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quicklime (CaO), compound of one atom of calcium and one atom of oxygen that is a white or grayish white solid produced in large quantities by roasting calcium carbonate so as to drive off carbon dioxide. At room temperature, CaO will spontaneously absorb carbon dioxide from the atmosphere, reversing the reaction. It will also absorb water, converting itself into calcium hydroxide and releasing heat. The bubbling that accompanies the reaction is the source of its...