This International Standard specifies methods for determining the particle size distribution of metallic powders by measuring the attenuation of an electromagnetic beam projected through a suspension of particles setting in a liquid under grivity.The methods are suitable only where Stokes´ equation is applicable, i.e. laminar flow corresponding to a Reynolds number less that 0,25, and for particles whose setting rate is not affected by Brownian motion. They are therefore suitable for all metallic powders, including powders for hardmetals, containing particles in the size range 1 ym to 100 ym. They should not, however, be used fora) powders containing particles whose shape is far from equiaxial, i.e. flakes of fibres, except by special agreement;b) mixtures of powders;c) powders containing lubricant of binder;d) powders which cannot be dispersed in a liquid.These considerations set an upper and a lower limit on the size of particles to be tested by a sedimentation method (see 5.1).If the largest particle present in the sample exceeds this limit, the viscosity of the liquid needs to be increased to meet this requirement.Stokes´ law may be assumed to be valid for an initial concentration of the powder in the liquid of up to 0,5% (V/V). In some cases, higher concentrations of up to 1 % (V/V) still give correct results, but validation tests are necessary for each material.