Principle of Andreasen Pipette Method
- The Andreasen Pipette Method is based on Stokes’ Law, which states that particles settle at a velocity proportional to their size in a fluid.
- Larger particles settle faster than smaller ones, allowing particle size distribution to be determined by sampling the suspension at fixed depths and times.
- The method is based on Stokes’ Law:
- $v = \frac{2 r^{2} (\rho_{p} – \rho_{f}) g}{9 \eta}$
Where:
Advertisements
- v = settling velocity
- r = particle radius
- = densities of particle and fluid
- = fluid viscosity
Construction
- Sedimentation cylinder: Tall, graduated glass vessel (500–1000 mL)
- Andreasen pipette: Precision pipette with stopcock, fixed at a set depth
- Stirrer: Ensures uniform suspension
- Thermometer: Monitors temperature
- Stopwatch: Times sedimentation
Advertisements
Working
- Suspension Preparation: Powder is mixed in water with a dispersing agent and poured into the cylinder.
- Sedimentation: The mixture is left still; particles settle at different speeds.
- Sampling: At set intervals, samples are drawn from a fixed depth using the pipette.
- Drying & Weighing: Samples are dried and weighed to determine the mass of particles remaining in suspension.
- Calculation: Particle sizes are calculated using Stokes’ Law, and a distribution curve is plotted.
Applications
- Soil texture analysis
- Ceramics and cement quality control
- Fine powder characterization in industries
Advertisements
