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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The apparatus previously reported in this journal (64, [7] 161-66 1956) was improved and applied for measuring thermal conductivity of various ceramics in temperatures range up to about 1000°C.
(1) By using a special specimen, in which about 15% of thermo-paint is mixed, it was confirmed that the path of heat flow can be successfully controlled to maintain the isothermals parallel within the specimen and thus the heat flow from outside can be eliminated. (Fig. 2)
(2) Tests have shown that steady state is attained in about three hours in the case of high-conductivity specimen (such as SiC brick), while in about six hours in the case of low-conductivity specimen (such as insulating fire brick). (Fig. 3)
(3) In measuring the low-conductivity specimens, the interfacial resistance was found to be not so large, but, nevertheless when we determine the conductivities in neglecting that resistances, we may have data 5-10% smaller than the true value.
(4) Measurement of thermal conductivity for fire bricks, insulating fire bricks, silica bricks, stabirized zirconia bricks, zirconia insulating bricks, magnesite bricks and silicon carbide bricks were carried out. Relation between porosity and conductivity of zirconia refractories is plotted graphically. (Fig. 4)
(5) It is confirmed that silicon carbide bricks made by various manufacturing processes show large variations in the thermal conductivity. (Fig. 6)

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A complicated phenomenon of false setting by aeration of cement will be explained as the results of various factors and interactions between those in the early stage of stiffening due to hydration of plaster of Paris or aluminate.
With increasing of alkali carbonates, for instance, which can be formed by the aeration of cement, and act as a retarder of plaster but simultaniously as an accererater of aluminate, the false setting arises at first, because the plaster setting comes at few minutes after mixing. Later it disappears owing to a severe retardation, and finally actual rapid setting takes place by an accererated hydration of aluminates.
The critical amount of SO₃ in the form of plaster of Paris to give false setting is in the range of ca. 0.8-1.5%, varing not only with the amount and form of alkali salts but with several factors such as the amount of co-existing dihydrate or aluminate. Then it is desirable that the amount of gypsum having a tendency to change to plaster of Paris is limited to about SO₃ 1%, and insoluble anhydrite is added at the same time up to the optimum SO₃ content.
An accerelating test is considered to be available by means of the penetration of paste with addition of small amount of alkali carbonate (for example, nearly 0.1% of Na₂CO₃) in order to detect if a cement will show false setting after aeration.

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