Conclusions We have measured the evaporation rates of stationary single droplets by suspending them individually in an electrodynamic balance under precisely controlled con-ditions. By altering the total pressure of the surrounding gas, we have obtained the evaporation rates of the same droplets over a wide range of pressures (ie, 100 Torr> P> 1CT6 Torr). The ratio of the evaporation rate at a given pressure to that at high vacuum provides a direct mea-surement of the flux ratio J/Jk, thus eliminating the un-certainties associated with the estimation of flux Jk in the kinetic regime.

The results show that as the pressure decreases the evaporation rate increases to a maximum, beyond which a further decrease of pressure causes no change in the evaporation rate. The experimental evaporation rate data have been presented in terms of the flux ratio J/Jk as a function of the Knudsen number Kn. For Kn< 3.8, the