Caesium hydride, CsH

It is difficult to prepare the Caesium hydride, CsH, in a state of purity. It can be obtained in the form of white crystals by the interaction of pure caesium and pure hydrogen, its general characteristics being similar to those of the corresponding rubidium derivative. Ephraim and Michel produced it by heating a mixture of caesium carbonate and metallic magnesium in hydrogen at 580° to 620° C. for three days. It is the least stable of the alkali-metal hydrides. Its density is 2.7. Ephraim and Michel found the vapour-tension for each interval of 10° between 340° and 440° C. to be 78, 100, 126, 160, 202, 256, 317, 402, 503, 630, and 787 mm.; but the measurements may have been vitiated by the presence of carbon dioxide arising from decomposition of the magnesium carbonate formed, by the sublimation of the metal, and by its solubility in the hydride.