Abstract: Numerous Physical Chemistry textbooks employ the ethylene nitrile-water-ethanol system to illustrate ternary phase diagrams with two pairs of partially miscible liquids. However, two significant concerns have emerged: first, regarding the actual existence of the compound termed “ethylene nitrile”, and second, whether the phase diagrams accurately represent the characteristic solubility changes with decreasing temperature. Since phase diagrams are constructed based on experimental data, it is essential to provide the systematic nomenclature and molecular structure of “ethylene nitrile” to ensure the correct compound can be obtained for experimental verification. The accuracy of phase diagrams directly impacts their reliability in practical applications, thus warranting careful examination of discrepancies among diagrams presented in different textbooks.

Key words: Ternary phase diagrams, Partially miscible liquids, Ethylene nitrile, Temperature effect