The mechanism of hydration of quick lime was investigated by the determination of solubility of quick lime in liquid phase in accordance with JIS R9011-1964 method of chemical analysis of lime.
From test results the following was obtained.
(1) The solubility of quick lime or hydrated lime is in inverse proportion to temperature, decreasing as temperature rises.
(2) The magnitude of solubility of quick lime in liquid phase is supersaturation at different tem-peratures. On the other hand, the magnitude of solubility of hydrated lime in liquid phase is not supersaturation at different temperatures.
(3) The solubility of quick lime mixed with sodium fluosilicate is smaller than that of quick lime.
(4) The solubility of hydrated lime mixed with sodium fluosilicate is smaller than that of hydrated lime.
(5) The difference of solubility of quick lime from solubility of hydrated lime is smaller than the difference in solubility between quick and hydrated lime mixed with sodium fluosilicate.

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Previously many studies on the crystal hadit modification of gypsum byproduced from wet phosphoric acid process by reaction conditions and by the modifiers were reported.
In the present paper, we have researched statistically the crystal habit modification effects of the material of reaction vessel. Four reaction vessels which materials are respectively lead, polyethylene, stainless steel, glass were used. In these vessels a cosia phosphate rock of Table I was decomposed by sulfuric acid under various conditions which are shown in Table II. After seed crystals were added to the resultant slurries, the crystallization of the gypsum were accomplished. By microscope, 20 crystals which were selected at randum from grown gypsum crystals and were measured of its length L (μ) and width W (μ). The crystal form was indicated by the form parameter of mean L/W value and the crystal size by mean √LW value of the 20 crystals. The modifying effects were analysed statistically by these parameters and were obtained following results. On the case of grown crystals from the both seed crystal nucleated and added, the materials influence significantly on the crystal size and on the crystal form.
Another case of the grown crystal from the added seed only, the metarials has none influences on the crystal size and crystal form.
We recognize the reasons of these influences of the material of the reaction vessel on the crystal growth of phosphoric acid gypsum, are the modifying effects of ions which were produced by corrosion of the lead, stainless steel and probably glass. We intend to discuss these reasons more accurately in the next papers.

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