Reactions of sodium sulphate, calcium sulphate and sodium sulphite in glass batch were examined by means of DTA, TGA, and the crucible melting test. Batches for sheet glass to which a small amount of sulphate or sulphide was added were melted and the amount of residual silica and distribution of silica grains were observed. The crucible melting tests indicated that sodium sulphite did not show much effect in helping homogeneous distribution of silica grains within the glass melt, which was seen in the case of sodium sulphate, while calcium sulphate exhibited the effect similar to that of sodium sulphate. The DTA and TGA showed that sodium sulphite was easily decomposed or oxidised at temperatures around 700 deg C or lower. Moreover, the decomposition and oxidation depended considerably upon the atmospheric conditions.
