Hydrogen cyanide

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A clear, colorless gas or liquid that smells faintly of almonds. Hydrogen cyanide is usually sold as a 2-10% aqueous solution of hydrocyanic acid. Hydrogen cyanide has been used in the past as a fast-acting disinfectant and fumigant. However, it is on a DO NOT USE list of museum fumigants because of its dangerous toxicity and because it can tarnish metals and leave a slight odor on ethnographic materials (Zycherman and Schrock 1988). Hydrogen cyanide is also used in photographic and electroplating solutions as well as in the manufacture of acrylic polymers, dyes, and chelating agents.

Synonyms and Related Terms

HCN; prussic acid; hydrocyanic acid; formonitrile; Aeor; Discoids; Cyanogas; Cyclon


  • Extremely toxic by inhalation, ingestion and skin absorption. LD50=6.4 mg/kg.
  • It is one of the fastest acting toxins known. Antidotes are sodium nitrite and sodium thiosulfate.
  • Flammable and explosive.
  • Can discolor and react with metals at RH above 30%.
  • Airgas: SDS

Physical and Chemical Properties

Miscible with water, ethanol. Slightly soluble in ether.

Composition HCN
CAS 74-90-8
Melting Point -13.4 C
Molecular Weight mol. wt. = 27.03
Boiling Point 25.6 C

Resources and Citations

  • Lynda A. Zycherman, J.Richard Schrock, A Guide to Museum Pest Control, FAIC and Association of Systematics Collections, Washington DC, 1988
  • L. Goldberg, A History Of Pest Control Measures In The Anthropology Collections, National Museum Of Natural History, Smithsonian Institution, JAIC (35):23-43, 1996
  • Random House, Webster's Encyclopedic Unabridged Dictionary of the English Language, Grammercy Book, New York, 1997
  • The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998
  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • The Merck Index, Martha Windholz (ed.), Merck Research Labs, Rahway NJ, 10th edition, 1983 Comment: entry 4836
  • G.S.Brady, Materials Handbook, McGraw-Hill Book Co., New York, 1971 Comment: p. 404
  • Hermann Kuhn, Conservation and Restoration of Works of Art and Antiquities, Butterworths, London, 1986
  • Stephen R. Edwards, Bruce M. Bell, Mary Elizabeth King, Pest Control in Museums: a Status Report 1980, Association of Sytematics Collections, Washington DC, 1980
  • Michael McCann, Artist Beware, Watson-Guptill Publications, New York City, 1979
  • G.Caneva, M.P.Nugari, O.Salvadori, Biology in the Conservation of Works of Art, ICCROM, Rome, 1991