A hydrometer is made up of two words, hydro + meter, where hydro means water (or liquid) and meter means a scale. So, a hydrometer is used to measure some characteristics of liquids, i.e., specific gravity or relative density (density of liquid divided by the density of water). Hydrometers are filled with liquids like mercury (as in thermometers) or lead. During its use, it is placed in a container containing the liquid.
Definition: An instrument used to measure specific gravity or relative density of liquids which works on the principle that a solid body displaces its weight when placed in water and hence floats, also known as buoyancy, is called a hydrometer.
A Hydrometer Placed in a Liquid
The value at the surface of the liquid provides the specific density of the liquid. The value of specific gravity is unitless and expressed in decimals or percentages.
Diagram of Hydrometer
Types of Hydrometers and their Uses
Lactometer is used for milk.
Alcoholometer for wines and alcohols.
Saccharometer for sugar.
A barometer for tanning liquids in leather-making.
Acidometer for acids.
Salinometer for liquids with salt content.
Urinometer for urine analysis.
Thermo Hydrometer for fuel oils like petroleum.
Battery hydrometer for lead-acid battery.
Application of Hydrometer in Engineering
Use in Food Industry
Use in winemaking- A saccharometer and a thermometer is used to check the amount of sugar in wine or beer. The amount of sugar that is needed to put in can be determined by its specific gravity because it increases the density of solution. The alcohol content of the end product is determined by alcoholometer.
Hydrometers are also used in making ice-creams and brewers.
Use in Soil Analysis
In the engineering field, the analysis of soil involves another important use of hydrometers. It is used in determining the distribution of soil particles.
Hydrometer Uses in Laboratory
Different types of specialised hydrometers are employed in different matters. All research is first done in laboratories, so the use of hydrometers in laboratories is varied.
1. What is the special type of hydrometer which is used in checking the alcohol content in wine or beer?
Ans: The specialised hydrometer used for checking alcohol content is alcoholometer.
2. What do you understand about the relative density of a liquid?
Ans: Relative density of a liquid means density of liquid divided by density of water.
3. In what units is the specific gravity measured?
Ans: Specific gravity does not have any unit, it is unitless.
A hydrometer is an instrument used to measure the relative density or specific gravity of a liquid. It is of great importance for our day-to-day life as it is used in various industries which are crucial for our health. There are different types of specialised hydrometers which are named after their use.