Studies of Equilibrium Solid Solutions in Ionic Lattices Systems: KMnO4–KClO4–H2O and NH4Cl–MnCl2–H2O

Abstract

1. The systems, potassium permanganate‐potassium perchlorate‐water and ammonium chloride‐manganous chloride‐water, have been studied at equilibrium conditions by phase rule and x‐ray diffraction methods. 2. The system potassium permanganate‐potassium perchlorate‐water yields a continuous series of solid solutions having orthorhombic crystal symmetry. For these, the components of which are of similar crystal and chemical structure and of identical valence type, Vegard's additivity law is followed by the a 0 and c 0lattice constants, but the b 0 constant shows a definite deviation. 3. A method is described of obtaining homogeneous crystals with a particle size which gives excellent powder diffraction photograms in cases where heat annealing is not feasible. 4. A method of analyzing for ClO4 — is given. 5. The danger of making serious errors is pointed out in the use of rapid precipitation by chemical reaction or from supersaturated solutions as a method of preparing solid solutions for the study of the relationship between their lattice constants and composition. 6. The system ammonium chloride‐manganous chloride‐water shows three solid solution series; the crystals obtained in the first series have cubic symmetry, while in the others the symmetry is tetragonal. 7. The mechanism of the formation of the ``anomalous'' solid solutions between ammonium chloride and manganous chloride is given. Experimental and other considerations verify it. 8. It is shown that Vegard's law is not followed by the first solid solution series in which the components are of dissimilar chemical and crystal structure and dissimilar valence types. The curve for the relationship between the lattice constants and composition rises to a maximum and then falls off. Reasons to explain why this law does not apply to these solid solutions are given. 9. The existence of a new ``compound,'' 6NH4Cl·MnCl2·2H2O, is demonstrated. This and the known compound, 2NH4Cl·MnCl2·‐2H2O, are considered to be examples of ``compounds of variable composition.'' They are tetragonal with a 0 = 15.256±0.004A, c 0 = 16.008±0.007A and a 0 = 7.5139±0.0005A, c 0 = 8.245±0.003A, respectively. The structure of the latter is that of 2NH4Cl·CuCl2·2H2O which belongs to space group D 4 14 h or P4mnm.