The Soil Hydrometer is a buoyant glass tube calibrated to measure the relative density of liquids. They are typically calibrated and graduated with one or more scales such as specific gravity. A hydrometer usually consists of a sealed hollow glass tube with a wider bottom portion for buoyancy, ballast such as lead or mercury for stability, and a narrow stem with graduations for measuring. The Soil Hydrometer is very efficient and safe for use. It is very accurate.