State the Pipette Method of soil

The   sieve analysis, though is a true particle size analysis, is  unable to separate particles smaller than 20 microns. Such particles are separated by the pipette method or the sedimentation technique . This method is based on the principle that when soil
particles are suspended in water, they tend to sink.  Since there  is little variation in the density of most soil particles, then according to Stokes law the velocity (V) of settling (also called sedimentation velocity) is proportional to the square of radius (r) of each
particle i.e., V = kr² where k is a constant.  Co nsidering the velocity as distance of fall (h) / time ( t), we can calculate the travel time for a given diameter of soil particle for a fixed distance (say 10 cm). At the stipulated time a small aliquot of the suspension is pipetted out from the designated  distance, oven dried (100  - 105°C) and weighed to find out the amount of a particular fraction.