Description of a van't Hoff apparatus A "van't Hoff apparatus" is mentioned as a means of performing a reaction involving gases in a reversible manner, for instance here. 

Unfortunately I have been unable to find a description of such a device using a web search (including on this site). It may be that the device has other names. I intuit from the post above that the apparatus is similar to the device used to measure the Joule-Thompson coefficient of a gas.

Could someone provide a description of the nature and operation of such an apparatus (even if it is only a theoretical device)?
The Van't Hoff equilibrium box is a chamber containing a mixture of reactants and products at equilibrium.  It is connected to an array of cylinders, each containing one of the pure reactants or products.  The chamber itself is operated at constant total pressure and temperature.  The cylinders are each connected to the equilibrium box through a semipermeable membrane that only passes that species into the chamber.  Pure species are introduced in stoichiometric proportions to the chamber through these membranes at the same partial pressures as in the reaction mixture, and pure products are removed in stoichiometric proportions at the same partial pressures as in the reaction mixture.  So the operation of the equilibrium box is reversible, and the delta G in going from pure reactants in to pure products out is zero.