Definition - What does Thermohydrometer mean?
A Thermohydrometer is a specially designed hydrometer that is used for measuring specific gravity or the relative density of crude oil and petroleum products. There are various types of hydrometers used for measuring the specific gravity of the liquids; however, thermohydrometers are only used in the petroleum industry. This hydrometer is similar to a thermometer and consists of a cylindrical stem and a weighted bulb thus makes it float upright when used for measurement of specific gravity.
Petropedia explains Thermohydrometer
A Thermohydrometer measures the specific gravity of crude oil and petroleum products. The specific gravity here refers to API gravity. The higher the API gravity of crude oil, the lighter and sweeter it would be and thus yields large volume of valuable petroleum fractions in terms of their market price for a refinery. These valuable petroleum fractions or products are Naphtha, Gasoline, Diesel Oil, and Kerosene.
This hydrometer is made up of glass and consists of a cylindrical stem and a weighted bulb which is filled with mercury or lead shot. This helps in making it float upright. It comes with a cylindrical container called "Graduated Cylinder” in which the sample of petroleum liquid that needs to be tested for its API gravity is poured and the thermohydrometer is lowered gently into this filled container until the hydrometer floats freely. The temperature at which the tests are conducted is generally 60º F. The mercury or the lead shot rises because of this temperature and the point at which it stops corresponds to the specific gravity of the petroleum liquid.