The sublimation of ZrI4 was studied by a torsion effusion-gravimetric technique in which the molecular weight of the effusing gas and its pressure in the effusion cell were measured simultaneously. The sublimation pressures of ZrI4 were found to depend on the orifice size of the effusion cell. The measured pressures were extrapolated to zero orifice size to obtain the equilibrium vapor pressures, which could be represented by the equation
-+-86log P(ZrI4, atm) ----9.79 • 0.19 --.(from 410 ~ to 480~ T Enthalpies above room temperature, up to 703.1~ for solid zirconium tetraiodide were measured in a copper-block, drop calorimeter. The enthalpy increments above 298.15~ were expressed by the equation HT ~ --H29s ~ (kcal/mole) = 29.