The fertility of sloping salt field was defined to the ability of brine production in some value of Shijoka area ratio. Geographical and climatic conditions, construction of salt field and Shijoka; and human faculties were the factors of field fertility, and they influenecd to each other. Therefor, it was dificult to distinguish each influence. In this paper, the field fertility was described with the actual results in salt field and culculations in some assumptions.

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Unsaturated polyester resin are cured easily under room temperature and contact pressure, investigating for the purpose utilize to the protective coating of surfaces of metals, wood and cementmortar in the salt manufacturing, were found full well reinforcing effect by using carbon powder as the filler for relary of the glass fiber reinforcing method. From the results of various tests were certificated to be reformed remarkably the resistance of sea water brine, thermoresistance, anti-exposed and adherent property, etc.. by addition of carbon powder.

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In the concentration process of sea water at 25° and 110°C, then composition of the solutions, and the amount of evaporated water and of solid salts were calculated by means of the determinant method. This method makes it possible,1) easily to calculate more than three dimensional system, but the graphical method was limited within not more than three dimensional system, 2) to get the results in any precision. And 3) however, it takes much time for calculation. Rectangular-triangle system was adopted. It is superior to regular-triangle system in using ordinary section-paper. The latter requires special section-paper, 120°. To avoid unnecessary steps of calculation, this method was applied to the ionic system Na⁺-Mg⁺⁺-Cl^--SO₄^-- instead of the system NaCl-MgCl₂-MgCl₂-MgSO₄-KCl. Treatment of the plane-containing more than three points was discussed. Such three points must be selected, as the plane made by these three points has minimum solubility.

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Common calcium superphosphate is inferior to fused phosphatic fertilizer, which is manufactured from rock phosphate and serpentine and contains P₂O₅ about 20-22%, SiO₂ about 22-25 %, CaO about 25-30 %, and MgO about 16-20%, owing to no content of magnesia.
In the present study, magnesian calcium superphosphate fertilizer was prepared by mixing superphosphate with various magnesia containing materials, i.e., serpentine, dolomite or sea-water magnesia, and these special magnesian calcium superphosphate samples ware compared on main compositions, especially the changes of solubilities of P₂O₅ and MgO in 2% citric acid or 0.5 NHCl solution by storing 1, 4, 8 or 12 weeks.

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