A molecular flow evaporation apparatus for measuring vapour pressures and heats of sublimation of organic compounds

Abstract

The method of free molecular evaporation has been applied in a modified form to enable construction of a simple apparatus for measuring rate of change of vapour pressure with temperature. The design used introduces considerable restriction to free molecular flow and produces low apparent vapour pressures. These can, however, be corrected to yield the proper static values if the evaporation coefficient is known. The apparatus has been tested with anthracene, benzoic acid and naphthalene. Naphthalene has given spurious results because of self-cooling due to rapid sublimation.