The rate of evaporation of droplets. II. The influence of changes of temperature and of the surrounding gas on the rate of evaporation of drops of di-n-butyl phthalate

Abstract

The vapour pressure of di-n-butyl phthalate has been determined by Knudsen’s method at 15 to 40° C and is given by log'10p(in microns) = — 4790/T+ 14-502. The latent heat of evaporation is 21,910 cal. per mole. Rates of effusion through a small hole in the presence of pressures of air 2 to 0 01 cm. have also been determined and shown to conform to the equation rate of loss of mass =A|(B + P), whereAandBare constants. The rate of evaporation of drops of di-n-butyl phthalate about 0-5 mm. in radius has been determined at 15 to 40° C, in air at pressures 20 to 0-01 cm. and in hydrogen at 19.90° C and Freon 12 (CC12F2) at 19.90 and 30.00° C and has been accounted for theoretically. Within the experimental error the evaporation coefficient is unity at all temperatures. The diffusion coefficientDin air at 76 cm. varies from 0.0341 to 0.0473 for a temperature variation 15 to 40°C, Dbeing proportional toT3. The diffusion coefficient in H2at 19*90° C is 0*153 for 76 cm., and for diffusion in Freon 12 at 76 cm. is 0.0126 at 19.90° C and 0.0140 at 30.00° C. The collision radius of di-n-butyl phthalate is 4.45 A as determined from the experiments in air at 19*90° C and the sum of the radii of di-n-butyl phthalate and air molecules is proportional toT~$. From the experiments in hydrogen the collision radius of di-n-butyl phthalate is 4.68 Å at 19.90° C and from the experiments using Freon 12, 5.24 Å at 19.90° C. The shape of the drops has been studied, and errors introduced by assuming a spherical shape are shown to be negligible.