Action of various electrolytes of sulphate salts on anhydrous gypsum plaster was systematically investigated. Powder of natural and reclaimed crystal gypsum was calcined at 400, 500, 700, and 1000°C for 1 hour, and kneaded with 1% solution of various sulphates of 1-3 valency metal, e.g., simple salt Na₂SO₄, ZnSO₄, Al₂(SO₄)₃, mixture of these two or three salts of K-, NH₄-, Fe-, Al-alum. From many results of comparative tests. Al₂(SO₄)₃, ZnSO₄ and K-Al-alum or Fe-NH₄- alum were observed to be better addition agent than other salts, for the properties of compressive strength, hardness, etc. of hardened anhydrous gypsum plaster. Na₂SO₄ was observed to be un suitable agent by the bad effect of efflorescence in any case of simple or mixed use with other sulphate. The addition of hard soluble CaO or CaSO₄. 2H₂O was also to be undesirable admixture. and the effect of CaSO₄. 1/2H₂O addition agent is now being studied, which result will be hereafter reported in the following report.

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The corrosion tests of the special dolomite refractories against fused phosphate fertilizer (C. P. 20%) were made by the crucible method and fusion test of mixed cone. The crucibles have an inside diameter of 20mm, depth of 15mm and wall thickness of 5mm., were kept filled with fertilizer at 1400°C for 20 minutes, 1500°C for 2 hours and 1600-1640°C for I hour on the test run No. 1, 2 and 3 respectively.
The thickness of the corrosion layers at flux line. were about 0.1, 0.7 and 2mm respectively. The penetration of the melt through the crucible walls of 5mm thickness were not observed in every cases. The results of the tests of mixed fusion were shown in Fig. 1.
The results of these corrosion tests of the special dolomite refractories showed that these cheap and durable basic refractories have the possibility to be used as a furnace lining for manufacture of fused phosphate fertilizer.

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In continuing the previous reports (I and II), various different points of properties between specially sintesed alumina cement and ordinary fused product, which were produced from alumina residue obtained as byproduct from aluminium metal reclaiming plant and slaked lime with small addition of bauxite, aluminoms shale or pyrite cinder, were fully compared on heir chemical compositions, physical properties, strengths of 1:2-plastic mortar at 3, 7 and 28 water curing days. The special alumina cement, which was reported by the present authors to be produced by the special sintering process in the foregoing reports, contained small amount (about 2-5%) of free lime, which gave effect on setting time of the cement, and also contained small amount (3-5%) of insoluble or inactive residue of α-alumina of corundum type, which was introduced from the raw material of the alumina residue as bypsoduct of aluminium reclaiming or remelting plant. These incompletely combined components could be diminished by adding very small amount (0.5-1%) of calcium fluoride (CaF₂) or fluorspar at the sintering the raw mixture at about 1300-1350°C. Nextly, three samples of (1) raw material of alumina residue, (2) sintered alumina cement and (3) fused alumina cements were tested by the differential thermal analysis and observed, on the curves of the thermal analyses, several turning points owing to the free lime and free corundum alumina contained in the (1) alumina residue and (2) sintered alumina cement.

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