In order to study the process of devitrification of Al₂O₃-P₂O₅ glasses, three glasses of different compositions ranging between the two extremes, Al₂O₃⋅3P₂O₅; and Al₂O₃⋅P₂O₅, were melted (see Table 1) and after being subjected to the heat treatments of various conditions, were examined by microscopic and X-ray analyses.
The results obtained may be summarized as follows:
1. The crystals produced from the glasses of this system were identified as Al₂O₃⋅3P₂O₅ and Al₂O₃⋅P₂O₅ of high-temperature eristobalite form.
2. Nuclei of the crystalline phases formed only on surfaces of the glass specimens. Their number depended on the composition of glass and the heating temperature (see Fig. 8, 9, and 10). The curve representing the relation between the nucleation-rate and temperature was one to be expected from Tammann's theory concerning the devitrificatin of glass.
3. After the formation of nuclei, crystallites of Al₂O₃⋅3P₂O₅ first appeared and then of Al₂O₃⋅P₂O₅, both of which existed together, mingled with each other, and grew into the radial form (see Photo. 5, 12 and 14; Fig. 4-6). The subsequent crystal growth depended on the composition of glass and the heating temperature, consequently, on the viscosity of glass (see Fig. 4-6).
4. The nearest distance between the neighbouring nuclei and the total amount of crystals in the glass phase were measured and their relations with the composition of glass and the time of heating were given (see Fig. 3-7, Photo. 1-14).

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The effect of firing temperature of Mg(OH)₂ ranging 600°-1500°C on the solubility of MgO in acid solutions and the solubility of synthetic MgO⋅Fe₂O₃ in several solutions at 50°±0.5°C were studied. Mg⁺² and Fe⁺³ ions in the solutions were determined by EDTA method. The results obtained are summarized as follows: the solubility of MgO depends on the firing temperature of Mg (OH)₂, being a maximum at 800° and then decreasing with increasing the temperature up to 1500°C. In the system of synthetic MgO⋅Fe₂O₃ large amount of MgO is dissolved at the initial stage. It is seen that the iron radius, polarizing power of Mg⁺², Fe⁺³ and bond strength between Mg⁺², Fe⁺³ and O^-2 affect the solubility of MgO⋅Fe₂O₃.

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When a lithium containing photosensitive glass is exposed to ultraviolet light and then subjected to the heat treatment, it changes into a polycrystalline material characterized by its good mechanical properties (S. D. Stookey. Ind. Eng. Chem., 45, 115 (1953)).
The purpose of this paper is to present the relation between the mechanical strength and the grain size of the constituent crystallites of the resultant material.
Glass specimens (2.5×5×50mm) of the oxide composition SiO₂ 81, Li₂O 12.5, K₂O 2.5, Al₂O₃ 4, CeO₂ 0.03, Au 0.027% (wt.) were exposed to ultraviolet light by placing them at a distance of 10cm from a 500 watt high pressure mercury lamp for 2 to 1000 min. After the exposure they were heated at three steps; first at 510°C for 30 min. to cause formation of gold nuclei, then at 620°C for 60 min. to cause crystallization of lithium metasilicate partially (40%) from the base glass, and finally at 900°C for 60 min. to convert almost the whole of the base glass to polycrystalline materials consisted of lithium disilicate and β-quartz. The grain size of the constituent crystallites of the resultant material was able to be varied from 0.85 to 2.3μ by changing the U. V. exposure time (Ref. M. Tashiro and S. Sakka. J. Ceram. Assoc. Japan, 67, 263 (1959)).
Tests for bending strength and Vickers hardness were made with two classes of specimens, one which completed a whole course of the above heat treatments and the other which completed only the first half of the heat treatments, i.e., heated only up to 620°C.
The tests have shown that, for the specimens which completed the whole course of the heat treatments, crystallization increases mechanical strength of the specimens, and the relation between the average grain size of the constituent crystallites (d) and the mechanical properties (M) (both of the bending strength and Vickers hardness) is given by the equation,
M=const⋅d^1/2.
For the specimens heated up to 620°C, partial crystallization of the glass phase was found to increase the mechanical strength of the specimens but in somewhat more complex way. This was attributed to the effects of glass phase still remaining in considerable amounts (60%) in the specimens.

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In the previous papers (J. Ceram. Assoc. Japan, 67 [1] 16-20 (1959); J. Ceram. Assoc. Japan, 67 [12] 399-403 (1959)) it was shown that the pretreatment of the aluminium surface by the anodic oxidation improved the adherence of vitreous enamel to the metal surface.
This report contains the results of investigations of the effects of this pretreatment on the physical properties of the finished products. The surface configuration of the aluminium plate subjected to this pretreatment was examined with the electron microscope in order to throw light on the cause of the strong adherence of enamel to the metal surface.
The results obtained may be summarized as follows:
1. The anodic oxidation produced the rough metal surface having reticular micro-ditches (see Photo. 2 and 3) which would improve the adherence between enamel and the metal.
2. The pretreatment of aluminium plate gave good results with respect to the adhesive properties, the color, and the luster of the finished products. Optimum firing time for borosilicate and lead enamels (see Table 3) were both about 30 sec. at 500±10°C (see Fig. 2).
3. The pretreatment of aluminium plate was found to be effective in suppressing blistering produced at the enamel-interface during firing.

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