INVESTIGATIONS OF CHARGED WATER DROPS

Charged water drops, 50 to 120 microns in diameter, were suspended in a nonuniform ac field and studied with respect to loss of mass and loss of charge under normal evaporation and at electrostatic instability. Most of the work was conducted at or slightly above saturation of the air in the suspension chamber with respect to water vapor. Under these conditions, the drop shrinks to half its initial diameter in two or three minutes, whereupon it becomes unstable. The positive drop losses charge by neutralization by negative ions. Loss of charge and loss of mass occur in steps of alternating activity and inactivity. The loss of mass appears to be accelerated by condensation in the presence of positive ions. There is a large loss of charge but no measurable loss of mass, nor any measurable deformation of the drop, at instability. The rates of loss of charge and loss of mass in evaporation depend upon the presence of ions. It appears that ions are produced intermittently in the process, presumably in connection with condensation of water vapor. At instability a shower of small condensate droplets is formed in the vicinity of the drop when a slight supersaturation is maintained. It is concluded that evaporation is more complex than the mere removal and diffusion away of individual water molecules, and that electrification and ionization are essential elements of atmospheric process. (Author)