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.

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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.

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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

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