see table at element.

1. the element with atomic number 92 and symbol U.

1. an element of the chromium group, found in certain rare minerals, as pitchblende, uranite, etc., and reduced as a heavy, hard, nickel-white metal which is quite permanent. its yellow oxide is used to impart to glass a delicate greenish-yellow tint which is accompanied by a strong fluorescence, and its black oxide is used as a pigment in porcelain painting. symbol U. atomic weight 239.

1. metallic uranium, as obtained in the fused condition by means of an electric furnace, is compact, white, and lustrous, capable of taking a high polish, of sp. gr. 18.7, melting at a very high temperature, and volatilizing more readily than iron, slowly acted upon by water at ordinary temperature, burning in oxygen or chlorin, and combining freely with nitrogen at 1000° C. the foundation was laid for the modern study of the phenomena of radioactivity when, in 1896, M. henri becquerel observed that a salt of uranium emits rays which affect a photographic plate screened by black paper opaque to ordinary light. this property proved to be common to all the salts of uranium and to uranium itself, and is exhibited continuously by uranium and its compounds even when they are kept in darkness. the intensity of the radiation is not materially affected by change of temperature within very wide limits. not only are photographic effects produced by the radiation from uranium compounds, but positively or negatively electrified bodies, also, are discharged by ionization of the surrounding air. subsequent investigation has shown that the uranium radiation is complex, and includes the emission of rays of the three types which have been designated as
2. chemical symbol, U; atomic weight, 240. A metal discovered by Klaproth, in 1789, in a mineral which had been long known, and called pitch-blende, but which was supposed to be an ore of either zinc or iron.

1. a heavy toxic silvery-white radioactive metallic element; occurs in many isotopes; used for nuclear fuels and nuclear weapons