1). Up to this moment there are no criteria for a quantitative prediction of solubility of chemical compounds. Neither can we make this for such systems as M 1XM nX n−H 2O or for more complicated systems. There are often experimental data about change of solubility in systems of this type, however, a quantitative bond of solubility and system's composition is unknown, An isotherm of solubility for systems of this type is two lines on a plane system of coordinates and one on a cross point. 2). Our Experimental data for systems M 1X− M nX n−H 2O by solid phase as an ion exchanger are such that we can draw the following conclusions: a, transitions of M +-ion from the phase of zeolite is a stage which changes the energy of the systems a little; b, interactions M 1XM nX n with molecules of liquid phase of solute or interaction of solvate ions with one another is a basic contribution to a decrease in energy of the whole system. So, for the example, for systems Na-zeolite-Cl 2H 2O and Ca-zeoliteNaClH 2O in a region of high concentration solutions, the change of salt composition takes place along an isotherm of the system to the eutectic point. c, This result indicates indifference to the direction of approach to eutectic and, hence, a prevailing influence of interaction in liquid phase in comparison with the transition of a solid phase NaA to CaA or vice versa. 3). From this we can make following admissions. Let's consider that salt M 1X is a strong coordinating salt, if M +-ion has the more specific electrostatic charge in comparison with the charge of M n+-ion and vice-versa. Let's consider also, that a cation with the more specific charge corresponds to the more coordinative number. In the simplest approach a maximum coordinative number is equal to 6 and another number is 4. We can admit that a tetrahedron environment of cation M + is formed by bond of octahedron pair (1 octahedron = 1 tetrahedron cavity), and also from bond of 4 octahedrons (1 close tetrahedron cavity). 4). These admissions give the following results: 1 kg H 2O contains 6.02 × 10 23· 10 3:18:6 octahedrons, half of which has M +-ion and another half contains X −-ion. So, octahedrons contain 6.02 × 10 23 × 10 3:18:6:2 = 4.63 g M salt MX. This figure evidently determines the solubility of any octahedron coordinative salt of MX-composition. Another salt, M nX n, is found in open tetrahedron cavities, formed by octahedrons, bound in pairs and its solubility will determine 2.31 g M or 1.15g M, if ions of salt M nX n are found only in tetrahedron cavities, formed by 4 contacting octahedrons. In the first variant this leads to the following results for systems NaCl(M 1X)KCl(M nX nH 2O: 18.8 wt.% NaCl, 11.9% KCl. In the second variant: 19.9% NaCl, 6.4% KCl, while experimental data for 25 °C are: 20.4% NaCl, 11.1% KCl. 5). Similar results of solubility were also found for other chloride, sulphate and nitric systems of M 1XM nX nH 2O-type, forming individually soluble salts.