A sedimentation balance for particle size analysis in the sub-sieve range

A method is described for estimating the particle size distribution (Stokes' diameters) of insoluble powders in the sub-sieve range. The powder is dispersed in a suitable liquid and the particles allowed to settle on to the pan of a torsion balance. The cumulative weight settled is read at chosen time intervals by direct deflexion of the torsion wire. An alternative method is to use the return twist of the torsion wire. The size distribution by weight within the particulate mass is deduced from the curve relating the cumulative weight with time, the procedure adopted for calculation being described. The method is simple and speedy and can be operated by relatively unskilled labour.