Uranium

Uranium (sym. U, equiv. 240) is a very hard but moderately malleable metal, sp. gr. 18.33, resembling nickel or iron in its lustre and colour; but in a finely comminuted state occurring as a black powder. It is not oxidised by exposure to air or water at ordinary temperatures; but if heated in the air it burns brilliantly, and is converted into oxide. It is a comparatively rare metal, which never occurs native; its chief source being Pitch-blende, which contains from 40 to 90 per cent. of black oxide. Uranium forms at least four oxides—viz. two principal ones—a dioxide, $UO\_2$, and a uranic oxide, $UO\_3$; and two intermediate oxides—the black oxide, $UO\_2\; +\; UO\_3$, and the green oxide, $UO\_2\; +\; 2UO\_3$. The black oxide is of much value as a pigment for colouring porcelain; and compounds of uranic oxide with the earths are employed to communicate a peculiar yellow tint to glass. The salts of the dioxide have a green, and those of the trioxide a yellow colour. Uranium with platinum and copper forms two beautiful alloys resembling gold in appearance. The metal is extracted from pitch-blende; and its isolation in a pure form is due to Peligot in 1842. The metal was not obtained in the compact form till 1856; it is found in Saxony, Bohemia, and Cornwall, usually in patches; in 1889 a lode was found in Cornwall. The price reaches £2400 a ton. For uranium in the electric furnace, see Nature, vol. liv.