Hydrometer Under The Microscope

Abstract

For many years the hydrometer was the only technique that was internationally standardised for geotechnical particle size distribution analysis of fine soils. Nettleship et al. (1997). Recently Britain has added the pipette method as a preferred alternative. The pipette method is considered to give slightly more accurate and consistent results. Both procedures stand on the theoretical foundation of Stokes’ law. Stokes’ law assumes constant density of the particles being tested, that larger particles settle faster than small particles when in a liquid suspension, and that there is no interference between particles and other particles or obstructions in the suspension. It also assumes all particles to be spherical. This paper studies the hydrometer theory by analyzing settled sediments and compares the effectiveness of two dispersion procedures, namely that specified by TMH 1, with that specified by SANS 3001 (replaced TMH1).