Two high pressure devices, the opposed anvil and the tetrahedral anvil, have been used for studying chemical reactions at high pressures and high temperatures. The effect of pressure on the thermal decomposition of potassium chlorate and mercuric oxide has been determined experimentally. New cubic mercury and cadmium metaborates were isolated and studied. Group III superoxides have been synthesized under high pressures and their properties have been investigated by x-ray, infrared, electron spin resonance and chemical methods. Three new high pressure forms of LiMO2(M = B, Al and Ga)-compounds have been synthesized and identified. It is found that y-LiB02 and y-LiA10 could be synthesized directly by reacting lithium peroxide with boric oxide and aluminum oxide respectively.