https://doi.org/10.1351/goldbook.F02494
In general, a ratio of two quantities of the same kind, the numerator quantity applying to one @C01281@ (or part) of the system and the denominator to the sum of quantities for all constituents (parts) of the system. When applied to mixtures fractions represent a group of 3 quantities: @M03722@, @V06643@, and @A00296@ (or @A00296@ equal to the @N04265@).