The Measurement of Airborne Droplets by the Magnesium Oxide Method

Abstract

A complete calibration has been made for the first time of the method of detecting and measuring airborne droplets whereby the permanent impressions made when they strike a layer of magnesium oxide smoked on a glass slide are measured microscopically. A size range of 200 to 10 μ and a wide range of liquids and impact velocities were investigated, and it was found that the ratio of true drop size to impression size is constant at 0.86 for droplets > 20 μ of any liquid. The method fails below 10 μ. The calibration was made against an absolute method of droplet measurement, also against the so-called `focal-length' method. Droplets of any desired size were generated by a uniform spray apparatus.