Hydrometer Analysis, Hydrometers, Hydrometer Water Baths

Hydrometer Analysis of Soil

Hydrometer Analysis – Particle Size Distribution of Soils Test, ASTM D422
Hydrometer analysis provides a quantitative evaluation of the particle-size distribution of the material that is smaller than 75μm (No. 200 sieve) found in typical evaluations of fine-grained soils. The test is used in conjunction with a standard sieve analysis of fine-grained soils with a wide range of particle sizes to provide a complete gradation curve. It is also used to more accurately evaluate the sedimentation or fines of a particular soil.

Hydrometer soil analysis is based on Stokes Law, which claims that the velocity at which a particle settles while suspended, all other factors being equal, is determined by the shape, weight and size of the particle. Because it is assumed that soil particles have the same specific gravity, it’s expected that larger particles will settle more quickly than finer ones in a soil-water suspension. By measuring suspended solids in sedimentation cylinders, hydrometers are able to measure a soil’s particle-size distribution.

To perform a hydrometer analysis the test specimen is combined with a dispersing agent and test water. This sample is then thouroughly mixed and placed into a cylinder with additional water. A hydrometer is then used to take readings at specific time intervals. The results of this test can then be combined with the sieve analysis to establish a complete gradation curve of the material or used to just evaluate the sedimentation or fines of the material.

Hydrometer analysis requires several items. These include soil hydrometers, hydrometer jar baths, constant-temperature water baths, soil dispersion mixers and sodium hexametaphosphate. All these items are available from Humboldt. We provide:

Hydrometer Analysis Set – Complete kit with all you need to determine the distribution of soil particles smaller than 75μm

Hydrometer Jar Bath – Unit is designed to hold eight Hydrometer Jars in a constant-temperature bath, which includes both heating and cooling

Soil Hydrometers – Measure the distribution of soil particle sizes by analyzing suspended solids in sedimentation cylinders

Hydrometer Jar – Graduated cylinders used to suspend solids for evaluation

Soil Dispersion Mixer – Method for dispersing soil suspensions for hydrometer analysis using high-speed mixing

Air Jet Dispersion Tube – Provides a method to disperse soil suspensions directly in the Hydrometer Jar

Dispersion Hand Stirrer – A handheld way to break up soil suspensions directly in the Hydrometer Jar

Visit our geotechnical testing and engineering landing page for more in-depth information or read our Hydrometer Analysis blog article.