THE CONSTRUCTION, TESTING AND USE OF A NEW KNUDSEN EFFUSION APPARATUS

The construction of a new Knudsen effusion apparatus for measuring vapour pressures of organic and organometallic solids as a function of temperature and the subsequent calculation of enthalpies of sublimation are described. The new apparatus enables the simultaneous operation of three different effusion cells, reducing, considerably, the time necessary for the study of each compound. The performance of the apparatus was checked by measuring, as a function of temperature, the vapour pressure of benzoic acid (between 307.15 and 314.15 K) and ferrocene (between 292.27 and 300.01 K), from which their standard molar enthalpies of sublimation, at 298.15 K, were derived: benzoic acid, ΔcrgH298.15XXX = 89.25±0.85 kJ mol-1; ferrocene, ΔcrgH298.15XXX = 72.39 ± 1.00 kJ mol-1. © 1990.