In order to observe the deformation behaviour and further to follow qualitatively the change of viscosity and the surface tension of high feldspathic bodies in the feldspar-quartz system, small tablets, 20mm in diameter, consisting of 100-75% potash or soda feldspar and 0-25% quartz were fired in an electric furnace, and then abruptly cooled in air. Degrees of deformation of the fired specimences were measured on their vertical section, as shown in Fig. 1, microscopically and then the course of their deformation was plotted on a diagram.
From the diagrams obtained, following results were concluded.:
(1) Viscosity and surface tension of the bodies of feldspar-quartz system are decreasing with increase of firing temperature and soaking time.
(2) Bodies of soda feldspar-quartz system have markedly lower viscosity than those of potash feldspar-quartz system and with rising temperature, the formers also show more remarkable decrease of their viscosity than the lotters do. While in the bodies containing more quartz than 20-25%, soda feldsparthic bodies rarely show a little higher viscosity than the potash feldspathic ones.
(3) The surface tension of the bodies of soda feldspar-quartz system is higher than that of the bodies of potash feldspar-quartz system, but lowering of the former's surface tension with rising temperature is more striking than the latter's.
(4) Flow point of soda feldspar specimen, fired with the rate of 60°C/hr, is 1270°-1280°C, and this is markedly lower than that of potash feldspar, which is 1350°-1360°C.
(5) Viscosity of the bodies of feldspar-quartz system is increased with the increase of their quartz content. The increase is more remarkable and regular in soda feldspathic bodies. Tendency of this viscosity increase is reduced with rising temperature, or with prolonged soaking.
(6) Bodies consisting of 90-95% potash feldspar and 10-5% quartz show a distinguishedly large deformation than anyother's, therefore “deformation eutectic”, while no such phenomena in the bodies of soda feldspar-quartz system.

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As a continuation of the author's previous papers on “The Effect of Grain Size Distribution” and “The Effect of Chamotte Content” on the Physical Properties of Pot Materials used for Optical Glass Melting, the effect of eight kinds of clay raw material covering kibushi-clay, gairome-clay, koalin and roseki-clay as well as the effect of their mixing ratio on the physical properties were studied for seventy-one different pot materials in which the grain size distribution and the content of the chamotte were kept constant.
After measuring the chemical composition, the distribution of grain size, and the buffering action of clays used, the content of water glass, used as the dispersing agent, was determined so as to make the slip to have constant fluidity while keeping the water content of the slip as small as posible. In the measurement both the method of determining the limiting water content for flow, and that of measuring the time of flow of the slip by funnel were employed, and by these determinations following facts were clasified: (1) Kaolin and roseki-clay can be dispersed in the water glass of the quantity 1/2 to 1/10 of kibushi-or gairome-clay. (2) The fluidity becomes low, for any kind of the clay used, when a part of the water-glass is replaced by soda containing the same quantity of Na₂O. (3) In mixed clay materials the highest fluidity is obtained when the water-glass content is equal to that culculated additively from the content of water-glass to give the highest fluidity for each component clay. (4) For dried or burned clay samples cast from clay slips having equal water content and different water glass content, those cast from slips containing water-glasses of highest fluidity are not densest. It was formd that the drying properties of pot materials, cast in the way mentioned above, did not change remarkably by the replacement of kibushi by gairome-clays and vice versa. They showed, however, remarkable change by the substitution by kaolins. Hence, the use of kaolin is limited and it must be used with care, while roseki-clay may be used much more easily in the range of the content below 20 per cent.
For pot materials burned for 2 hours at 1500°C, although the burning shrinkage and the apparent density changed additively with the addition of clay, the denseness, represented by apparent density and porosity, showed the tendency to become dense by the addition of clay raw materials, except for two kinds of gairome-clay used. Althou gh kaolin increased the burning shrinkage and the apparent density of pot materials, the degree of increase is less compared with the effect on their drying properties, and roseki-clay made pot materials to have low firing shrinkage and to be dense.
The strength of burned pot materials are generally increased by the addition of clay, especially when Korean-Koalin was mixed with respective kibushi-or gairome-clay, pot materials became extremely strong at about 30 per cent of Korean-Kaolin content, and roseki-clay also made then strong in the range up to 20 per cent, of its content. Although the strength of pot materials quenched at temperatures when the pot is pulled out of the furnace after the glass is melted or when the glass batch is thrown into the pot was not so much changed as the case when they are showly cooled. They were stronger when they had larger content of kibushi-or gairome-clay and they were weak when they had large content of koalin. The spalling resistance expressed by the ratio of the strength of quenched to that of slowly cooled materials, showed the general tendency that the larger the strength of slowly cooled materials, the smaller the spalling resistance, although dense materials were not always weak in spalling and materials having 12-16 percent porosity were relatively strong.

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