A Korean kaolin, a Kawamata feldspar, a Shijonawata quartz, and a porcelain body were heated at temperatures varying from 600°C to 1300°C, every 100°C, for 2 hours. The products were examined for the solubility in 20% hydrochloric acid at 100°C. On the other hand, pyrometric cone equivalents were determined for the ternary system kaolin-feldspar-quartz up to cone 19. The melted-down and glassified cones made from 15 mixtures among 24 were tested similarly for the acid-resistibility.
The results of the investigation seem to justify the following conclusions:
1. The acid-resistibility of the heated kaolin changes distinctly at those heating temperatures where marked changes occur in its thermal reaction, microstrueture, and thermal expansion. Neither the feldspar nor the quartz undergo any noticeable change in their acid-resistibility by a previous heating. On heating at temperatures between 600°C and 1000°C, the porcelain body shows about mean solubility of the three raw materials, and the relations between the solubility and the heating effects is not so distinct as in the kaolin. After heating the kaolin, feldspar, quartz, and porcelain body at 1100°C or 1200°C, there are only slight differences among their solubilities.
2. When the quartz is dissolved in the feldspar, an increase in the quartz causes almost no change in the acid-resistibility of the glasses, while their refractoriness is raised evidently.
3. When the kaolin is dissolved in the feldspar, both of the acid-rebistisility and refractoriness are raised with the increating kaolin.
4. When the quartz and kaolin are dissolved in the feldspar at the asme time, the acid-resistibility of the products is raised markedly with an increase in the kaolin, and is probably favored a littele by an increase in the quartz.

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The authors, continuing the previous studies (This Journal, 1934, 42, 339, 471; 1935, 43, 55, 133, 263) on the fine refractory and electric insulating material “steatite”, reported the results of further comparative studies. In the following, the main points of the present communication are briefly abstracted from the original Japanese paper.
(1) Several steatite specimens were stored for 3 months, after burning, in the air of the laboratory. All samples were seen expanded, especially the samples burned from talc only or with small addition of boric acid considerably expanded. The authors assumed that this expansion was owing to the moisture and carbon dioxide in the air.
(2) To ascertain this expansion, 4 sorts of samples were put on to the hydrothermal treatment by heating in the autoclave of superheated steam of 10 atmospheric pressures and ca. 180°C for 3 hours. The samples No. 3 (talc only) and No. 4 (talc with 3% boric acid) disintegrated considerably, No. 2 (talc with 0.6% magnesium chloride) expanded, but No. 1 (talc with 3% alumina) was seen completely stable and in constant dimensions. So that, the reason of expansion was, as assumed above, clearly owing to the combination of water with the free silica of cristoballite form in the heat decomposed talc molecule, which is produced by calcining or burning talc (H₂Mg₃ Si₄O₁₂ or 3MgSiO₃·H₂SiO₃) to anhydrous matter Mg₃Si₄O₁₁ or 3MgSiO₃·SiO₂. This combination of water molecule with silica in the calcined talc and returning to talc molecule was accelerated by the hydrothermal treatment of superheated steam under high pressure, as above treated.
(3) The modified spalling test or quick cooling test was applied to the steatite specimens of various burning conditions obtained in the foregoing experiments. The spalling test was modified by one of the present authors (S. Nagai) and carried on, as follows: the small cylindrical test pieces (dia. 2cm and height 2cm) were heated at 800, 1000, 1200 or 1300C for 30 minutes and quickly dropped in the water. The compressive strength and other physical properties were compared with those before this heat treatment, and the decrease of strength were principally discussed. The second modified test was also carried on, as follows: the test pieces applied to the repetitions of the heating at 800 or 1000°C for 30 minutes and then dropping quickly into water 2 or 3 times until to the complete disintegration of the test pieces, and the decrease of strength was principally compared. In the following tables are compared the results of these spalling or heat treatment tests, by using several steatite samples from talc, “Shuganseki”, etc.
As seen from these results, the modified spalling test is suitably applicable to compare the resistibility of steatite to the quenching. The quenching temperature must be selected, (1) 1000°C or 12000°C for the test of comparing the decrease of strength over 50% by one quenching and (2) 800°C for repeated spalling test.
(4) The authors will report in their next communication several further results of studies, (1) the special steatite obtained by mixing small quantity of alumina, zinc oxide, chrome oxide, etc., (2) expansion tests of various steatite specimens, (3) electric properties, etc.

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1. There is no correct method of the surface temperature measurement yet, as it is very difficult.
2. Author propose of two new “Elongation Method” and “Surface Temperature Scale Method”, both contrived by himself.

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[in Japanese]

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