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

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), where A and B are 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 coefficient D in air at 76 cm. varies from 0.0341 to 0.0473 for a temperature variation 15 to 40° C, D being proportional to T3. The diffusion coefficient in H 2 at 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 to T~$. 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.