A COMPARISON OF METHODOLOGY IN PARTICLE SIZE ANALYSIS

The ‘particle size' of a soil or sediment sample typically refers to the relative percentage of sand, silt and clay in the sample. Because of the important role that particle size plays in surface erodibility, hydrology, cation exchange, and nutrient availability, numerous environmental and engineering industries rely on laboratory procedures which produce accurate and precise particle size results. Few if any studies, however, have compared the results of traditional hydrometer and pipette methods with the results of more technologically advanced machines such as laser particle counters and sedigraphs. Here we measure the particle size for approximately 100 samples using a standard pipette method and the Spectrex laser particle counter (LPC) in order to compare their results. Duplicates were performed for each method on every 12th sample to determine precision. For the pipette method, the <2mm air-dried fraction of soil is shaken in a solution of 10% Sodium Phosphate and distilled water. The solution is then wet sieved through a 63 um and this sand faction left in the sieve is oven dried and weighed. The remaining sediment is diluted, shaken, and allowed to settle in 1000 mL flask for the recommended time period. Using Stoke's Law, an alloquot is removed at the appropriate time and the clay content is determined once dried and weighed. The sand weight and clay weight are then subtracted from original total weight of 25 mg for each sample to give us the silt weight and the sample is then ready for statistical analysis. For the LPC, after an alloquot of the solely clay solution is removed following the above procedures, additional 16 mL sample of the clay and silt solution is taken after it has been shaken thoroughly That 16 mL sample is then double or triple diluted with store bought purified water and then put into the laser chamber of particle counter. The laser refracts light off the different particle sizes and counts each to give us a full description of the particle sizes from 0 to 63 um.Preliminary results indicate that the two methods have comparable (within 0.05%) precision and accuracy.