URANIUM (U), a metal discovered by Klaproth, in 1789, who named it after the planet Uranus, the discovery of which had occurred in 1781: the mineral from which it was first obtained is called peekblenck, which contains about 80 per cent. of the black oxide of uranium This and other minerals from which uranium is extracted are described in the NATURAL HISTORY DIVISION of this Cyclopedia.
31. Peligot obtains this metal by decomposing its chloride by means of potassium or sodium, a process which has been successfully adopted for procuring aluminum and magnesium : the metal ao separated is partly in the state .of a black powder. and partly agglomerated; by carefully detaching the portions which adhere to the sides of the crucible, plates of a metallic lustre comparable to that of silver, are obtained ; these are susceptible of being filed, but possess a certain degree of malleability, and have evidently undergone incipient fusion. Uranium is very combustible ; at a moderate degree of beat, in contact with the air, it burns with a remarkably white and shining light ; the combustion occurs at so low a temperature, that it may take place on paper without causing it to burn. If small particles be shaken from the filter on which the metal iu powder has been collected, portions so minute as to be scarcely visible burn with brilliant spark's on corning near the flame of a candle. When heated in a capsule, uranium burns brilliantly, and is converted into a deep grecn-coloured oxide, the bulk of which is considerably greater than that of the metal employed.
Uranium does not appear to suffer any alteration by exposure to the air, nor does it decompose water at common temperatures, but when put into diluted acids it dissolves in them with the evolution of hydrogen gas. It somewhat resembles iron and manganese in its chemical character. Its cqnivalent number is 00.
Having now described the properties of uranium we proceed to con sider the compounds which it forms with other bodies.
Oxygen and to 31. Paget, there exist., or may be formed, three oxides of uranium : the protoxide, formerly con sidered as metallic uranium ; that prepared by calcining the nitrate, known by the name of deutoxido of uranium, or uranous acid; lastly, the peroxide, uranic acid, which enters into the composition of the yellow salts. Besides these oxides, it is stated, by the chemist above
named, that there are two suboxides of uranium produced by the decomposition of the aubehloride by ammonia, and an oxide inter mediate between protoxide and peroxide of uranium, which is formed when the oxide obtained by calcining the nitrate is submitted to the action of oxygen.
Suboxide of Uranium When ammonia is added to a solution of subehloride of uranium a brown precipitate is formed, which undergoes various changes of colour and composition by absorbing oxygen. Its extreme instability renders its analysis very difficult. It decomposes water, to combine with its oxygen to form the apple-green enboxido, the analysis of which is equally difficult.
Pro oxide of Uranium (U 0), formerly regarded na metallic uranium. This may be prepared by several processes; one of the best consists in decomposing the yellow oxalate of uranium by hydrogen : the process requires several precautions. Prepared in this manner the protoxide is extreme pyrophorie, the access of air causing it to burn with feeble incandescence and converting it into black peroxide : it is of a cinnamon brown colour. When the .protoxide of uranium is obtained by reducing the double chloride of potassium and uranium, not by means of hydrogen, it is obtained in crystalline scales isoseessing a high degree of lustre, and being then in a higher state of aggregation it is not pyrophorie ; and when procured by decomposing the nitrate, the protoxide is of a maroon colour. When thus prepared in the dry way, it is not acted upon either by hydrochloric or sulphuric acid when diluted ; but dissolves in the latter, when concentrated : nitric acid also dissolves it, but nitrate of peroxide of uranium is obtained.