Liquid Mixtures

(liquid systems), physicochemical systems that preserve the liquid state for any ratios of the components and in a definite temperature interval. The liquid systems that have been studied in the greatest detail consist of two components (binary liquid systems). The mutual solubility of two liquids at given temperature and pressure may be unlimited (for example, water and ethyl alcohol, benzene and toluene), limited (for example, at 20°C, 6.48 percent by weight of diethyl ether is soluble in water, whereas 1.2 percent by weight of water is soluble in diethyl ether), or virtually nonexistent (for example, water and mercury). The mutual solubility of two liquids increases with increasing or decreasing temperature and becomes unlimited upon reaching the upper or lower critical solution temperature, respectively. The vapor pressure of binary liquid systems is described by the Konovalov and Vrevskii laws. The viscosity isotherms of binary liquid systems are almost straight lines if the components are neither associated nor dissociated and do not form chemical compounds. In the case of formation of an undissociated compound, the viscosity isotherm consists of two branches, which intersect at the singular point, whose abscissa corresponds to the composition of the compound (N. S. Kurnakov and S. F. Zhemchuzhnyi, 1912).