Utilising the abeolute critical temperature (Tc) data for maids of high melting points, as recorded by von Grosse4, it has been shown that the absolute melting points (Tm) of alkali halides and of alkali and some other metals are the corresponding temperatures Tm, Tb (absolute boiling point), and Tc of francium halides and alkali astatides have heed estimated from the known approximate constant ratios: —Uo/Tm—Uo/Te and (— U0 being the lattice energy) for the other members of this family. Further. Tms of XeF2 and XeF4 are estimated to be about 100º and 190°, respectively. and the heat of sublimation of XeF6 to be about 10.4 heal.