KINETICS OF WETTING IN WASHOUT OF DUST
283
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Fig. 1—Experimental setup for coalescence between two water drops.
sible to determine the actual instant of wetting because the wire end
was hidden by the water.
The solid was pushed against the drop at a speed of 125 cm/sec.
Photographs were taken of the event at 26,000 frames/sec. Thetotal
exposure time was approximately 10 msec. There was approximately
7 msec of useful exposure time(i.e., time after establishment of con-
tact).
A typical sequence of frames is shown in Fig. 2. The phenomenon
is very Similar to that observed with a pair of liquid drops. Onefirst
sees a slight flattening of the drop and later a thin lens at the interface.
This lens then spreads over the drop. The first appearance of the lens
is taken as the indication of wetting or coalescence. The formation of
a bond between the drop and the solid is thus indicated by a disturbance
of the drop surface. The flattening of the drop is not very pronounced
in the frames shown in Fig. 2. Other frames, taken in cases of no