The settling of the solid particles through a liquid either to produce a concentrated slurry from a dilute suspension or to clarify a liquid containing solid particles. Usually this relies on the force of gravity, but if the particles are too small or the difference in density between the solid and liquid phases is too small, a centrifuge may be used. In the simplest case the rate of sedimentation is determined by Stokes’ law, but in practice the predicted rate is rarely reached. Measurement of the rate of sedimentation in an ultracentrifuge can be used to estimate the size of macromolecules.