It was pointed out in previous papers (J. Ceram. Ass., Japan, 68 [10] 237; [12] 294 (1960)) that the mol ratio, MgO/SiO₂, of the substance scattered from the furnace during the operation changes with the composition of molten dunite, and for which have given some considerations on the process of scattering.
This paper contains the results of the studies of scattered substance, i.e. mineral composition, change by heating, form of particles, by means of X-ray and differential thermal analysis, thereto-gravimetric, and the observations under electron microscope.
The results are as follows:
(1) The scattered substance was composed mainly of forsterite and periclase accompanying Si or SiC especially when the material was rich in SiO₂. At the early stage of electro-melting the substance contained a large amount of amorphous and nearly amorphous substances. By heating at 700°-800°C the formation of forsterite, and at 1000°-1100°C the increase of the rate of conversion to α-cristobalite were confirmed.
(2) The scattered substances contained more or less the lower oxides of Si, especially in larger amount in the early stage of electromelting.
(3) The scattered substance was composed of the fine spherical and cubic particles of the size 0.05-1.5μ, although the external form changed with the composition and also with the time and the method of sampling.
(4) As far as the present experiment is concerned it was observed that the scattered substance became more and more rich in MgO with the time of melting, i.e. with the elevation of furnace temperature. At the same time the powders showed the trend of becomming larger in size.
(5) The unstable lower oxides contained in scattered substance was able to be converted to stable higher oxides by allowing sufficient time to contact with air or oxygen during the sampling.

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As a part of the study of binary system, CaO-Cr₂O₃ the reactions which occur when mixtures of CaCO₃, Ca(OH)₂ and Cr₂O₃, CaO⋅Cr₂O₃ and CaCO₃ fired in air were investigated using differential thermal analysis, thermal balance, and X-ray diffraction analysis at room and high temperatures.
The results obtained are summarized as follows:
(1) When the mixtures of Ca(OH)₂ and Cr₂O₃ were heated in air an oxidation reaction has occured at about 720° with the formation of CaCrO₄ showing an exothermic peak in the thermal curve. In the case of mixtures CaCO₃-Cr₂O₃ decomposition and oxidation occured simultaneously at the temperatures between 700° and 900°C giving the thermal curves with two or three peaks.
(2) From the relations of weight loss against the ratio CaCO₃/Cr₂O₃ and from X-ray data the compounds formed during the heating may be estimated.
By heating in air up to 1000°C CaCrO₄ was formed from the mixtures of CaCO₃/Cr₂O₃=0.33-2, and a new compound “X” from those of 2-4, and only “X” when the ratio was larger than 4.
“X” was not the same as 9 CaO⋅4CrO₃⋅Cr₂O₃, a compound given by Ford and Ree (Trans. Brit. Ceram. Soc. 41, 207, 1948), but a higher oxidized compound. From the weight loss curves of mixtures CaCO₃/Cr₂O₃=4-6 the composition of “X” was calculated to 18CaO⋅10CrO₃⋅Cr₂O₃.
The mixtures of CaCO₃/Cr₂O₃=2-4 showed a secondary loss in weight at a temperature between 920° and 1000°C corresponding to an endothermic peak at 950°C in the diffrential thermal curve. Also high temperature X-ray analysis has revealed that the change was a reversible phase transformation. This may be regarded as a decomposition of 18CaO⋅10CrO₃⋅Cr₂O₃ with O₂-loss at the presence of CaCrO₄. The stable form at high temperatures should have the lattice belonging to simple crystal system, since the number of lines in the diffraction pattern were few.
(3) CaO⋅Cr₂O₃, which appeared as green needle, anisotropic crystals showing straight extinction could be obtained easily by acid treatment of the mass produced by keeping molten for 3 hours the mixture 2CaCO₃+Cr₂O₃ at 1300°C. At 1000°C CaO⋅Cr₂O₃ was oxidized partially giving CaCrO₄, and the mixture, CaCO₃+CaO⋅Cr₂O₃ showed a phase transformation at 960°C.

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A proposed method of determininig free Na₂O in the hardened bodies made from sodium silicate solution and Na₂SiF₆ is described, in which samples containing not more than 2mg of Na₂O are ground in an agate mortar with 5ml isopropyl alcohol, poured into 100ml beaker using 50ml of said alcohol, therein mixed with 20ml of 0.25N HCl solution saturated with BaCl₂ for 3 minutes, then the whole mixtures are titrated with 0.3N NaOH solution until the colour of mixed indicator of dimethyl yellow and methylen blue changes from blue-violet to clear green.
Using this method, the reaction processes occuring in the mixtures of Na₂SiF₆ and the sodium silicate solutions having molar ratio of SiO₂/Na₂O ranging 2.8 to 3.5 and the solid content ranging 14% to 38% were studied with the following results:
The reaction proceeds with the rate of first order, whose constant, k, varying with the solid content of sodium silicate solutions employed, may expressed as k=k′e ^-βC₀t and leads to an equation
-ln(1-x)=k′e^-βC₀t
where x is the fraction converted, c₀ is the solid content of sodium silicate solution, t is the time in hour after mixing, and k′, β are constants.
The reaction obeys the Arrhenius equation in which the mean activations energy was caluculated to be 7.87 kcal/mol in the range of 10°C to 40°C.
The reaction stops eventually at about 80% conversion, irrespective of the measure of rates, which may be attributed to the thorough coagulation of sodium silicate in the hardened bodies by the salt effect of NaF produced.

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In previous report the author has derived an equation for calculating the principal stresses in a glass seal between two metal tubes, which is avairable for the design of glass-to-metal seals.
In this paper the theory is extended to the case of the glass sealing between three concentric metal tubes, which covers the wide range of the expansion coefficient of glass and metal.
The experimental background of the theory has been furnished by photoelastic study.
The results have proved that it is desirable to use an external metal cylinder of large thermal expansion in order to give a large compression in glass, although a large difference in the expansion of glass and internal metal cylinder should be avoided because of the shearing stress.
The stress calculated from the thermal expansion of sealing members are large compmared with the observed values measured by photoelasticity. This difference may be attributed to the “end dffect” of short cylinders, although the theory is practically useful for the design of the seals of this type.

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Kaolin minerals were mixed with 0.1, 0.2 and 0.4mol of minerallizers. The crystal phase of the heated samples was examined by X-ray and differential thermal analysis.
It was found that the temperature of the endothermic reaction of kaolin minerals containing fluoride was higher and the temperature of the exothermic reaction was extremely lower than that of the thermal reaction of original kaolin minerals. The variation of the endothermic reaction was found to be related to the crystallinity of kaolin minerals, and was large in well-crystallized kaolinite in contrast with the variation in poorly crystallized kaolinite or halloysite. These thermal reactions may be due to the effect of fluorine ion in the minerallizers. Furthermore, the kaolin minerals containing fluoride was found to form a mullite type phase at much lower temperatures, so that a small amount of mullite type phase was recognized even at 550°C, when 0.4mol of LiF was added to kaolin minerals.
The samples heated at 600°-900°C were then treated by 5-10% of hydrofluoric acid to separate mullite type phase. The cell dimension of these samples was measured and some indications of the composition of the mullite type phase were obtained from the relation between unit-cell volume and cell edge c. The results indicated that the mullite type phase formed at lower temperatures in the kaolin minerals containing LiF is composed of the crystals of normal mullite (3Al₂O₃⋅2SiO₂).

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