The basic differences between mechanical analysis of sand by Ro-Tap sieving and by settling in a sedimentation balance are discussed. The Groningen balance can continuously and rapidly record settling times of the grains (50–1,000 μ) of a 1.5-g sample with a maximum recording and reading error of about 2%.

The theory of sieving is not fully developed yet, nor has the theory of settling of sand-sized particles been adequately expressed by any mathematical law. The drag coefficient (CD) and Reynolds number (Re) relation often used to derive diameter (d) from settling velocity (v) in this size range, are calculated from experimental data on diameter and velocity. Conversion of settling times to “sedimentation diameters” with the help of experimental curves for single, spherical quartz grains and their comparison with the corresponding “sieve diameters” are often found to be unsatisfactory in the case of natural sands, because shape and density variations of every individual grain in a sample can never be taken into account. Therefore, the use of settling velocity as a new grain parameter is advocated.