The principal purpose of this investigation was to make clear the oxidation behavior at 1200° to 1400°C of silicon carbide bodies containing 15% bonds in the system K₂O-Al₂O₃-SiO₂.
The oxidation resistance was determined using a small plate specimen 14mm in diameter and about 8mm thick. For most of work the specimen was oxidized at 1200° and 1400°C in a flowing atmosphere with controlled amounts of oxygen and water vapor. The weight gain, volume change, and porosity of the specimen were determined. The results obtained are summarized as follows:
(1) The bonds containing large amounts of K₂O and Al₂O₃ retarded the oxidation of silicon carbide. At 1200°C K₂O was more effective on reduction of the oxidation than Al₂O₃, but at 1400°C the effect of Al₂O₃ on the oxidation resistance became somewhat high.
(2) Silicon carbide was oxidized very strongly by the mixture of water vapor and oxygen when heated above 1200°C. It was observed that at such a high temperature the specimen swelled and cracked and permitted oxidation.
(3) The presence of Al₂O₃, K₂O in the bodies and water vapor in the atmosphere caused the formation of cracks, which had also been found in ceramic bonded silicon carbid refractories. The mechanism of formation of cracks was explained on the basis of reactions in the system K₂O-Al₂O₃-SiO₂-H₂O.
(4) After heating the specimen in air at 1400°C for 10 hrs the rate of oxidation by water vapor at 1200°C diminished considerably.

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Commercially, it is difficult to fabricate reproducible pieces of BaTiO₃ ceramics having the same coluor and the same electrical properties, because these properties are strongly influenced by the presence of pentavalent ions such as Nb⁵⁺, Sb⁵⁺, Ta⁵⁺, V⁵⁺, etc. which might possibly come as impurities from TiO₂, one of the raw materials of the ceramics.
In the present work were established experimentally the effects of the additional agents of pentavalent ions on the colour and the electrical properties of BaTiO₃ ceramics.
The results obtained may be summarized as follows: (1) The addition of Sb⁵⁺, Ta⁵⁺, and Nb⁵⁺ ions respectively, caused a great change in colour of the fired specimen; in all cases the colour changed from light brown to light green and then to bluish grey at their oxide content of 0.10% and 0.20%. (2) The addition of Sb⁵⁺ and Ta⁵⁺ respectively caused a great decrease in a specific electric resistance of the specimen whereas that of V⁵⁺ exerted only a small influence. The specimen added with Sb⁵⁺ and Nb⁵⁺ respectively showed an abnormal polarization phenomenon. The changes in properties for the BaTiO₃ ceramics were explained by Weyl's concept (Ind. and Eng. Chem., 42 [2] 255, 1950) which was originally developed for the explanation of the change of TiO₂ in the colour and specific electric resistance.

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An opal type of photosensitive glass, when exposed to ultraviolet light and subsequently heated to about its softening temperature, changes in transparency due to the formation of nonmetallic submicroscopic crystallites within the glass. In this study the transparency change of the glass having the following composition was studied in relation to the exposure time: SiO₂ 81, Li₂O 12.5, K₂O 2.5, Al₂O₃ 4, CeO₂ 0.03, Au 0.027% by weight.
Glass specimens of 2mm thick plates were exposed to ultraviolet light by placing the near a 500 watt high pressure mercury lamp at a distance of 10cm for various times ranging from 1 to 1000 min. After exposure all of specimens were heated firstly at 510°C for 30 min. and then at 620°C for 60 min. to cause the formation of gold nuclei and lithium metasilicate crystallites at respective temperatures. The measuremeat of light transmittance in the visible region was made of these specimens with a photoelectric spectrophotometer.
It was found that (1) the transparency decreases with increasing exposure time up to 30 min. (due to the formation of metasilicate crystallites); (2) between 30 and 180 min., however, it increases with increasing exposure time; the specimen with the exposure time of 180 min. is almost transparent though its color is deep red; (3) over 180 min. it again decreases with increasing exposure time.
The peculiar change in transparency with increasing exposure time was discussed on the basis of the size of lithium metasilicate crystallites within the glass. The increase in transparency with increasing exposure time in the range between 30 and 180 min, was attributed to the decrease of the size of crystallites under a limiting value which is too small for scattering visible light within the glass. The density measurement by a sink-float method was also made to support this conclusion.

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In the previous paper (J. Ceram. Assoc. Japan, 66 [10] 233 (1958)) was reported the mechanism of the chemical attack of gasses and liquids on the surface of some heavy crown glasses. This paper describes the same kind of investigation on some flint glasses. Six kinds of flint glasses having different chemical compositions (see Table 1) were subjected to the attack of gasses or liquids, and the resulting change of their surfaces were examined by the same method as used in the previous work.
The way in the change of the surface structure by the chemical attack was different depending on the chemical compositions of the glass: For the glasses of low SiO₂ and of high PbO or high BaO content (C, D, G, H, glass in Table 1), the attack of gasses resulted in the formation of salts of heavy metals on the glass surface which appeared as the frost. Directly under the layer of this salt there existed another thin layer having the structure of α-quartz, which appeared as the stain after the salt layer was removed. The attack of liquids caused the formation of a SiO₂-rich film on the glass surface as the result of leaching out of the metallic ions from the inner part of the glasses. For the glasses of high content of both SiO₂ and alkali oxide (E, F glass in Table 1) the condensation of water vapour occured at the glass surface much easier than in the above glasses. When the glasses were subjected to the attack of CO₂ gas containing water vapour, the layer of carbonates was formed on the glass surface, which appeared as the frost. After the carbonate layer was removed, however, no stain was observed. The attack of liquids also did not cause the formation of the stain The fact that the stain was unable to observe for this class of gasses was explained by the small difference in optical indices between the glass itself and the thin SiO₂-rich film formed.

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Methods for the determination of Fe₂O₃, Al₂O₃, CaO and MgO in magnesia clinkers are described. The speed of determination of these constituents has been greatly increased by the use of ethylenediaminetetra-acetic acid (E. D. T. A.) because all separations have been eliminated. The results obtained are shown in Table 3 and 4 together with the gravimetric results. It is seen that the accuracy and reproducibility of the E. D. T. A. method are satisfactory.

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