Simple apparatus for producing single liquid drops

Abstract

A simple experimental apparatus has been used to produce individual mercury and sodium amalgam drops in the size range of 0.3–2.5 mm diam. A high resistance to the flow of liquid was provided by a capillary tube. The cross section consisted of a 0.20 mm o.d. tungsten wire placed in a 0.25 mm capillary bore. By this method, flow rates of 1 μl/s and lower were obtained, which enabled the formation of drops as small as 1 mm diam in a time interval of 20 s. The drops were formed at a plastic tip, and on reaching the desired size, were stripped off by a stream of argon. An optical sensor was used to detect the growing drop and to switch on the argon stream at the desired time. The growth of the drops at the tip was observed using an image analysis system which showed good agreement between the observed and calculated drop sizes at various instants. The consistency in size from drop to drop, for any particular setting of the apparatus, was evaluated by analyzing magnified pictures of the drops as well as by measuring their weights. The variation in the drop size was found to be within ±2% of the mean value.