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a chemical element, atomic number 1, atomic weight 1.00797. (See Appendix 6.) It exists as the mass 1 isotope (protium, or light or ordinary hydrogen), mass 2 isotope (deuterium, heavy hydrogen), and mass 3 isotope (tritium).
hydrogen cyanide an extremely poisonous colorless liquid or gas, HCN, a decomposition product of various naturally occurring glycosides and a common cause of cyanide poisoning. Inhalation of the gas can cause death within a minute. Called also hydrocyanic acid.
heavy hydrogen deuterium.
hydrogen ion concentration the degree of concentration of hydrogen ions (the acid element) in a solution. Its symbol is pH, and it expresses the degree to which a solution is acidic or alkaline. The pH range extends from 0 to 14, pH 7 being neutral, a pH of less than 7 indicating acidity, and one above 7 indicating alkalinity. See also acid-base balance.
hydrogen peroxide H2O2, an antiseptic with a mildly antibacterial action. A 3 per cent solution foams on touching skin or mucous membrane and appears to have a mechanical cleansing action.
hydrogen sulfide H2S, a poisonous gas with an offensive smell, released from decaying organic material, natural gas, petroleum, and sulfur deposits, and sometimes used as a chemical reagent.
hy·dro·cy·an·ic ac·id (HCN),(hī'drō-sī-an'ik as'id),
HCN; A colorless, toxic liquid, with the odor of bitter almonds, present in bitter almonds (amygdalin), the stones of peaches, plums, and other drupes, and laurel leaves; inhalation of 300 ppm causes death.
hy·dro·gen cy·a·nide(HCN) (hī'drō-jen sī'ăn-īd)
A highly toxic cellular asphyxiant, HCN, used as a fumigant and also as a chemical-warfare agent. Its NATO code is AC.