What is Quicklime?

Quicklime is a caustic compound known by its chemical name calcium oxide (CaO). It appears as a white powder when cold, and yellow when heated. Quicklime is produced by heating naturally-occurring limestone rock, which contains calcium carbonate. Being highly alkaline in nature, quicklime tends to react with the acidic carbon dioxide present in the atmosphere to again form calcium carbonate, or limestone, from which it was produced in the first place.