In Japan it was a common practice that a small amount of sodium chloride was added during the calcination of limestone in order to obtain quicklime good for the preparation of dry hydrate of lime. It was found that the salt vapour enhanced the crystal growth of calcium oxide and made the quicklime less sintered or more porous aggregate than those calcined without the salt. Alkali and alkaline-earth halides were also found to enhance the crystal growth of the oxide and other refractory oxides such as magnesia, alumina, and spinel. Among the halides alkali fluorides had the largest effects. Fluorides are the well-known fluxes or mineralizers for mineral syntheses. Mica, one of the principal rock-forming minerals, can be synthesized from melts containing fluorides. Fluorine ion substitutes hydroxyl ion in the crystal lattice of mica. For the purpose of the preparation of large single crystals of fluor-mica, temperatures of crystallization and rates of crystal growth of the mica from melts were measured. Large scale melting experiments were carried out using an electric resistance furnace. Successful growth of clear mica booklet was accomplished with a moving crucible technique using seed crystals of fluor-phlogopite. Experiments to prepare single crystals of graphite were carried out by a) the solidification of carbon melts, b) the crystallization from carbon-saturated iron melts, and c) the decomposition of aluminum carbide. Fairly good crystals of graphite were obtained by the solidification of the carbon melts, but the size of the crystals was very small. By the crystallization from a carbon-saturated iron melt crystals of 30 mm across and 0.06 mm thick were obtained and by the decomposition of aluminum carbide flaky crystals of graphite 2〜3 mm across deposited from vapour phase.
