Caesium peroxides

Three peroxides have been prepared by heating the metal in aluminium vessels with the calculated proportions of oxygen, or by the action of oxygen on a solution of the metal in liquid ammonia at -50° to -70° C. Caesium dioxide, Cs₂O₂, forms yellowish, acicular crystals, which become brown with rise of temperature, and at 400° to 450° C, melt to a black liquid. At 650° C. it begins to decompose with evolution of oxygen. It has a density of 4.47 at 15° C. It dissolves slowly in slightly acidulated water, forming hydrogen peroxide. The heat of formation from its elements is 107.0 Cal. Caesium trioxide, Cs₂O₃, is a black substance, melting at 400° C., the density at 0° C. being 4.25. With water it evolves oxygen, forming hydrogen peroxide. The heat of formation of the trioxide from its elements is 127.46 Cal. Caesium tetroxide, Cs₂O₄, is formed by oxidizing the metal between 300° and 350° C. It is a golden-yellow, crystalline powder, melting in an oxygen atmosphere at 518° C., the density at 0° C. being 3.68, and at 19° C. 3.77. It darkens with rise of temperature, and decomposes readily. With moisture it deliquesces and reacts in accordance with the equation

Cs₂O₄+2H₂O = 2CsOH+H₂O₂+O₂.

Heating with carbon dioxide forms the caesium carbonate and ozone:

Cs₂O₄+CO₂=Cs₂CO₃+O₃.

It is reduced by hydrogen. The heat of formation from the elements is 141.46 Cal.