Andreasen settling bottle

In the Andreasen settling bottle , samples are taken at fixed time intervals at a given level in the suspension. At any given time, particles with a critical size have just settled from the surface of the suspension past the detection level. Particles finer than this are still present at the detection level at their original concentration, while particles coarser than the critical size are not present. The critical size corresponding to each sampling time can be foimd using Stokes law, and in this way the cumulative size distribution can be calculated directly from the particle concentrations in the samples. 

As an alternative to sampling, optical detection of the tiu bidity of the suspension as a function of height and time is sometimes practiced. This is much less labor intensive than sampling, but, in contrast to the Andreasen settling bottle, a calibration is necessary. 

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