Application of the photoacoustic spectroscopy is considered to be one of the most usefull methods to characterize the chemical structures of slags, since visible spectra due to transition metals and the optical basicity in slags can be easily measured with this technique.The influences of measuring conditions on the photoacoustic spectra have been investigated by using Cr6+ absorption spectrum observed in CaO-Al2O3-SiO2 glasses doped with 0.2 mol%Cr2O3. It was found that the phase difference of lock-in amplifiers (\varphi) was the most important parameter in a double beam photoacoustic spectrometer used in this study. When \varphi was π/2 rad, the photo-acoustic spectra showed good agreement with the spectra obtained by the conventional transmittance method, and its intensities became maximum. The modulation frequency (ω), another parameter, had strong influence on the intensity of spectrum, which was propotional to ω−3⁄2 in transition spectra of glasses. On the other hand, the intensity of spectrum increased with increasing sample mass and with decreasing powder size of the sample. Especially when the mean diameter of sample was less than 2.0×10−3 m, the intensity of spectrum became steeply large.The optical basicities of alkaline silicate glasses were measured by using Pb2+ as the indicator ion. These results qualitatively agreed with the theoretical optical basicities proposed by Duffy and Ingram. Na2CO3 melted at 1473 K in Al2O3 or MgO crucible showed two optical basicities, 0.68 and 1.11. It suggests that Na2CO3 partly decomposes to Na2O and CO2 at 1473 K, thus 0.68 being the optical basicity of Na2CO3 and 1.11 being that of Na2O.
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