STANDARD PROCEDURE IN THE HYDROMETER METHOD FOR PARTICLE SIZE ANALYSIS

In a widely-used method for particle size analysis of soils, the weight percentages of sand, silt, and clay are calculated from the density of an aqueous soil suspension measured by hydrometer. There are many versions of the procedure, differing in the type of dispersing solution, the volume of the suspension, the time of settling before taking hydrometer readings, or in the method of correcting the raw readings. Our procedure avoids errors inherent in some versions of the method, which can cause discrepancies from expected values. The details of our procedure should interest those concerned with minimizing confidence limits in inter-laboratory surveys and with providing reliable particle-size distribution data to laboratory clients.