Specific gravity tables are used to determine the specific gravity, or relative density, of a substance, which is the ratio of the density of that substance to that of a known substance, usually water. Water is known to have a specific gravity of 1.0 at 4 degrees Celsius.
Comparing the specific gravity of another substance to water determines whether the object floats. If the specific gravity is less than 1, the object floats; if greater than 1, it sinks. Additionally, since the specific gravity for every element is unique, that element displaces a specific amount of water if it sinks. This information helps identify unknown substances.
Many industries prepare specific gravity tables for substances they frequently encounter. For example, jewelers have such tables for gemstones and precious metals. If a jeweler wants to determine whether a metal sample is genuine gold, he can look up the relevant information on a specific gravity table and make a determination based on the amount of water it displaces.
Specific gravity tables and relative density have other useful applications. Shipbuilders use this information to determine which materials to use to build boats. Mechanics check battery acid and radiator fluid levels in automobiles with instruments that rely on these principles. Specific gravity even helps lab technicians analyze urine samples to determine whether kidneys are processing water properly.