Rates of evaporation IV. The rate of evaporation and vapour pressure of rhombic sulphur

The rate of evaporation in vacuo and vapour pressure of bipyramidal crystals of rhombic sulphur ({111}) have been determined in the range 15 to 32.5° C; the rate of evaporation of a polycrystalline bead of rhombic sulphur has been determined at 30° C over a range of air pressures. The diffusion coefficient of S8 molecules in air is 0.0884 cm.2 sec.-1 at 30° C; the evaporation coefficient is 0.73 ± 0.05 and appears to be temperature independent over the range studied. The linear velocity of the interface on evaporation is given by 1-91 x 1011T-1/2e-23,890/RT cm. sec. -1. The vapour pressure is given by log10p cm. = -5240/T + 10.763. The temperature independent factor for the rate of evaporation and the Value of the evaporation coefficient are discussed in terms of statistical mechanics.