SPECIFIC GRAVITY (SG OR SP GR)

(1) The ratio of the density of a substance to the density of some substance (as pure water) taken as a standard when both densities are obtained by weighing in air. (2) The ratio of the mass of a solid or liquid to the mass of an equal volume of distilled water at 4°C (39°F) or of a gas to an equal volume of air or hydrogen under prescribed conditions of temperature and pressure. Relative to water, the specific gravity (SG) is given by: SG = p/pw; where p is the density (weight per unit volume) of the unknown substance and pw is the density of water. The parameter has no units and is frequently used to determine the concentration of a Solution.