A definite type of hydrometer with linear and fine stem and parabolic bulb is suggested. Before measurement, the hydrometer should be well calibrated. The contents of soil particles of different size can be directly determined at different time after sedimentation of particles. Grinding the soil sample for five minutes is available for mechanical dispersion of soil particles. 60 ml of 0.5 N NaPO₃ for 50 grams of soils is suggested for calcareous soils and 60ml of 0.5 N NaOH for 50 grams of soils is suggested for lateritic soils.