ABSTRACT
There are several standard particles currently in scientific use. For example, uniformly sized spherical polystyrene latex particles are used as a calibration standard in electron microscope studies. Natural pollens and spores are also monosized and nearly spherical, but they are sometimes swelled by moisture and have irregular surfaces. For example, the diameter of lycopodium particles measured by means of a microscope is about 30 μm, whereas it is about 24 μm when a liquid sedimentation method is used, because of surface irregularities. A specially made precipitated calcium carbonate is also monosized and is cubic in shape.
