We observed that quick lime containing gypsum had the property of hardening under water, but it sets very fast and evolves heat as a result of the hydration of quick lime and reaches about 70°C. So, we prepared the plasters which contained gypsum and several substances such as retarding the hydration of quick lime and measured the temperature in the process of setting and the strengths of the hydrates. In addition to the above experiments, we determined the solubility of CaO and SO₃ and identified solid phases by X-ray diffraction in the process of the hydration of quick lime in order to clear the reason of the property of hardening. A summary of the results of these experiments is given under.
(1) The prepared plasters have about 50 kg/cm² in bending strength and 200 kg/cm² in ocmpressive strength in a day.
(2) The evolution of heat can be fairly reduced and the setting time can be controlled by the addition of glycerine, diatomaceous earth and Portland cement clinker.
(3) The strengths of the plaster reduces little by the addition of retarders.
(4) The solubility of Ca (OH) ₂ is lowered by the addition of gypsum in the process of the hydration of quick lime. The more higher the temperature due to the heat of hydration, the more lowered the solubility.
(5) The addition of gypsum does not form new compounds but makes large the sizes of the crystals of slaked lime.

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Growth of calcium oxide crystals was attempted by decomposing calcium carbonate in molten sodium chloride which has been heated to a constant temperature of 950°C.
The mixing ratio of sodium chloride and calcium carbonate has a marked effect on the shape of grown calcium oxide. That is, if the experimental condition and operation are suitable, it can be grown into fibrous crystals which attain a diameter of 2-3 μ and length of 0. 5-1. 0 mm with CaCO₃/NaCl ratio of 0.5/10-3.0/10, a plate form whose one side is 0. 5-1. 0 mm with CaCO₃/NaCl ratio of 0. 3/10-0. 5/10 or large calcium oxide crystals in the shape of octahedron.
Also, the crystalline shape of calcium oxide with passage of time in molten sodium chloride has the tendency of changing gradually from the needle shape to octahedron shape. Generally the speed of crystal growth is fast in this case and the growth calcium oxide indicates a skeleton crystal state.
Even when limestone rock is used, the crystal growth will be almost the same as in the case of precipitated calcium carbonate, if ground finely.
It was confirmed from X-ray diffraction also that the crystals which grew as mentioned above were calcium oxide crystals.
There is almost no crystal growth when calcium oxide which was formed by calcining calcium carbonate beforehand was used as the sample.
It was inferred from the above that the mechanism of crystal growth of calcium oxide takes place in the sequence of calcium carbonate sample first dissolving in molten sodium chloride, liberating carbon dioxide from calcium carbonate and then formation of calcium oxide nuclei and crystal growth taking place.

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Selection of phosphate rocks as the raw materials for the industries is highly important.
The writer presented the following four values of phosphate rocks. These values revealed certain relations between apatites and calcite, between fluorapatites and other apatites, and among main components in matrix. He showed a classification of the rocks based on those values (Fig. 2) is more reasonable and convenient than that of (Fig. 1)
1) “R-value” ¹⁾ referred to T-CaO/T-P₂O₅ mol. ratio, and it showed 3.00 in tricalcium phosphate Ca₃ (PO₄) ₂, 3. 32 in apatites Ca₁₀ (PO₄) 6x 2 : 3.2-5.0 in phosphate rocks. The last values showed great deviation from the theoretical value (apatite=3.32) which may suggest the phosphate rocks contain “Excess-lime” (Table 1 and Fig. 2)
2) “Excess-lime value” ²⁾ was calculated as follows, Excess-lime value=T-CaO wt %-T-P₂O₅ wt % x 1.315 CaO% to be included in apatites This value represented by CaO wt %, and suggested possible maximum quantity of any calcium salts (commonly calcite) in the phosphate rocks. (Table 1)
3) “F-value” ³⁾ referred to the fluorine content in apatites, expressed as T-F2/T-P₂O₅ wt % raito. The value revealed the mixcrystal state fluorapatites Ca₁₀ (PO₄) ₆F₂ and apatite excess in fluorine Ca₁₀ (PO₄) ₆F₃, nonfluorineapatites : Ca₁₀ (PO₄) ₆ (OH) ₂ and Ca₁₀ (PO₄) ₆CO₃ those present commonly as indeterminable microcrystals in the rocks. (Table 2 and Fig. 2)
4) “Matrix value” ⁴⁾ referred to the ratio of main components which comprise matrix present in phosphate rocks, namely, CaO as “Excess-lime” : R₂O₃ : SiO₂=X : Y : Z considering from difference of the “Matrix value” the rocks were classified into three groups (Fig. 4 in the previous report⁴⁾). All of the values above mentioned may be easily calculated from chemical analysis without optical or X-rey studies, and may contribute to the reasonable raw material choice and process control in relating industry. (Table 3)

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