Heat of crystallisation of quartz

Several attempts have been made to determine the heat of crystallisation of quartz, or the heat of transformation of quartz into vitreous silica, which is of importance in calculating the heat change involved in silicate reactions, and conflicting results have been obtained by different workers. Tschernobaeff determined the heats of formation of certain silicates by Le Chatelier’s method, measuring the heat evolved when a mixture of the dry substances were made to react by combustion of a given weight of carbon in a bomb calorimeter. From the difference of heat of reaction of silica glass and calcium carbonate, and of that of sand and calcium carbonate, Tschernobaeff found that the heat of transformation of quartz into vitreous silica was very small, and equal to only 0.9 Kgrm.-cals. per grm.-molecule. But from the results published later by Tschernobaeff and Wologdine Dr. M. W. Travers has calculated the heat of transformation of silica and found it to be equal to 7.3 Kgrm.-cals. From the measurements of conductivity, Tammann showed that amorphous and crystalline silica dissolved in hydrofluoric acid in one and the same state, so that the difference between the heats of solution of the two substances would represent the heat of transformation from the crystalline to the vitreous state. Cunningham was the first to use the hydrofluoric acid method for this purpose. His experiments, however, were more or less of a qualitative nature, but he stated that he obtained a distinct indication of a large difference between the heats of solution of crystalline and vitreous silica.