Hydrometer Analysis

What Is a Hydrometer Analysis?

A hydrometer analysis is used in determining the distribution of sizes of soil particles. Testing is done with specific products and different sedimentation methods to determine clay and silt fractions.
A hydrometer analysis will be used if the grain sizes are too small for a sieve analysis. In the case of fine-grained soil, the sieve analysis doesn’t give a reliable test result because there is a chance of lost samples during the process.
The hydrometer analysis is based on Stokes' Law. With this law, the velocity at which the grains will settle out of suspension with all the factors being equal is based upon the weight, size, and shape of the grain. With soil, it’s assumed that the particles are spherical and have the same gravity so coarse particles should settle quicker than fine ones.
A hydrometer is an instrument, which is used to measure the relative density of a liquid. It consists of two parts with a cylindrical stem and a bulb at the bottom. The lower the density of the specific liquid, the more the hydrometer will sink.