Rindone found that a small amount of platinum (0.01%) introduced into a glass of the composition Li₂O⋅4SiO₂ acts as a nucleating agent of repeating, converting the whole mass into an assembly consisting of extremely small crystals (G. E. Rindone, J. Am. Ceram. Soc., 41, 41 (1958)).
This paper presents the results of the investigation of authors which covers the nucleation by platinum for glasses containing Li₂O, MgO, Al₂O₃, and SiO₂. The bending strength was used for the evaluation of the effect of the nucleating agent.
(1) Optimum amount of platinum The glasses of the composition, Li₂O 12.5, K₂O 2.5, Al₂O₃ 4, SiO₂ 81% by weight, added, respectively, with 0, 0.001, 0.01, 0.1% of platinum were formed into the specimens of the size 50×5×2.5mm. Taking the density increase as a reference the effect of the concentration of platinum on the devitrification of the specimens under a stepwise heat treatment was investigated. It was found out that 0.01% was sufficient for the completion of devtirification (Fig. 1).
The bending strength of the devitrified specimen increased with increasing platinum content (Fig. 2). Taking into consideration of the cost of platinum the authors concluded that 0.01% is the optimum amount for nucleation from practical stand point.
(2) The influence of lithium content The glass of the composition, MgO 15, Al₂O₃ 23, SiO₂ 62=100+XLi₂O, whereX=4, 6, 8, 12, by weight, was melted with and without addition of 0.01% platinum. The specimens of the same size as above were heated from room temperature to 1050-1100°C with the rate of 5°C/min., and then kept constant for one hour. The bending strength of platinum containing glasses increased remarkably when their lithium content was high (12%), whereas only a negligibly small increase wasfound in the glasses of low lithium content below 6% (Fig 7). This indicates clearly that the function of platinum was influenced by the amount of lithium in glass.
It was also conformed that the glasses of tow lithium content could be converted into a polycrystalline material of high mechanical strength even when no platinum was added (Fig. 7). The investigation of this interesting phenomenon is now going on.
(3) The optimum composition range in the system Li₂O-MgO-Al₂O₃-SiO₂. Keeping Li₂O at a constant value of 12% other components were changed as; MgO x, Al₂O₃ y, SiO₂ z, where x, y, z are mole ratio by weight and x+y+z=100, the range in which; the two conditions, (a) glass may be obtained at a melting temperature lower than 1400°C, (b) the glass converts into the polycrystalline material without any noticeable deformation during the reheating will be satisfied. The range in which the condition (a) was satisfied was x: 0-30, y: 0-30, z:60-100, (Fig. 8), and that of satisfying (b) was x: 0-20, y: 0-30 and z: 60-100 (Fig. 9 and Table 1).

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The glasses of the system Na₂O-B₂O₃-SiO₂, with or without the addition of Al₂O₃, were melted in a platinum crusible using refined silica and chemical reagents.
The quenched glasses were subjected to the repeated heating at a constant temperature in the range of 350°-633°C, and the densities were measured by sink float method. The change of density was analysed in conformity to the theory advanced by the author (J. Ceram. Assoc. Japan, 66, 117, (1958).
The change of density ΔD may be expressed by an equation
ΔD=Σp_ie^-t/φ_i=pe^-t/φ₄+qe^-t/φ₃+re^-t/φ₂+se^-t/φ₁+……, where t is the time, φ the relaxation time containing a certain activation energy, and increase with decreasing temperature. pe^-t/φ₄, qe^-t/φ₃ represent the decrease of density.
The author assumed that both termes represent the density change due, respectively, to the growth of the phase separated out by heating at an elevated temperature, and to the separation at lower temperatures. re^-t/φ₂ was considered as the density increase due to the compacting of quenched glass brought about by the recombination of atoms in the comparatively open stracture.
The activation energies in φ₄, φ₃, φ₂, are of the order of 80kcal/mol, and se^-t/φ₁ is regarded as the primary cause of the density increase at the temperatures considerably lower than the transformation region. It has low activation energy.
In the same way as given in a previous paper (J. Ceram. Assoc. Japan, 61, 178, (1959)) it was possible to elusidate the above characteristic properties of density change by introducing the reaction model composed of the energy levels, L₁, L₂, L₃, L₄, which is corresponding, respectively, to the quenched state, compacted state, and those of separation at comparatively lower and higher temperatures, and assuming that L_i is composed of two closely adjoined energy levels l_i1 and l_i2.
Furthermore, the opalisation and the surface devitrification of the same glass were studied with some results on the relation between the separation and the characteristic features of phase diagrams.
As far as the composition range of present paper is concerned the borosilicate glasses did not show any trend of progress from separation to crystallization, except on the surface layer.
Moreover, the measurement of thermal expansion and of density change have revealed that the addition of Al₂O₃ checks the excessive development of the size of separated phase.

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The refractories made from dunite shows usually the complicated change of microstructure during the furnace campaign due to the change of temperature and atmosphere. This may lead to the complete collaps of the whole structure, and is the very reason which has checked its practical use.
R. L. Stone and also Ikenoue suggest that the iron, existing in the state of solid solution in the mineral, would be the main source of the occurence of such damage. The author has carried out the investigations for the purpose of improving the instability by taking away the iron through the electric melting under reducing condition.
The present paper concerns the observation of the author on the process of remove of iron and silica by the electromelting of dunite from Fukushima prefecture. Especially on the influence of the reducing agent (carbon powder and the powder of pig iron) on the structure of electro-molten dunite is discussed. It was confirmed that the size of forsterite crystals in the mass obtained by electric melting reduced their size with the increasing amount of the reducing agent.
Above all it would be worthy of noted that the separation of periclase crystals was observed in the mass reduced by iron, and the probable existence of close relation between the compositions of the dust and the ingot obtained by electro-melting was also noticed.

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A rapid Method for the evaluation of the amount of Portland cement in fresh concrete by measuring the specific gravity of mortar suspension is described.
This method is characterized by two features, viz. (1) using three hydrometers according to cement content, and (2) measuring the height of sand sediment in mortar suspension simultaneously with the measurement of density.
A control curve was constructed through follwing procedures: As the first step the amounts of cement in 1:2 mortar were determined by experiment, which satisfy the condition that the hydrometers of different measuring range go to the same depth into the suspension. Then the specific gravities of 1:1 and 1:3 mortar suspensions containing the same amount of cement as before were measured using the three hydrometers. Lastly, the three curves as shown in Fig. 5 were drawn to corelate the 9 values of specific gravity with the cement content. Using the control curve it is thus possible to estimate the amount of Portland cement of any fresh concrete if sand content were known, which the authors estimated from the height of sand sediment.
The estimation of cement content in the fresh concrete, which had been prepared in laboratory by hand mixing (not in a concrete mixer) and with various mixing proportions have been carried out. The error as a mean was found to be 2% (-1.1, +5.3%) or 7kg/m³ concrete (-5, +25kg/m³).

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