The reaction products obtained by exposing the magnesium hydroxide powders dampened with moisture to CO₂ gas were investigated in their individual process conditions and the exothermic phenomenon at approximately 500°C in the D. T. A. curve of the basic magnesium carbonate was studied.
(1) When the condition was 70°C and RH 100%, the reaction product was completely carbonated after about 24 hrs and the chemical composition of that was 5 MgO·4CO₂· 6.9-7.0H₂O, but in the case of 30°C and RH 100%, the unreacted magnesium hydroxide was observed even after 72 hrs.
The X-ray diffraction pattern of the reaction product was similar to that of the basic magnesium carbonate, but the diffraction 002 shifted remarkably to a small angle.
(2) Since the exothermic phenomenon at approximately 500°C in the D. T. A. curve was recognized only under the condition of which MgCO₃ is formed on the thermal decomposition, it was estimated to be closely related to the MgCO₃ formation.

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The present investigation has been carried out in order to find the significant factors or characteristics for improvement of water resistance of set gypsum. Asphalt-Wax emulsion (emulsified by cationic surface active agent in Hurrel Homogenizer) was employed as the water resistant material. Bulk density, porosity, setting time, compressive strength and water absorption of specimens admixed this water resistant material were determined and the correlation between these physical properties and the factors such as addition amount of Asphalt-Wax emulsion, water/plaster ratio, penetration of asphalt used, Wax/Asphalt ratio in the emulsion and addition of potassium sulfate was discussed.
The results are summarized as follows;
(1) The mixture of asphalt and wax has the synergistic effect on the improvement of water resistance of set gypsum, showing maximum effect when Wax/Asphalt ratio was 30% in the present experiment. (2) The results of analysis of variance executed to estimate the factor effect on water resistance showed that the Wax/Asphalt ratio in the emulsion was the most effective factor and in sequence, addition amount of K₂SO₄ and addition amount of the emulsion were effective. (3) Bulk density and porosity of set mass and setting time are not in substantial conjunction with water absorption, but predominated by the effectiveness of water resistant materials admixed. (4) For all factors except water/plaster ratio, under the more effective condition to improve water resistance of set gypsum, the more decrease in compressive strength was observed.

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Studies were made on the formation of calcium carbonate in the manufacture of nitric phosphate by PEC process and on the change of products during storage.
Ammonia and carbon dioxide were introduced to the slurry obtained by the decomposition of phosphate ore (added 0.05 mole MgO for 1 mole CaO) with nitric acid (45% HNO₃).
The formation of calcium carbonate depended on the pH of slurry. Above pH 7, calcium carbonate was found in the producted slurry. Fluorapatite was formed in the slurry, but was not formed in the dried product of the slurry during storage.

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