A hydrometer is a laboratory instrument used to measure the specific gravity (relative density) of liquids, which is the ratio of the density of the liquid to the density of water. Hydrometers are commonly used to determine the concentration of dissolved solids in solutions, such as acids, bases, and sugar solutions. They are also used to determine the alcohol content of fermented beverages, such as beer and wine.
A hydrometer typically consists of a cylindrical glass tube with a bulb at one end that contains a weighted material such as lead shot, mercury, or tungsten. The hydrometer is placed in the liquid to be tested, and the degree to which it floats indicates the liquid's specific gravity. The specific gravity is read from a scale on the hydrometer where it intersects with the surface of the liquid. Some hydrometers also have a thermometer built in to correct for temperature variations that can affect the accuracy of the readings.
Hydrometers come in various ranges and are designed for different purposes. For example, a Baume hydrometer is used to measure the specific gravity of liquids lighter than water, while a salinity hydrometer is used to measure the concentration of salt in seawater. There are also digital hydrometers that use electronic sensors to measure the specific gravity of a liquid.
Hydrometers are widely used in many industries, including food and beverage, chemical, and pharmaceutical. They are also used in home brewing and winemaking, as well as in aquariums to measure the salinity of saltwater.