Two important characteristics for pots used in melting optical glasses are those of durability against molten glass and of spalling. Present paper deals with the latter property and its bearing on the composition, especially the influence of the grain size distribution of chamotte. Grains of chamotte studied may be classfied as to their sizes as coarse, medium, fine, and very fine. (ratio of their diameters is roughly 14:5:2.5:1). State of dense packing can be obtained for mixtures plenty of grobe and very fine grains and meagre of medium or fine grains in mixtures of three kinds of grains, coarse-medium-very fine and coarse-fine-very fine. Casting slip made of these mixtures with clay have features as follows:
i. The fluidity of casting slip is best when the grain size distribution of the slips do not incline toward coarse or very fine.
ii. Drying characteristics of bodies run parallel with surface factor calculated after Jackson and Purdy, and are influenced by the state of chamotte packing.
iii. Spalling characteristics at temperatures of 850°C (at this temperature, pot is sprayed with water after melting) and 1350°C (at this temperatures batch is poured in) are good by bodies not inclined toward coarse or very fine.
iv. Firing characteristics of bodies run parallel with surface factor but are not affected from the state of chamotte packing.

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On continuing the previous studies (This Journal, 62 [696] 403-406 (1954); 63 [714] 523-527 (1955)), the authors report in the present paper the results of further studies on various properties of fly ash by comparing with other siliceous pozzolanic admixtures used in the previous reports (loc. cit.). The collected samples were three kinds of fly ash from electric power plants (Chicago fly ash from America, Ube fly ash from the Ube Kosan Co., and KFA fly ash from the Kansai Denryoku Co.), one coal ash KPA quenched in water pond from the Kansai Denryoku Co., and two kinds of natural siliceous pozzolanic materials (Beppu-hakudo and Oya-ishi used in the previous reports (I) and (II)). These samples were analysed and compared by the common total and special soluble analysis. The testing of lime-adsorption and the electron microscopic photographs gave clear difference between fly ash and natural siliceous pozzolanic materials. The test of swelling in distilled water or in lime water, the alkalinity test, the bending and compressive strength tests by the standard 1:2-cement sand mortar, and the bleeding test (ASTM Proc., 49, 891 (1949)), etc., gave clear aids for the discrimination between true fly ash, pond ash and other siliceous admixtures.

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Thermal expansion of synthetic cordierite was determined along a and c axes respectively, with the aid of Geiger Counter X-ray Diffractometer in which a small electro-furnace was settled. From room temperature to 140°C, a₀ was fair enlarged but c₀ was remarkably diminished. This fact seems to be responsible for the negative expansion at the lower temperature in cordierite porcelain. From 140°C to 303°C, a₀ and c₀ were simultaneously enlarged. From 303°C to 555°C, c₀ was enlarged as before, while a₀ ceased the further enlargement at least within this temperature scope. This may suggest the presence of a prompt type inversion of this crystal during the heating.

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It was found that the transformation of siliceous stone, from quartz to cristobalite, was the primary reaction. The rate constants of the conversion of several siliceous stones (contrasted origin) were calculated. Influence of grain sizes on the velocity of the conversion was investigated. The effect of irreversible thermal expansion of the unisotropic polycrystal aggregate to its apparent density is calculated theoretically, and experimentally measured. Accurate determination of the transformation verocity, and experimentally measured. Accurate determination of siliceous stone has became possible by taking the effect into consideration.

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