Coordinates used mainly in representation of multicomponent phase diagrams that distinguish solutes and a single solvent. The mole or mass fractions of the \(s\) solutes are chosen as the primary composition variables and the mole or mass fraction of solvent as a secondary variable, so that the solute amount (mass) fractions may be represented, for example, in ternary and quaternary systems, as linear (ternary) or planar triangular or square planar (quaternary) diagrams, with the solvent amount or mass fraction along an axis perpendicular to the chosen diagram of solute variables. Quantitatively, \[x_{{\rm{s}},{\ce{B}}} = x_{\ce{B}}/\sum \limits_{i=1}^{s}x_{i}\] where the summation is over the \(s\) solute substances. Note that \(\sum \limits_{i=1}^{s}x_{{\rm{s}},{\ce{B}}} = 1\).