THE “Madelung term” referred to by Ladd (and used throughout his treatment 1,2 as the sole electrostatic component of his “crystal energy”) in an energy term, expressed in electron units2 A−1, whose magnitude corresponds to the energy change Open image in new window where Qc and Qoare the previously denned fractional charges on the complex ion3. The energy of process (1) was designated UM our article and as A(L)/Lin Ladd's formulation. Ladd1 fails to recognize that an hypothetical ion gas consisting of Ca2+, CQc and OQO species constitutes neither a real thermodynamic energy level nor a real state of the system and, as such, cannot be employed as part of a thermochemical cycle, such as the Born-Haber cycle and hence cannot be directly related to observable thermochemical quantities. The role of the term, UM, in Ladd's work is a dominant one. In our work it rightly fulfils a purely transitory role, its calculation constituting nothing more than a convenient stage in the mathematical evaluation of the thermodynamically significant energy change, UElcc, which corresponds to the process Open image in new window