Order—Disorder Phenomena. V. Pippard Equations and the Phase Diagram for Ammonium Chloride

Abstract
The Pippard equations and the phase diagram for NH4Cl are analyzed in terms of a compressible Ising model. It is demonstrated that the Pippard relations are completely consistent with the occurrence of a first‐order transition in the immediate vicinity of a lambda point. In addition, the substantial variation in the slope of the order—disorder transition line with pressure can be well represented by this Ising model.