Calcium oxide

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White, alkaline lumps. Calcium oxide is a refractory solid that becomes incandescent at temperatures near its melting point (2500C). In 1816, prior to the development of electrical lights, calcium oxide was used for bright white illumination, called limelights. Calcium oxide is primarily used in the manufacture of slaked limes for mortar, plasters, and cements. It is also used as a refractory and flux in manufacturing steel and glass. Calcium oxide is added to paper pulp for pH control and phosphate removal.

Synonyms and Related Terms

lime; quicklime; burnt lime; calx; unslaked lime; fluxing lime

Chemical structure

Calcium oxide.jpg

Other Properties

Soluble in acid. Hygroscopic. Reacts with water to form calcium hydroxide with evolution of heat.

Composition CaO
CAS 1305-78-8
Melting Point 2570
Density 3.40
Molecular Weight mol. wt. = 56.1
Boiling Point 2850

Hazards and Safety

Skin contact causes irritation and burns. Fire risk in contact with organic materials.

International Chemical Safety Card


  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • Henry Hodges, Artifacts: An Introduction to Early Materials and Technology, Ronald P. Frye, Kingston, Canada, 1988
  • Random House, Webster's Encyclopedic Unabridged Dictionary of the English Language, Grammercy Book, New York, 1997
  • The Merck Index, Martha Windholz (ed.), Merck Research Labs, Rahway NJ, 10th edition, 1983 Comment: entry 1733

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