A new conditional expression has been proposed from the viewpoint of equilibrium thermodynamics for attaining a steady state with no existing flow of matter (static steady state) in a system which is not uniform in temperature and pressure. The conditional expression has been applied to a binary system under a uniform pressure, and it has been shown that the heat of transport can be related to the dependence of the standard entropy and the activity on temperature, and that it is possible to

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... nd activity data of a solution into a wider temperature range by conducting experiments to attain the above-mentioned steady state in a system under a uniform pressure.