Calcium Subfluoride, CaF or Ca₂F₂

Guntz and Bassett attempted to prepare a subchloride, subiodide, and Calcium Subfluoride, CaF or Ca₂F₂, by heating together mixtures of metallic calcium with the chloride, iodide, and fluoride respectively, under varying conditions. They came to the conclusion, however, that the so-called subhalides were merely mixtures of unaltered salt with a little hydride and oxide, resulting from the accidental presence of small quantities of water. Hence the property of liberating hydrogen from water, shown by these products, was due to the action of hydride on water.

Wohler and Rodewald, on the other hand, stated that by heating together calcium and calcium fluoride above 1400° C. in a steel tube, protected by wrapping in platinum foil and coating with basic fireclay, crystals were obtained of a red to orange-yellow colour with a metallic lustre, and of composition corresponding to the formula CaF. Formation only began above 1100° C. Below this temperature the compound split up into metallic calcium and the fluoride. To obtain the subfluoride stable at the ordinary temperature, it had to be cooled rapidly by quenching in solid carbon dioxide. By treatment with bromoform the subfluoride could be separated from the fluoride owing to difference of density. The subfluoride is not so deliquescent as the subchloride and subiodide, and is less easily attacked. The density at 20° C. is 2.305.