The rate of evaporation of droplets; evaporation and diffusion coefficients, and vapour pressures of dibutyl phthalate and butyl stearate.

The rate of evaporation of drops of dibutyl phthalate and butyl stearate of radius approx. 0*5 mm. has been studied by means of a microbalance over a range of atmospheric pressures down to approx. 0*1 mm. of mercury. Wide departures from Langm uir’s evaporation formula were found to oceur a t these low pressures, bu t results are in good acoordance with the theory of droplet evaporation advanced by Fuchs which hitherto has not been tested experimentally. This experimental verification of Fuch’s theory for droplets of medium size evaporating a t low pressures shows th a t the theory can be applied to the evaporation of very small drops a t atmospheric pressure. The vapour pressures of the above liquids have been measured by Knudsen’s m ethod and th^ evaporation and diffusion coefficients calculated f ro n the experi­ mental data.