Uranium Trichloride, UCl₃

Uranium Trichloride, UCl₃, may be obtained by heating uranous chloride in hydrogen. It is a reddish-brown substance which readily dissolves in water, yielding a red solution. It may be crystallised in the form of glistening, dark red, hygroscopic needles. The solution is not stable, but gradually turns green with evolution of hydrogen.

The chloride may also be obtained in solution by the reduction of uranyl salts in hydrochloric acid solution, either by means of nascent hydrogen, or by electrolysis in a special apparatus, in which a layer of mercury is used as the cathode, the anode being of carbon, and the whole is cooled in ice. In the latter case, traces of dissolved mercury or platinum are liable to act as negative catalysts and stop the reduction when the uranium is in the tetravalent condition. The solutions of the trichloride obtained contain excess of hydrochloric acid and are purple red; they are comparatively stable, but are readily converted into uranous compounds.