troduction
The hydrometer analysis, also called sedimentation method, is used to determine the grain
size distribution for the fraction of soil that is smaller than the No. 10 (2.00 mm) sieve. Fine soil
particles are dispersed by soaking the soil sample in a dispersing agent and by rapid stirring to
neutralize the charges between the soil particles. The test uses a Type 152H hydrometer
calibrated to give the mass of solids with specific gravity equal to 2.65 in suspension and the
settling velocity of the dispersed soil particles. The soil grain diameter D (mm) is computed by
application of Stokes’ Law, a theoretical equation for the terminal settling velocity of spheres in
a fluid, according to the following equations