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In the course of thermal decomposition of the magnesium sulphate hydrates MgSO4.nH20 (n = 7; 6; 5; 4; 3; 2; 5/4; 1) the intermediate steps MgSO4.3H20, MgSO4.2H20, MgSO4.H20 and fl -MgSO4 are observed under quasi-isothermal and quasi-isobaric conditions at p ~ 0.1 MPa dependent on the water contents. The structure of the obtained monohydrate phase is identical with that of kieserite. Thermal decomposition of the magnesium sulphate hydrates is essentially influenced by the water vapour partial pressure.The system MgSO4.H20 is characterized by the occurrence of a great number of hydrates; however, above 25 ~ only MgSO4.7H20 (epsomite), MgSO4.6H20 (hexahydrite) and MgSO4.H20 (kieserite) are contained in the form of stable solid phases in aqueous solution [

The following MX · MgX2 · 6H2O compounds (double salt hexahydrates) were synthesized by variation of the M+ and X− ions: CsCl · MgCl2 · 6 H2O, Li(H2O)Cl · MgCl2 · 6H2O, NH4Br · MgBr2 · 6 H2O, RbBr · MgBr2 · 6 H2O, CsBr. MgBr2 · 6 H2O, KI · MgI2 · 6 H2O, NH4I. Mgl2 · 6 H2O and RbI · MgI2 · 6H2O. By X‐ray analysis of powder samples the lattice parameters and the space group were determined. On the basis of the results thus obtained, an identification with structural types was carried out. In accordance with the findings, the structure is made up of (M+)X6−octahedra which are linked into perovskite type units by sharing vertices. Their interstices are occupied by the Mg(H2O)62+ octahedra. A “tolerance factor” t which has been calculated on the basis of the proportion of radii and which attains values between 1.045 and 1.061 is a criterion for the upper limit of the area of existence of this structure. Carnallite has a higher to value and, therefore, a different structure.

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The effect of sodium dodecyl sulfate (SDS) on crystallization kinetics and crystal habit of MgSO, . 7 H,O from aqueous solutions at 25 "C was investigated in batch experiments. It highly depends on the supersaturation level. Both increasing supersaturation and rising concentration of the tenside promote the production of needle-like crystals but the influence of the driving force is much more pronounced. SDS increases the crystallization rate and the linear crystal growth rate in length direction of the crystals. To a high degree it also influences properties of the crystallizing solution such as surface tension and viscosity. Der EinfluI3 von Natriumdodecylsulfat (SDS) auf die Kristallisationskinetik und auf die Kristallform von MgSO, . 7 H,O wurde bei 25 "C aus wiiBrigen Losungen in Batch-Experimenten untersucht. Die Tensidwirkung hiingt in starkem MaBe vom Ubersiittigungsniveau ab. Sowohl steigende fTbersiittigung als auch Erhohung der Tensidkonzentration fordern die Entstehung nadelformiger Kristalle, wobei der TriebkrafteinfluB dominiert. SDS erhoht die Kristallisationsgeschwindigkeit und die lineare Kristallwachstumsgeschwindigkeit in Liingsrichtung der Kristalle. Es beeinfluBt auch Eigenschaften der Kristallisetionslosung wie Oberfliichenspannung und Viskositiit in starkem MaBe.JAMES, D. W., CARRICK, M. T., FROST, R . L . : J. Raman Spectrosc. 13 (19x2) 115