A Modified Hydrometer Procedure for Particle Size Analysis

Day's hydrometer method (1965) is theoretically sound and accurate for particle size analysis, but it is less time efficient which deters its use in routine analysis. A simple modification of the Day hydrometer method has been suggested which considers decay of suspension density proportional to square of particle size and combines Stoke's law. This results in a predictive equation that gives the hydrometer reading as a function of time as follows: where Rj is hydrometer reading at time tj (g/litre); Ri, is initial hydrometer reading at time ti (g/litre); a and b are empirical constants, and B is the slope of the line indicating the relationship between log (a/b - Rj) and log (tj/ti). The procedure used to obtain different constants is given. The results show that the modified Day hydrometer method takes only 2 h to analyze a soil sample as compared to 8 h with Day's hydrometer method. The modified procedure is not only time efficient but is also theoretically sound, accurate, and yields consistent results.