  We have shown in this investigation that the partial pressure can be defined
uniquely as each wall pressure exerted by a component in liquid mixtures, and
is an important observable physical quantity. As a consequence of this
definition, the law of partial pressures is applicable to liquid mixtures with
strong interactions. Furthermore, it has been shown here that the gas-liquid
phase equilibrium in mixtures is established by the balance of each
partial-pressure for every component between the two phases. Hence, for a
dilute solution Henry's law, Raoult's law and van't Hoff's law can be derived
on the basis of the concept of partial pressure.
