Magnesium bis (hydrogenphosphoramidate) tetrahydrate was made by adding an aqueous magnesium chloride solution to an aqueous potassium hydrogenphosphoramidate solution cooled below 5°C. The product was stable at 4°C, but decomposed slowly to form polyphosphates at 30°C. The phosphoramidate was converted to crystalline magnesium metaphosphate by heating above 650°C. According to the study of the isothermal decomposition of the phosphoramidate at 150°C, no formation of P-NH-P linkages by the elimination of NH₃ from P-NH₂ linkages was observed. It was concluded that the phosphoramidate thermally decomposed to form only polyphosphates in air, and bound water seemed to play an important role in the decomposition. A mechanism of thermal decomposition of the phosphoramidate has been proposed on the basis of the formation of a zwitter ion as follows : O=p-O HO-P-NH₂ Mg1/2→O=P-P -O-P-NH₃+ Mg1/2

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The metastability of α-CaSO₄.1 /2H₂O in 20-40% H₂SO₄ solutions was studied by wet DTA method. The solid phase formed was examined in terms of combined and hydration water and by x-ray diffraction analysis.
On the basis of the measured values of reaction temperature and induction period for hydration of α-CaSO₄.1 /2H₂O in 20-40% H₂SO₄, , solutions, the relation between three factors of H₂SO₄ concentration z (6/9), reaction temperature y (°C) and induction period x (min) were given as follows : y= (-0. 5179e^0.1163z + 86. 81) x (8^{.981-×10-19 z10.60+ 0.01627}) (where z=20-40 and x=1-30)
From above and previous results¹⁾, it was confirmed that the metastable zone for both a-CaSO₄. 1/2H₂O and CaSO₄.2H₂O in 20-40% H₂SO₄ solutions existed in the range of temperature from 81.5 to 98.5°C in 20% H₂SO₄, 69. 8 to 90. 1°C in 30%, 56.5 to 84.2°C in 35% and 32.5 to 76. 7°C in 40 %, respectively.
From the results of composition analysis of solid phase formed, it was confirmed that a-CaSO₄. 1/211₂0 converted to CaSO₄.2H₂0 and 11 CaSO₄ by simultaneous reaction in 20-40% H₂SO₄ solutions.

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The ground gypsum dihydrate (the ground) has powerful accelerating effect to the setting of gypsum hemihydrate (hemihydrate), and it is increased by cooperation with usual accelerators, and the setting can be shortened to 20-90%.
The ground deducts the retarding effect of usual retarders, and shortenes the setting time to 20-70%.
Set gypsum mixed with the ground has higher compressive strength than normal set gypsum.
By scanning electron micrograph of the ground crystal which was taken from the slurry under setting, the activated nucleation on the crystal surface was observed.
The ground loses water of about 0. 7% by atomospheric drying or by coevaporation with ethanol. Quantity of this loss was calculated from the increase of crystal surface, and was nearly equal to experimental value.
The dehydration of the ground begins at about 60°C, and the activation energy of this dehydration was estimated as 250 J/mol. Uuder atomosphere of RH 81% and room temperature the ground loses water of about 0. 7%, and then absorbs moisture to 0.4% increase of the weight. Under this condition mixture of hemihydrate and the ground absorbs moisture quickly and converts to dihydrate.
Under RH 9% and room temperature the ground acts as under RH 81%, but the mixture of hemihydrate loses water of about 0. 7% and then absorbs moisture to 0. 4% loss of the weight regardless of the coexistence of the ground.
The mechanism of this moisture absorption can be explained that the ground carry the water to hemihydrate from moisture by repeating dehydration and absorption.

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