A New Type of Invariant Points in Multicomponent Diagrams of Solubility According to the Example of the Na+,Ni2+//Cl−,\({\text{SO}}_{{\text{4}}}^{{{\text{2}} - }}\)–H2O System

The authors describe a new type of invariant points on isothermal-isobaric solubility diagrams of multicomponent systems. Such invariant points are directly related to the crystallization of solid phases based on pure solvents at temperatures below those of the latter in single-component systems. The type of nonvariant processes that occur at the indicated points during the isothermal evaporation of the solvent are considered, along with the stability of monovariant equilibria in the immediate vicinity of nonvariant points. Typical examples of such non-variant equilibria are presented using three- and four-component (mutual) water-salt systems as an example.