Washington DC 1st Class Boiler Practice Test

Specific gravity describes the ratio of the weight of a liquid to the weight of an equal volume of water at the same temperature. Because weight is mass times gravity, and gravity is the same for both samples, this ratio is effectively the same as the ratio of their densities. In other words, specific gravity is the density of the liquid divided by the density of water at that temperature, a dimensionless number that shows how heavy or buoyant the liquid is relative to water. We use water as the reference point precisely because its density changes with temperature, so the comparison must be made at the same temperature. This concept differs fromDensity, which is an intrinsic property of a substance, as well as from viscosity and refractive index, which describe flow resistance and light-bending behavior, respectively.