Lime

"Chemically, it is the oxide of calcium, with the formula CaO. It occurs in limestone, marble and chalk as calcium carbonate, CaCO3. If these substances are heated, carbon dioxide, CO2 escapes as a gas and CaO, or quicklime, remains.Quicklime combined with the correct amount of water yields slaked lime or hydrate of lime, Ca(OH)2.

Quicklime, CaO, will unite with water in the soil to form a hydrate. If enough free water is not available, as it seldom is, the quicklime wrenches water from living organisms in the soil, such as bacteria, fungi or plant roots, usually burning them enough to bring about their death."

The Encyclopedia of Organic Gardening, Rodale 1978