Heating gypsum below 100°c gives rise to limiting values of weight loss around that of the hemihydrate formation whatever is the time of heating. Calcination at 100°c and above, on the other hand, causes a continuous loss in weight as the time is prolonged, leading to γ‐anhydrite when adequate time is given. In most of the examined samples a resistant state, with trace amounts of residual water, is reached towards the end of the dehydration process. Such residual water is driven off completely below the transformation temperature of γ‐ to β‐CaSO4.

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A comparatively high steam pressure should be used to give complete sodium silicate formation from the starting materials. Moreover, a higher steam pressure is required in the case of using sodium carbonate than on using sodium hydroxide. Sodium metasilicate hydrate prepared under a low steam pressure (2.5 atmy appears to be amorphous in nature while that prepared from sodium hydroxide or sodium carbonate at a higher steam pressure is crystalline and very similar to the metasilicate hydrate with the formula Na2Si03. 9H20. However, the metasilicate prepared from sodium carbonate appears to be poorly crystalline due to the presence, in the prepared material, of an appreciable amount of sodium carbonate.

A comparatively high steam pressure should be used to give complete sodium silicate formation from the starting materials. Moreover, a higher steam pressure is required in the case of using sodium carbonate than on using sodium hydroxide. Sodium metasilicate hydrate prepared under a low steam pressure (2.5 atmy appears to be amorphous in nature while that prepared from sodium hydroxide or sodium carbonate at a higher steam pressure is crystalline and very similar to the metasilicate hydrate with the formula Na2Si03. 9H20. However, the metasilicate prepared from sodium carbonate appears to be poorly crystalline due to the presence, in the prepared material, of an appreciable amount of sodium carbonate."Throughout this paper 1 atm E 101 kN/m2. 659