1朝鮮カオリン, 川俣長石, 四條畷珪石各0-100%より成る素地土19種を以て直徑10cm, 厚さ0.5-0.8cmの圓板を成形し, 之をSK 02a, 10, 12, 14に燒成して試驗片を造り, 次に熱傳導度既知の標準ガラス板と比較する拔山四郎氏の方法に據り平均温度60-70℃に於て其熱傅導度を測定した。更に此結果から氣孔率零のときの熱傳導度を計算し, SK8-14燒成物の平均値と組成との關係を求めた。
2 SK 02aで燒成した素地の熱傳導度は殆ど同一であつた。
3 SK8-14燒成物に於てもカオリン, 珪石に因る變化は殆んど認められなかつたが, 長石の増加は熱傳導度を減少せしめることを知つた。
4 陶磁器素地の熱傳導度は各原料單味の熱傳導度の範圍内に在るやうに思ふ。
終りに本研究は財團法人旭化學工業奬勵會から補助を受けた「釉に因る素地の反曲に就て」の1實驗として報告するものであつて爰に著者は同會に對して謝意を表する次第である。

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The authors continued their previous studies (This Journal, 1934, 42, 339, 471; 1935, 43. 55, 133, 263, 343) on the fine refractory and electric insulating material “steatite”, and reported the results of further comparative studies. The main points of the present communication are briefly abstracted from the original Japanese paper.
(1) Talc has the molecular formular 3MgsiO₃·H₂siO₃ (or 3MgO·4SiO₂·H₂O or H₂Mg₃Si₄O₁₂), and one molecule of silica is set free as 3MgSiO₃ SiO₂ by heating at 700-800°C. This free silica has a bad effect of unstable expansion and disintegration of the burned steatite, when the sample is applied to the hydrothermal heating under steam pressure, as already in the foregoing reports. This defect was completely excluded by adding about 5-15% of alumina in the form of aluminium hydroxide to talc powder, mixed intimately, moulded under high pressure (600kg/cm²) without water, burned at 1300-1350°C for 2 hours. The following good results were obtained by this addition of alumina.
This resuls show that the addition of about 3-15% alumina decreases the burning temperature and shrinkage, and considerably increases the bending and compressive strengths, by comparing to the results of many experiments of steatite samples moulded without alumina in the foregoing reports. These steatite samples were tested on their stabilities by the hydrothermal test in an autoclave under pressure of live steam (10kg/cm² pressure, about 180°C and 3 hours-heating), but the specimens were completely stable.
(2) Talc powder were mixed with 10-20% of Zettlitz kaolin in elutriated fine powder, dry moulded without water under pressure of 600kg/cm², burnt at 1350°C for 2 hours as before described, and then tested on various physical properties, which results are shown in the following table 2.
(3) Nextly, 5-10% of pure zinc oxide powder were mixed to talc powder, and the mixed batch powder was moulded under pressure of 600kg/cm² without water, and burnt at 1350-1400°C for 2 hours. The steatite specimens thus obtained were tested on their various properties, which are comparatively tabulated in the next table 2.
It is clearly seen from these results that the addition of kaolin gave better results than those specimens obtained by mixing with zinc oxide The steatite specimens obtained by adding 10-20% of kaolin have very large strength and very small porosity.
(3) These three sorts of steatite samples i e., (a) mixed by alumina (b) mixed by kaolin and (c) mixed by zinc oxide, were compared on their spalling properties by quick cooling or quenching in water. The method was modified by the present author (S. Nagai), carried out as following: small cylindrical (dia. 2cm and length 2.5cm) test pieces were heated at 800°C or 1000°C for 30 minutes in an electric furnace, colled or quenched by quick dropping into large volume of cold water, dried, and then determined their densities and compressive strengths. This quick cooling or quenching was repeated 2 or 3 times and the degree of decrease of strength was compared, as shown in the following table 3.
As seetn from these results it is easily seen that the steatite from talc and alumina has the largest resistibility to quick cooling or quenching, that from talc and kaolin is of the second quality, and that from talc and zinc oxide decreases considerably its strength to one thirds of the original strength by one quenching.
(4) The stability test, by heating the steatite specimens in superheated live steam of high pressure (10 atmospheric pressures and about 180°C in an autoclave) for 3 hours, gave the clear result, that (a) steatite from talc and alumina as type Al-3-Al-11 was completely stable, (b) steatite from talc and kaolin as typeK-1-K-4 was

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