Final answer:
A hydrometer test is conducted for characterizing soil finer than the #200 sieve.
Step-by-step explanation:
A hydrometer test is conducted for characterizing soil finer than the #200 sieve. A hydrometer is an instrument used to measure the specific density of liquids. It consists of a sealed hollow glass tube with a wider bottom portion for buoyancy, a ballast for stability, and a narrow stem with graduations for measuring. By gently lowering the hydrometer into the liquid, the point at which the surface of the liquid touches the stem correlates to relative density.