The relationships between the saturation coefficient and frost-resisting properties of Japanese roofing tiles were studied with 95 samples picked from about 1, 000 kinds of tiles produced at several parts in Japan. X-ray diffraction analyses with the twenty representative samples of them and microscopic observations with ten of them were carried out, and the following results were obtained.
a) The highest frost-resisting properties were shown at 0.45 to 0.5 of the saturation coefficient where 96.5% of samples remain safe in 30 times of repeated freezing and thawing tests. The results for samples of the saturation coefficient 0.5 to 0.6 and 0.6 to 0.7 were 21.4% and 0% respectively.
b) The “Kusube” tile in which much glassy volcanic ashes and flustuls were detected microscopically, showed low resisting properties.
c) The samples in which mullite or cristoballite were detected by X-ray diffraction after burnt above 1, 000°C, showed high resisting properties.

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Self-diffusion coefficients of Na⁺ ion in NaPO₃-Al(PO₃)₃ glasses at temperatures about transition points were measured by means of tracer technique using radio-isotope ²²Na.
The counting of radio-activity at successively ground surfaces gave better results than that of powders removed by grinding because of less experimental errors.
The activation energies for the diffusion of Na⁺ ion above and below transition points were 30kcal/mole and 20kcal/mole respectively, which were in accord with the values in silicate glasses and were also agreed with the activation energies for the electrical conductivity of these glasses.
According to a corrected Nernst-Einstein equation, the relation between diffusion coefficient, D_i, and the electrical conductivity, σ, of solid is given by
D_i=σt_ikT/n_iZ_i²e²⋅f
where t_i is the transfer number, k is Boltzmann constant, T is the absolute temperature, n_i is the number of ions per cubic centimeter, Z_i is the valence, e is the electronic charge, f is the correlation factor named by Bardeen and Herring.
The f-value obtained from the author's experiment was about 0.15-0.25, and this value was maintained at temperatures above and below the transition point. It was interpreted, therefore, that the transport mechanism of Na⁺ ion in these glasses about transition temperatures is one of the indirect interstitial (interstitialcy) transport rather than the simple vacancy transport.

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