URANIUM, in chemistry, a metal dis covered by Klaproth in the year 1789. It was then announced as a metal more dif ficult to be reduced than manganese, ex ternally of a grey colour, and internally of a clear brown, of considerable lustre, and middling hardness, that it might be scratched And filed, and that its oxide gives a deep orange colour to porcelain. It has been obtained from three different minerals. The first is in the state of sulphuret, of a blackish colour, and of a shining fracture, and sometimes lamel lated. In this state it is sometimes com bined with iron and sulphurated lead. The uranium is in the metallic state.
The second ore from which this metal is obtained, is the native oxide of ura nium. It is always in the state of yellow powder, on the surface of the sulphuret. The specific gravity is 3.24. When it is of a pure yellow colour it is then a pure oxide.
The third ore of the metal is the native carbonate of uranium. Of this there are two distinct varieties, the one of a pale green, and sometimes of a silvery white colour. This contains but a small quan tity of the oxide of copper, and is very rare. The other is of a shining deep green, which is the green mica, or glim mer, of mineralogists. Klaproth suppos. ed that it contained an oxide of uranium, mixed with the oxide of copper ; but it has been since discovered to have carbon ic acid in its composition. It is crystal lized in small square plates, and some times, though rarely, in complete octahe drons.
The process by which Klaproth reduc ed this metal is the following : he mixed the yellow oxide of uranium, precipitated from its solutions by an alkali, with lin seed oil, in the form of a paste, and this being exposed to a strong heat, there re mained a black powder, which had lost rather more than one-fourth of its weight.
It was then exposed to the heat of a por celain furnace, in a close crucible, and the oxide was afterwards found in a coherent mass, but friable under the fingers, and reduced to a black shining powder. It decomposed nitric acid with effervescence. This black powder, covered with calcin ed borax, was for the second time exposed to a still stronger heat, by which me. tallic mass was obtained, consisting of ve ry small globules adhering together.
The colour of uranium is of a dark grey, and internally of a pale brown. It haS little brilliancy, on account of the spongy mass, in which state it is obtained. It may be scratched with a knife, and is extremely infusible. The specific gravi ty is 64. When uranium is exposed to a red heat in the open air, or when it is acted on by the blow-pipe, it undergoes no change. 'File yellow oxide of uranium does not melt. It acquires a brownish. grey colour when it is long heated in the air, but it has not been ascertained whe ther it gains or loses oxygen. The oxide of uranium is reduced by means of char coal, when it is exposed to heat. The yellow oxide, when mixed with common enamelling dux, tinges porcelain of a deep orange colour.