Abstract
The flattening coefficient, F, which is the ratio of apparent droplet diameter as measured on a microscope slide to the true diameter of a spherical drop, has been determined for particles of oleic acid and DOP aerosols collected on treated slides. The slides were made oilphobic by immersion in a widely used fluorocarbon surfactant (NYEBAR Type CT or 3 M Co. Chemical FC-721). The mean value of F for oleic acid was found to be 1.34, and for DOP, 1.35. There is no apparent variation of F with particle diameter for aerosols in the 2.7−29.1 µm range. For DOP, a single technique was used to measure F1 and for oleic acid three techniques were employed. The different techniques gave essential the same result for oleic acid. The addition of a commonly used fluorescent analytical tracer, sodium fluorescein, to oleic acid in amounts of 5–20 percent (m/v) causes a slight shift in the flattening coefficient. With 10 percent uranine, the value of F is 1.32.