areometer

An areometer is a scientific instrument used to measure the specific gravity of liquids. Specific gravity is the ratio of the density of a substance to the density of a reference substance, usually water. Areometers work based on Archimedes' principle, which states that a body submerged in a fluid experiences an upward buoyant force equal to the weight of the fluid displaced by the body.

The instrument itself typically consists of a sealed glass tube with a weighted bulb at the bottom and a graduated stem at the top. When placed in a liquid, the areometer sinks until it displaces a volume of liquid whose weight is equal to the weight of the areometer. The depth to which it sinks indicates the specific gravity of the liquid. Liquids with a higher density (and therefore higher specific gravity) will cause the areometer to float higher, while less dense liquids will cause it to sink deeper. The markings on the stem are calibrated to directly read the specific gravity or, in some cases, other related properties like the concentration of a dissolved substance.

Areometers are used in various fields, including brewing and winemaking to determine the sugar content of wort or must, in the automotive industry to check the charge of a battery by measuring the specific gravity of the electrolyte, and in laboratories for general density measurements. Different types of areometers are designed for specific applications and ranges of specific gravity. For example, a hydrometer is a type of areometer specifically designed to measure the density of liquids, particularly water.