The effect of long grinding on quartz (silver sand)

Abstract

It has been shown from determinations of the heats of solution that when silver sand is subjected to grinding for a long time in a mechanically operated agate mortar, it partially loses its crystalline structure and is converted into the vitreous state. The value of the molecular heat of solution of quartz (silver sand), after grinding for 15 hours, was found to be 2.17 kgrm.-calories higher than that obtained for material which had not been subject to grinding. The difference between the molecular heats of solution of quartz and vitreous silica is 6.95 kgrm.-calories, so that 31.2 per cent, of the material is converted into the vitreous state by 15 hours’ grinding. In the course of the discussion on the paper, it was suggested that, as there was considerable difference between the densities of quartz and silica glass, the measurement of the densities of the ground and unground materials ought to show a difference, if any considerable change from the crystalline to the vitreous state really took place. The following experiments were undertaken in order to settle this point. In the preliminary experiments, it was found that consistent results could not be obtained in the case of the ground silver sand, when water was used as the liquid for determining the volume of the material. Considerable difficulty was also experienced in removing the adhering air when attempt was made to determine the density in the usual way with a specific gravity bottle. The following method, which was finally adopted for determination of the densities, gave fairly good results: A small bulb of about 10 c.c. capacity was blown at the end of a short capillary tube, the internal diameter of which was about 0 5 mm. The bulb was steamed out for nearly 20 minutes, and then heated at 300° for 24 hours so as to eliminate contraction of the glass. The capacity of the bulb was determined by filling it up with water. The liquid used for determining the volume of the materials was carbon tetrachloride, which had been re-distilled after digesting with calcium chloride for a long time. All the densities were determined at the air temperature 16°-17'6° C. The following values were obtained for the density of carbon tetrachloride: (1) . . . . . . . . . . . . . . . . . 1.597 (2) . . . . . . . . . . . . . . . . . 1.601 } Mean, 1.599 (3) . . . . . . . . . . . . . . . . . 1.599