r.OARD 
 
 April 1951 ET-2C5 
 
 United States Department of Agriculture 
 
 Agricultural Research Administration 
 
 Bureau of Entomology and Plant Quarantine 
 
 A VIBRATORY APPARATUS FOR PRODUCING DRops 
 OF UNIFORM SIZE 
 
 1/ 
 
 By J. M. Davis, Division of Forest Insect Investigations—' 
 
 An apparatus for producing drops of uniform size has been developed 
 in connection with a recent laboratory study of the behavior of individual 
 drops within the size range normally encountered in insecticide sprays 
 applied from aircraft. The drops are formed on and removed from a 
 capillary by a vibrating finger at the rate of 60 drops per second. 
 
 Construction 
 
 A simple 6 -volt electromagnet (M in accompanying figure) is connected 
 in series with the secondary of an 8 -volt doorbell transformer, the 
 primary of which is fed from a variac off the 110-volt line. The finger 
 (F) is made from a piece of wire from a paper clip (diameter 0.036 inch) 
 about 1/2 inch long, approximately half of which is flattened knifelike by 
 hammering and filing. It is soldered to the end of a short length of 
 hacksaw blade (B^) with the flattened part projecting and with the flats at 
 right angles to those of the blade. The other end of the blade is fastened 
 to the base with a clamp so that the blade extends about 2 l/2 inches and 
 the free end bearing the finger is in front of the electromagnet. By 
 projecting the blade more or less beyond the clamp it can be made to 
 vibrate "in tune" with a 60-cycle current producing a 60-cycle-per- 
 second vibration, the magnitude of which can be adjusted by the variac. 
 
 A capillary {C) is drawn from a length of larger tubing (_T), the 
 undrawn part of which forms a reservoir for the liquid. The capillary 
 is held vertically in front of the finger by an adjustable support with the 
 tip of the capillary slightly below the level of the finger. Slide-control 
 mechanisms (K) make possible a fairly fine adjustment in the position 
 of the capillary relative to the finger. The magnitude of vibration is 
 best when the finger almost touches the capillary at its nearest point of 
 
 1/ In cooperation with the Division of Farm Machinery, Bureau of 
 Plant Industry, Soils, and Agricultural Engineering. 
 
approach. Usually it is also necessary to apply a slight, controlled air 
 pressure to the surface of the liquid within the reservoir. A water bubbler 
 teed into the tube G is used to control this pressure. The water bubbler 
 consists of a glass tube through which the excess air flow is allowed to 
 escape under water. It has seldona been found necessary to apply a 
 pressure of more than a few inches of water. 
 
 Operation 
 
 Slow-motion movies of the apparatus in operation show that the 
 following action takes place during one cycle (1/60 second) in which one 
 drop is produced. Liquid is forced out of the capillary by the pressure 
 behind it until a small drop begins to take shape. Early in its formation 
 this drop rises on the outside of the capillary and makes a sort of torus, 
 or ring, around it. It does not rise far, but takes up a stationary position, 
 where it increases in size by the addition of material from the capillary. 
 The correct vertical position at which to adjust the capillary is with the 
 finger at the level of this torus. The finger approaches until it makes 
 contact with the torus; then the drop begins to transfer to the finger. 
 However, because of the high acceleration of the finger the material 
 drops off as the finger recedes. 
 
 When properly adjusted, uniform drops arc produced at the rate of 
 60 per second, the succession of drops streaming in a single line as they 
 leave the apparatus. The stream seldom falls directly downward but 
 usually is projected outward. It is seen most easily when a light beam 
 is played upon it. The drops are so nearly uniform in size that measure- 
 ments under the microscope reveal no variation. When these drops are 
 of oil, and are collected on a film of water, they will arrange themselves 
 in perfectly aligned rows. This action would take place only if the drops 
 were uniform. By using various sizes of capillaries and different pres- 
 sures it has been found possible to make oil drops of any desired diameter 
 between 6 and 140 microns. The machine has been used only on oil 
 solution. 
 
UNIVERSITY OF FLORIDA 
 
 3 1262 09242 9439