Fundamental studies were made to produce calcium chromates from chrome ore to be used for the refining of chromium alloy. By calcination of chrome ore (Cr₂O₃ 55.0%, FeO and Fe₂O₃ 13.6%, MgO 15.9%, Al₂O₃ 7.3%, SiO₂ 4.0%) with lime, Ca₃(CrO₄)₂ (β-tricalcium phosphate type) was formed above 850°C with the increase in weight due to the oxidation of Cr³⁺ to Cr⁵⁺.
6CaO⋅nAl₂O₃⋅3-nFe₂O₃ and MgO were also formed as are shown in Table 1.
By heating pure Cr₂O₃ with CaO various calcium chromates were formed (Table 1). From chrome ore, however, Ca₃(CrO₄)₂ was the only chromate formed except slight amount of Ca₇Cr₄O₁₇ which was formed when a large amount of CaO was blended.
Nearly 90% of Cr of the ore present as Cr³⁺ was oxidized to Cr⁵⁺ when very finely powdered chrome ore (-200mesh) was blended with suitable amount of limestone (100:140 by weight, CaO/Cr₂O₃ mol ratio 3.9) and was heated for more than two hours in air at 1000°-1300°C (Fig. 3). The oxidation ratio (Cr⁵⁺ per cent of total Cr of the calcined product) was smaller when coaser raw materials were used (Fig. 4).
It was found that the addition of small amount of fluorspar (CaF₂) promoted the oxidation remarkably resulting in the formation of a compound Ca₅F(CrO₄)₃ (fluorapatite type calcium chromate, Table 2). Calcined in the combustion gas containing small amount of O₂, the oxidation ratio of the chrome ore blended with imestone without fluorspar was very small. Addition of fluorspar raised remarkably the oxidation ratio in this case, too (Fig. 8).
It was also found that the calcined product containing Ca₅F(CrO₄)₃ was very useful as the additive agent to high carbon ferro-chromium to depress the carbon content.

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“SHIRASU” is distributed chiefly in southern Kyushu and consists of volcanic ash, pumice and other materials. SHIRASU and coral limestone were used as raw materials of autoclave-hardened bodies. The press molded and then autoclaved bodies were prepared as follow; mixing ratio of SHIRASU: coral limestone=1:1, 3:1, 6:1, mixing water 15%, press-molding pressure 200kg/cm², curing pressure 5-15kg/cm², curing time 4-16hrs. Results are as follows; apparent density 1.81-1.93, bulk density 1.41-1.54, water absorption 21-29%, compressive strength 46-505kg/cm².
The porous lightweight autoclaved bodies were prepared as follow; mixing ratio of SHIRASU: coral limestone=1:1, 2:1, 4:1, mixing water 54-90%, Al powder 0.05-0.75%, curing pressure 10kg/cm², curing time 10-40hrs. Results are as follow; apparent density 1.05-2.54, bulk density 0.48-0.90, apparent porosity 51-86%, compressive strength 4-85kg/cm².

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It is well known that Pyrex glass, borosilicate glass with high silica-content, is more difficult to be melted homogeneously than other glasses, because striae, knots, and stones very often arise during melting. It is the purpose to confirm the cause of striae, knots, and stones arising during melting in commercial Pyrex glass wares. Experimental equipments used, are centrifuge, interferometer, and strain analyzer.
Most of striae have lower refractive index. They arise from raw material difficult to melt, SiO₂, at early stage. At later stage they mainly arise from surface volatilization. The striae with higher refractive index arise from Al₂O₃, ZrO₂ exuded by refractory corrosion, and also stagnants which originate from refractory corrosion have higher refractive index.
The knots occur mainly from segregation of silica sands in raw materials and the refractive index is lower. But the knots with higher refractive index can be seen occasionally. They arise in the melting process of stones from refractories.
The stones almost arise from segregation of silica sands in raw materials as well as knots. The refractive index of the surrounding glass is lower than that of the parent glass. The stones with higher refractive index originate from refractories.

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We have already studied the condition of glass-formation and the glass-formation range of borates, silicates and germanates. In these studies, however, we could not determine precisely the cooling condition which defines the glass-formation range, because the glassy stateis not a stable state, but a sub-stable one. These experiments were made under conditions which were determined for the sake of experimental convenience: namely, 1/80mols of specimen were melted and cooled naturally in a room. Therefore, it is necessary to examine to what extent the results of these experiments are effective in view of the glass structure. In this study experiments were carried out by changing the cooling rate, and the variation in the glass-formation range with various cooling rates was examined. These cooling processes included the followings: quick cooling by water, natural cooling in a room (cf. Curve I in Fig. 1), natural cooling in a furnace (cf. Curve II in Fig. 2) and slow cooling in a furnace controlled by a thermocontroller. These cooling rates are about 3×10², 10, 1.5×10^-1 and 1.2×10^-3°C/sec, respectively. The amount of molten glass is the same as that in the previous studies; crucibles employed are made of platinum or its alloy, which may have some effect especially in the case of the slow cooling in a furnace.
Ternary borate systems have been chosen as the glass-forming system for the convenience of experiment, which have been divided into common systems and exceptional systems. The former include the B-type ternary system as the containing only the oxides of the a-group elements, the PbO-containing ternary system as the one containing both of the oxides of the a-group and the b-group elements, and the B₂O₃-Bi₂O₃-PbO system as the one containing only the oxides of the b-group elements. The results are shown in Fig. 1-19. These glass-formation ranges contain various critical lines of vitrification; the limit of the continuity of a network-structure (the AD-line in Fig. 2 and 3), the existing limit of necessary modifier ions for the network-formation (the B₂O₃-C line in Fig. 2 and 3), and the exchangeable limit of network ions represented by the number of b-group ions connecting B with B in the network-structure (the A₁B₂, A₂B₃, … lines in Fig. 8; cf. Table 1). The glass-formation range expressed by the above critical lines generally varies somewhat according to the variation in the cooling rate. Therefore the result of the glass-formation range under an arbitrary cooling condition has no absolute meaning. However, comparing Fig. 4 with Fig. 5, for example, we can see a similar variation in the glass-formation range in both cases. In the one case the modifier ions are not exchanged but the cooling conditions are changed, while in the other the modifier ions are exchanged but the cooling conditions are kept constant. This fact can be explained by assuming the 3-dimensional glass-formation range including the glass stability as shown in Fig. 7. When the modifier ion in the B₂O₃-PbO-RO system (Fig. 5) is smaller, so that its vitrified system is more unstable, the glass-formation occurs only in the high stability sections. The case is the same when the cooling rate is slower in a more stable vitrified system.
We then studied the B₂O₃-MgO-BaO system (Fig. 9), the B₂O₃-TiO₂-BaO system (Fig. 12), the B₂O₃-WO₃-Li₂O systems (Fig. 15) and the B₂O₃-K₂O-Bi₂O₃ system (Fig. 17) as exceptional ternary systems and discussed the true feature of the anomaly of these systems. In the

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