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Physical Properties of Uranium

Pure uranium is a lustrous white metal. When prepared by electrolysis of uranous chloride it is deposited as small glistening crystals; 7 by reduction of the oxide it is usually obtained as a brown or black powder. The metal is malleable, but less so than thorium; it is very ductile and is capable of taking a high polish. It is not hard enough to scratch glass. Its density at 13° C. is 18.685. The metal, when free from iron, is slightly paramagnetic, the susceptibility being +0.9×10-6.

The position of the metal in the electromotive series is not conclusively determined. The electrical potential of uranium in contact with aqueous electrolyte has been measured by Muthmann and Fraunberger, who showed that the pure metal, in contact with a normal solution of potassium chloride, in the element


assumed a potential Hh = -0.46. The metal showed no tendency to become passive, nor does it in the usual passivating anodic solutions, though the latter may be in considerable concentration and a high current density applied. Using an electrode of platinum on which finely powdered uranium was pasted by means of gelatin, Pierle obtained the following value for the metal in contact with an aqueous solution of uranyl nitrate:

U(91.49 per cent.)/UO2(NO3)2 = -0.093 volt.

By placing the metal in contact with an alcoholic solution of uranium hexachloride, Fischer and Rideal obtained values which placed the potential of uranium between those of copper and hydrogen. This, however, is not in agreement with the above results.

The specific heat and atomic heat of the element have been determined as follows:

Temperature, ° C.Specific Heat.Atomic Heat.
0 to 980.02806.66

Uranium melts at a white heat, but the exact temperature has not been determined; Guertler and Pirani found it to be about 1850° C., which is in agreement with a statement by Moissan that uranium is more difficult to melt than platinum. Rideal melted in a vacuum a specimen of uranium containing 0.4 per cent, carbon; fusion occurred between 1300° and 1400° C. The boiling-point has not been determined, but Moissan found that the metal could be distilled more readily than iron in the electric furnace.

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