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