ABSTRACT

The fall velocities of the boundaries of a series of well sorted samples of sand sized glass spheres were determined in a modified Emery type settling tube for the purpose of measuring the changes in mass fall velocities with changes in sample weights. Fall velocities of the faster falling, larger diameter spheres forming the leading boundary in each sample were found to increase with sample weight. Fall velocities of smaller spheres forming the slower or trailing boundary were found to decrease with increasing sample weights. Over the median diameter range of 0.784 to 0.383 mm these velocity changes appeared to be relatively independent of particle diameters, but at smaller median diameters the relative changes in velocity increased with decreasing size. From the weight-velocity rela ionships, it was shown that fall velocities achieved by masses of spheres depend upon the amount of sample used. Boundary velocities were attributed to certain particle diameters to provide a measure of the effects of the falling system on given sized spheres. It appeared further that the velocity of a given particle settling in a sample depends upon the size limits and the sorting of the sample. It was concluded that settling methods of analysis of sands do not give an accurate picture of size distribution in terms of sedimentation radii if the fall of the particles creates turbulence in the system.