A standard method for measuring the size of small particles. Sediment is stirred into suspension in a measured volume of water in a sedimentation tube, aliquots of uniform size are withdrawn by pipette at specified intervals and depths, oven-dried, and weighed. The grain diameter (D) is then calculated by D = √C/√(x/t), where C is a constant depending on the particle density and density and viscosity of the fluid, x is the depth (in cm) from which the particles are withdrawn, t is the time elapsed (in seconds), and x/t is the settling velocity.