Caesium iodide, CsI

The Caesium iodide, CsI, is prepared by the action of caesium sulphate on barium iodide. It forms crystals, melting at 621.0° C., and boiling at 1280° C., the vapour-pressure in atmospheres corresponding with the expression

log p = -36600/4.57T+5.165.

The density is given as 4.523, 4.508 at 22.8° C., and 4.510 at 25° C. At 35.6° C. its solubility is 106 grams in 100 grams of water. Its heat of solution is -8.25 Cal. A tri-iodide and a pentaiodide have been isolated, and the existence of a heptaiodide and of an enneaiodide, CsI₉, is probable.