In this group, we have the static-analytic methods, the quasi-static method (circulated phases) and the static-synthetic methods. The major advantage of static methods is their simplicity. The studied system is enclosed in a cell and one waits as long as needed to reach equilib- rium. An internal stirring system is usually added to the equilibrium cell in order to reduce the time of equilibration. The equilibrium can be checked by total pressure stability and/or constancy of phase composition as a function of time. Measurements are generally carried out isothermally, with compositions being determined after each pressure change to obtain isothermal p-x-y diphasic envelopes. Equilibrium is reestablished more quickly after a pressure change than after a temperature change, due to the thickness of the walls of the equilibrium cell, especially at very high pressures. We divide the closed-circuit methods into subgroups according to the way of the determination of the phase compositions.
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