The vapor pressure of uranium hexafluoride, has been determined from 0 deg C to 85 deg C in a copper apparatus. The data obtained are given by the two equations log 10 P mm Hg = 2623.3/T + 10.8407 (solid, vapor), log 10 P mm Hg = -1505.9/T + 7.5223 (liquid, vapor) and the latent heats are: delta H sub sub = 12.00 kg-cal, delta H sub vap = 6.89 kg-cal. The experimental arrangement is shown in Figure 1. This consists of a reservoir A in a thermostat and a brass sylphon bellows for the measurement of pressure by a null method. The pressure above an atmosphere was read on a multiple mercury manometer using dibutylphthalate as a piston liquid. p2.