Pipette Method of Sedimentation Analysis for Particle Size Distribution

Pipette method is popular method to determine particle size distribution. It is based on Stoke's law.

What is sedimentation analysis?

Sedimentation analysis is based on Stoke’s law.

If sphere is falling in a medium of infinite extent, it’s velocity has been increased due to the gravity effect. After some times forces get balanced and it attains a constant velocity known as the terminal velocity

What are the different methods?

• Pipette Method
• Hydrometer Method

Procedure for Pipette Method

Take oven dried sample mix it with the distilled water. Remove the organic matter if present.

• If organic matter present then add hydrogen peroxide.
• To remove calcium add 0.2N hydrochloric acid.

Add deflocculant agent and mix thoroughly. After mixing the sample, start taking the observations.

• Collect a small amount of sample at different intervals like 30sec,1min etc.
• Insert the pipette at constant height He , generally 10cm, 10ml sample s drawn.

Calculation of finer particles

Initially at t=0, concentration is the same everywhere, as we allow the time to pass (t1) solids start settling.

• Then some of the solids would have moved down to the height He.
• V=He/t.
• The particles whose velocity is greater than (He/t1) could have crossed it otherwise they will be under suspension above He.
• The particles which settle down below He, they have dia greater than He.
• Find %finer than dia of the particles at He

Summary Points

• Sedimentation analysis for particle size analysis is done by pipette and hydrometer method
• Sedimentation analysis is based on Stoke’s law
• There are limitation to Stoke's law
• We assumed the particles are spherical in shape but in practical clay is flaky in shape.
• We have assumed the medium has no boundaries and infinite but we perform the test in a finite medium and there exist many spheres