Hydrometer Method of Sedimentation Analysis for Particle Size Distribution

Hydrometer method is a popular method to determine particle size distribution. The He in the pipette method is not constant here; It keeps varying

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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 Hydrometer Method

The He in the pipette method is not constant here. It keeps varying.

• Here it is not required to draw the sample like in pipette method, we can directly take the specific gravity of the solids using the hydrometer.
• This device works on the principle of buoyancy


Corrections to the hydrometer readings

Meniscus correction Cm
• The correction is positive.

Temperature correction
• If the temperature is greater than 27deg then positive
• If the temperature is lesser than 27deg then negative correction.

Deflocculating agent correction Cd
• The correction is negative.

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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