Abstract: wt% ThO/sub 2/ at 2450 deg K. The vapor pressure equation for ThO/sub 2/(s) was also determined by the effusion method in a tungsten cell over the temperature range of from 2268 to 2593 deg K. The vapor pressure equation for ThO/sub 2/(s) -- ThO/sub 2/(g) is: log P (atm) = ization data for solid thorium gave the following equation for Th(l) -- Th(g): log P (atm) = --27,960/T + 5.575. However, solubility studies indicated that the partial pressures of Th and ThO2 from a mixture of Th(l) and ThO/sub 2/(s) would be less than that obtained from the pressure equations for Th(g) and ThO/sub 2/(g). (auth)