Radium Barium Platinocyanide, BaRa₂[Pt(CN)₄]₂

Since the majority of platinocyanides fluoresce under the influence of radiations from radioactive substances, the radium salt should be self-luminous. The radium barium salt was prepared 1 by dissolving radioactive barium chloride in water and boiling the solution with excess of silver platinocyanide. After filtering off insoluble silver salts the solution was allowed to crystallise in a desiccator.

The crystals deposited last were reddish in colour, and brightly luminous at first, but the intensity of their luminosity gradually diminished, and the reddish tint deepened in colour. No doubt this is attributable to alteration of the barium platinocyanide in the complex, since the free salt upon exposure to radium radiations undergoes some change, resulting in a weakening of the fluorescence as has already been pointed out.

The radium barium salt recovers its fluorescent properties upon recrystallisation, and the effect is enhanced by contact with its own saturated aqueous solution, probably because the water prevents the alteration referred to.