Barium Hydride, BaH₂

Barium Hydride, BaH₂, was first obtained by the action of magnesium on barium oxide at red heat in an atmosphere of hydrogen. An impure product, to which Winkler ascribed the formula BaH, was formed, but Guntz showed that it was probably a mixture of equivalent quantities of the hydride BaH₂ and barium oxide. It may be prepared by the action of hydrogen on barium amalgam at a high temperature. Hydrogen is absorbed by finely powdered barium even at 120° C., and at 170°-180° C. the reaction is vigorous. Absorption by a cadmium- barium alloy begins at 350° C.

The pure compound is crystalline, practically white, and of density 4.21. At 1400° C. it is slowly volatilised in a current of hydrogen. The heat of formation is 37.5 Cal. The temperature of fusion is in the neighbourhood of 1000° C. It is readily attacked by water and moist air, forming barium hydroxide, and by nitrogen above red heat. Molten barium hydride absorbs nitrogen.

Barium hydride is the least stable of the three alkaline earth hydrides, and the difficulties encountered in studying the vapour pressures of calcium and strontium hydrides are increased in this case by the volatility of barium hydride.