Relative density Wikipedia
Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water at its densest (at 4 #176;C or #176;F); for gases, the reference is air at room temperature (20 #176;C or 68 #176;F). The term quot;relative densityquot; is often preferred in