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 degrees C and is given by log$_{10}$ p (in microns) = - 4790/T + 14$\cdot $502. The latent heat of evaporation is 21,910 cal. per mole. Rates of effusion through a small hole in the presence of pressures of air 2 to 0$\cdot $01 cm. have also been determined and shown to conform to the equation rate of loss of mass = A/(B+P), where A and B are constants. The rate of evaporation of drops of di-n-butyl phthalate about 0$\cdot $5 mm. in radius has been determined at 15 to 40 degrees C, in air at pressures 20 to 0$\cdot $01 cm. and in hydrogen at 19$\cdot $90 degrees C and Freon 12 (CCl$_{2}$F$_{2}$) at 19$\cdot $90 and 30$\cdot $00 degrees C and has been accounted for theoretically. Within the experimental error the evaporation coefficient is unity at all temperatures. The diffusion coefficient D in air at 76 cm. varies from 0$\cdot $0341 to 0$\cdot $0473 for a temperature variation 15 to 40 degrees C, D being proportional to T$^{3}$. The diffusion coefficient in H$_{2}$ at 19$\cdot $90 degrees C is 0$\cdot $153 for 76 cm., and for diffusion in Freon 12 at 76 cm. is 0$\cdot $0126 at 19$\cdot $90 degrees C and 0$\cdot $0140 at 30$\cdot $00 degrees C. The collision radius of di-n-butyl phthalate is 4$\cdot $45 angstrom as determined from the experiments in air at 19$\cdot $90 degrees C and the sum of the radii of di-n-butyl phthalate and air molecules is proportional to T$^{-\frac{3}{4}}$. From the experiments in hydrogen the collision radius of di-n-butyl phthalate is 4$\cdot $68 angstrom at 19$\cdot $90 degrees C and from the experiments using Freon 12, 5$\cdot $24 angstrom at 19$\cdot $90 degrees C. The shape of the drops has been studied, and errors introduced by assuming a spherical shape are shown to be negligible.