Circular plates measuring 10cm in diameter and 0.5 to 0.8cm in thickness were formed under a total pressure of 15tons from wet powder composed of each 0 to 100% of Korean kaolin, Kawamata feldspar, and Shijonawate quartz. After firing to cones 02a, 8, 10, 12, and 14, they were tested for thermal conductivity at mean temperatures ranging between 60 and 70°C by the method of Prof. Shiro Nukiyama in which the thermal conductivity of test piece is compared with that of a standard glass plate. Then the conductivity of the test pieces was calculated for zero porosity to find the relation between their chemical composition and the mean conductivity of the test pieces fired to cone 8 to 14.
The results seem to justify the following conclusions:
1. The calculated thermal conductivity of the bodies fired to a low temperature as cone 02a is almost same regardless of their composition.
2. In the bodies fired to comparatively high temperatures as cone 8 to 14, the calculated conductivity is only slightly affected by the proportion of kaolin and quartz, whereas it is distinctly reduced by an increase in feldspar.
3. The calculated conductivity of the bodies lies within the range of those of raw materials.

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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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