In order to study the mode of development of needle crystals in the feldspar grains composing porcelain bodies, 10 (weight)% coarse potash or soda feldspar grains were mixed with 90% kaolinite or halloysite bodies and fired. Thin sections of the fired bodies were microscopically observed with following results.
(1) The temperatures at which needle crystals start to deposite within the feldspathic glass grains, are lower in the potash feldspar grains than in the soda ones, in the kaolinite bodies than in the halloysite ones, and furthermore, in the case of the slower heating rate than in the case of the faster (Table 2).
(2) In the potash feldspar grains, the needles are initially deposited at boundary parts with kaolinitic matrix and orientated normally to the boundary face. While, in the soda feldspar grains, the crystals are, from the earliest stage, deposited not only in the boundary parts, but also within the inner parts of the grains. The needles are scarcely normally orientated in the latter case.
(3) The needles grow with firing temperatures and holding time. Generally, they are longer in the soda feldspar grains than in the potash ones, and also in the kaolinite bodies than in the halloysite ones (Figs. 1 & 3).
(4) The amounts of the crystals are also increased with firing temperatures and holding time. Commonly, the crystals are more abundantly formed in the potash feldspar grains than in the soda ones, and also in the kaolinite bodies than in the halloysite ones (Figs. 2 & 4).
(5) It seems that diffusion of some components from the kaolinitic matrix is indispensable for the deposition of the needle crystals within the grains. The diffusion may have taken place through comparatively long distance within the kaolinitic matrix. This is inferred from the fact that the crystal growth in a feldspar grain is markedly decreased if it is located close to another grains.
(6) The crystals are grown either from the grains of decomposed clay minerals coming in contact with the feldspar glass, or from the crystalline kern formed within the melt. The former occurs when the diffusion is rather slow, thus resulting in a high concentration gradient, while the latter occures in the reversed case.
(7) The mechanism of the formation of the needle crystals may, principally, be similar for potash and soda feldspars, but, usually a remarkable difference is observed between the aspects of their crystal growth. The difference seems to be due to differences between the properties of their melts, especially viscosity.
(8) From the environment of their formation, as well as from their optical properties observed, the needle crystals are to be inferred as mullite.

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Contractions or density changes of chilled lead glass samples caused by heating them at constant temperatures in the temperature range from 150° to 500°C, were observed by both interferometric dilatometer and sink-float method for measuring density. By comparing the time-contraction relations at various temperatures with the equations proposed by Tool, Ritland or Kanai and Sato, it was found that these equations did not hold exactly in the abovementioned temperature range which is lower than that examined by the above authors. It was supposed that there must be several mechanisms which cause this density change, and the mechanism which contributes mainly to the density change must be different for different range of temperatures.

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小型試験体を用い, 窯業製品の熱伝導率を迅速かつ正確に測定するために前報の装置を一部改良し, 各種の試験を行って信頼性を確かめ, かつ測定に要する時間, 測定方法に関する裏付となるデーターを得た. すなわち
(1) サーモペイントを含む微粉アルミナから作った試料を用い, 測定時試験体中の温度分布を調べ, 本装置による測定では試験体中を熱が上面から下面に向って充分一様に, 垂直に流れることを確認し得た. これから熱伝導率の小さい試料でも, 水熱量計を用いる絶対法で, 正確な測定が可能であることを示した. そして温度測定位置の問題についても明確な解答が与えられた.
(2) 本装置は熱流が定常状態に達してから測定を行わねばならないが, 例としてカーボランダム煉瓦のように高い熱伝導率のものでは3時間, 耐火断熱煉瓦 (HW-28級) でも6時間以内で1回の測定が出来ることを示した. そして測定時間が早すぎると熱伝導率およびその温度係数が小さくなることを実際に示した.
(3) 断熱煉瓦の測定でも, 装置と試験体面との接触抵抗は無視出来ないことを示した.
次に本装置, 試験法によってシャモット煉瓦, シャモット質耐火断熱煉瓦, 珪石煉瓦, 安定化ジルコニア煉瓦, 安定化ジルコニア耐火断熱煉瓦, マグネシア煉瓦およびカーボランダム煉瓦に対する測定を行った結果を報告し
(4) 安定化ジルコニア質耐火物について信頼性のある先行研究者の測定結果をも引用して, その熱伝導率と気孔率との関係を示した.
(5) カーボランダム煉瓦については製造方法の差によって極めて大きな熱伝導率の差が現われることを例示した.

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セメントの偽凝結は含有する半水石膏, またはアルミネート類がペースト練りまぜ後早期に水和が進み, ある程度迄硬ばる現象を云う. その現われ方は非常に複雑であり, 例えば粉砕温度が高く半水石膏を形成してもそのままでは一般に練り殺されるが, 風化に伴い炭酸アルカリを形成すると, その遅延作用によってまず偽凝結性となり次いで解消し, 時には引続きアルミネートを急結させ, 終いには不活性化によってふたたび解消するというように多くの要因の影響を受ける.
偽凝結を来たす半水石膏の量は, 共存するアルカリ塩およびアルミネートの形態と量あるいは2水石膏の量等によっても変化するが大凡SO₃1%附近にある. したがって石膏添加量はそれが脱水する可能性を考慮しSO₃1%程度に止め, さらに最適SO₃値に達するまで不溶性無水石膏を併用するのを適当と考える.
偽凝結の測定は練りまぜ後時間の経過とともに貫入度を求めていく方法が望ましい. また風化によって偽凝結を来たすかどうか予知する目的で, 少量の炭酸アルカリ (例えばNa₂CO₃0.1%程度) を添加し測定する促進試験法が考慮される.
本研究に当り御指導を賜わった山内俊吉教授に感謝の意を表する.

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