X-ray diffraction data for three aqueous solutions of MgCl₂ were analyzed. It is shown that in a very concentrated solution the structure and correlation functions can be reproduced almost completely by using a nearest-neighbor model of ionic hydration, whereas in the more dilute solutions a certain number of interactions between the hydrated cation and external water molecules must also be considered. The mean coordination geometry for the close hydration was found to be octahedral both for cation and anion with mean cation-water distances (2.10-2.12 Å) and mean anion-water distances (3.11-3.14 Å) in accordance with results found in other cases.

The intensities of two-dimensional reflections from a non-graphitic carbon were correctly calculated by using the general Debye scattering equation and the hypothesis of small (about 12 Å in diameter) domains diffracting incoherently with respect to one another.

It is shown that the discrepancy in the first peak position between atomic and electron radial distribution functions for water is not ascribable to termination effects but is inherent in the different nature of the two functions.

Alkali halide aqueous solutions (LiCl, LiBr, NaCl, NaBr) have been investigated by X-ray diffraction in order to clarify the structural features of these systems (the existence of ordered local structures, their stability, geometry, etc.). The cation-H₂O interaction is particularly evident for the Li⁺ ions, for which a well resolved peak at 2.1 Å is apparent in the correlation function. It is shown that the ions give rise to a considerable disturbance of the solvent structure, in fact the `order range' in the solutions appears to be shorter than in pure water. The high coordination numbers of the Cl^- and Br^- ions could be due to close packing of solvent molecules or hydrated cations around the anions.

A general computer program for the analysis of X-ray diffraction data for liquids is here described. It consists of a central part (main) and a number of subroutines, in which one single step of the elaboration of experimental intensities is performed. This arrangement allows the entire sequence of operations to be performed as far as the radial distribution functions; alternatively only a part can be performed, starting or stopping at any point. The program is flexible and easily modifiable for the user's needs.