The Vapor Pressure and Rate of Evaporation of Barium Oxide

Abstract

The extensive investigations of the rate of evaporation of barium oxide by Claassen and Veenemans, and Herrmann are in serious disagreement. In both sets of experiments the oxide was allowed to evaporate from an exposed surface into a vacuum, a method which in this particular case may involve large temperature uncertainties. In the hope of reducing these uncertainties, the method of Knudsen has been applied; in this method the oxide escapes through a small aperture in the wall of a ``blackbody'' at a rate so small that the equilibrium vapor pressure is not sensibly disturbed. The final results are in agreement with those of Claassen and Veenemans. The vapor pressure of barium oxide is given by log 10 p( mm Hg )=8.63–19,400/T(1200–1800 ∘ K ).