In the present paper studies were carried out on fluxing materials for the graphite crucible. At first, by the practical service test for the foundry, it was observed that the quality of graphite crucibles was greatly affected by fluxing materials, and borosilicate glass with a little amount of cryolite had excellent effects as a fluxing material.
In order to confirm these results, a lot of test rods of various compositions were prepared, and their physical properties, i.e. bulk density, water absorption, hardness, electrical resistivity, bending and compressive strength were measured.
The properties of test pieces were affected by fluxing materials and firing temperature. The piece with borosilicate glass and a little amount of cryolite showed very satisfactory characteristics, especially for water absorption, bending and compressive strength, and these physical properties improved with the rise of firing temperature. The tendency was most remarkable between 1100°C-1200°C.
As for the oxidation test, the quality was also affected by fluxing materials. The weight change was the smallest for the piece with borosilicate glass and a little amount of cryolite, and this was made remarkable with the rise of temperature and also with the time of oxidation.
These experimental results based on the test pieces showed coincidence with those of the practical service test for the foundry.

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Effective retarding agents for cement mortar have been recently required to transport the ready mixed concrete, because only the addition of gypsum is not sufficient for prolonged time owing to the traffic confusion in large cities. It was previously confirmed by the authors that the addition of 0.5 to 2.5 percent of sodium sulfite retards the setting of the cement mortar twice as long. The addition of sodium sulfite was found moreover to have a favorable effect on the strength at the early stage.
As a basic study of the retardation of the setting by sodium sulfite, the hydration process of tricalcium aluminate and tricalcium silicate in sodium sulfite aqueous solution has been investigated by heat measurement, electron microscopic observation and X-ray diffraction analysis. The measurement of heat liberation was made by a calorimeter devised by us on pastes of the following composition at 35°C±0.01°C for 5 hours;
(1) C₃A+Na₂SO₃aq.
(2) C₃A+CaSO₄2H₂O+Ca(OH)₂+Na₂SO₃aq.
(3) C₃S+Na₂SO₃aq.
(4) C₃S+CaSO₄2H₂O+Na₂SO₃aq.
Na₂SO₃aq.:0, 0.5, 1.0, 5.0, 10.0%
Sodium sulfite in a dilute solution depressed effectively the hydration of tricalcium aluminate, whether in the presence or in the absence of gypsum and calcium hydroxide On the other hand, in a concentrated solution tricalcium aluminate reacted directly with sodium sulfite and formed aluminum hydroside gel in the paste. This precipitated aluminum hydroxide gel, coagulating and enclosing the tricalcium aluminate grain, caused “gel set” (flash set).
Likewise, in the hydration of tricalcium silicate in 5.0 and 10.0% sodium sulfite aqueous solution, “gel setting” is caused by the direct reaction between calcium silicate and sodium sulfite. Sodium sulfite in a dilute solution accelerated the hydration of tricalcium silicate, which are similar to the action of gypsum on tricalcium silicate in pure water. In the presence of gypsum, the addition of a dilute solution of sodium sulfite depressed greatly the hydration of tricalcium silicate.
The reason why the hydration of tricalcium silicate is retarded by the dilute solution of sodium sulfite in spite of the presence of gypsum, is seemed to be understood by the following explanation. The direct reaction between tricalcium silicate and sodium sulfite will proceed with the formation of calcium sulfite and soluble sodium silicate. A subsequent reaction between tricalcium silicate and gypsum dissolved in liquid will take place precipitating silica gel or gel-like calcium silicate hydrates. These gel-like substances will temporarily enclose tricalcium silicate grains, thus the hydration is retarded. It seems that the action of dilute solution of sodium sulfite on the hydration of tricalcium silicate in the presence of gypsum is interesting in respect to as an additional retardation for the cement hydration.
Mortar and concrete tests which were carried out concurrently, gave results which agreed with the above-mentioned experiment.

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H. M. Cohen and Rustum Roy reported that silica glass densified under ultrahigh pressures with the opposed anvil apparatus shows no relaxation effects even when heated at 600°C (J. Am. Ceram. Soc., 44 [10] 523 (1961)). J. D. Mackenzie, however, has found recently that marked relaxation occurs at the beginning of reheating at above 300°C for silica glass densified with the high-pressure “Belt” apparatus (J. Am. Ceram. Soc., 46 [10] 461, 470 (1963)). In the present work Mackenzie's result has been confirmed for silica glass and a borosilicate glass both densified with the same opposed anvil type pressure apparatus as used by Cohen et al.
Samples of the silica glass were taken from a commercial clear grade silica glass rod. The borosilicate glass with the composition of Na₂O 7.5, B₂O₃ 22.5, and SiO₂ 70% in weight, was melted in a platinum crucible. The glasses were pulverized to 40-50μ, pelleted into a disc of approximately 6-mm diameter and 0.2-mm thickness, wrapped in a platinum foil, and pressed between two opposed anvils of the high-pressure apparatus at temperatures ranging from 25°C to 300°C for various periods. The pressure was released after the temperature of the sample was lowered to room temperature. The annealing of the densified glasses was made by reheating under atmospheric pressure at temperatures ranging from about 130°C to 900°C for various periods. Refractive indices of the reheated glasses were measured as the indication of relaxation.
The results showed that the relaxation becomes noticeable by reheating above approximately 300°C for the silica glass and at much lower temperatures than 300°C for the borosilicate glass. In both cases the relaxation completes almost in a few minutes at the beginning of reheating.
The activation energies of the relaxation process calculated from the initial changes in refractive indices were approximately 10 and 3kcal/mol for the silica- and borosilicateglasses respectively, which were both much lower than the activation energy of viscous flow in these glasses.

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