Calcium oxide (CaO), more commonly known as lime or quicklime, has been studied by scholars as far back as the pre-Christian era. In his book Historia Naturalis, for example, Pliny the Elder discussed the preparation, properties, and uses of lime. Probably the first scientific paper on the substance was Dr. Joseph Black's "Experiments Upon Magnesia, Alba, Quick-lime, and Some Other Alkaline Substances," written in 1755.

Lime does not occur naturally since it reacts so readily with water (to form hydrated lime) and carbon dioxide (to form limestone). It is synthetically produced in very large quantities by the heating of limestone. For many years, calcium oxide has ranked among the top 10 chemicals in the United States in terms of production. Other common names by which the compound is known include burnt lime, unslaked lime, fluxing lime, and calx.

In its pure form, calcium oxide occurs as white crystals, white or...