# Methods to Measure Particle Size

The particle size measurement of a powder, or granular material, or particles dispersed in fluid, is a list of values or a mathematical function that defines the relative amounts of particles present, sorted according to size.

__Methods to measure particle size__

The **particle size measurement** of a powder, or granular material, or particles dispersed in fluid, is a list of values or a mathematical function that defines the relative amounts of particles present, sorted according to size.

The major Methods for particle size measurement are:

1) Microscopy

2) Sedimentation

3) Sieving

### 4) Air elutriation analysis

### 5) Electro resistance counting methods

6) Light & x-ray scattering

7) Permeametry

8) Particle Trajectory

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**1) Microscopy**

It is the most direct method for size measurement. Its lower limit of application is determined by the resolving power of the lens.

For white light, an ordinary microscope is used to measure particles from **0.4-150μ.**

With special lenses & ultraviolet light, the lower limit may be extended to **0.1 μ.**

In the ultra microscope, the resolution is improved by use of dark field illumination. The size range of the ultra microscope is from** 0.01-0.2 μ.**

The diameter of the particles on the slide is measured by means of a calibrated filar micrometer eyepiece. The hairline of the eyepiece is moved by the micrometer to one edge of a particle & the reading on the micrometer is recorded. The hairline is then moved to the opposite side of the edge of the particle being measured & the micrometer is read. The difference b/w the two readings of the diameter of the particle. All of the particles are measured along an arbitrary fixed line.

Graticules or eyepiece with grid of the circles & squares are used to compare the cross-sectional area of each particle in the microscopic field with one of the numbered patterns. The number of particles that best fits one of the numbered circles is recorded. The field is changed & the procedure is repeated until the entire size range is covered.

In both techniques, the magnification is determined by the use of a calibrated stage micrometer as the magnification is not equal to the product of the nominal magnification of the objective & the eyepiece.

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