from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun A colorless, highly flammable element, that occurs as a diatomic molecule, H2, the lightest of all gases and the most abundant element in the universe, used in the production of synthetic ammonia and methanol, in petroleum refining, in the hydrogenation of organic materials, as a reducing atmosphere, in oxyhydrogen torches, in cryogenic research, and in rocket fuels. Atomic number 1; atomic weight 1.00794; melting point −259.1°C; boiling point −252.8°C; density at 0°C 0.08988 gram per liter; valence 1. cross-reference: Periodic Table.

from The Century Dictionary.

  • noun Hydrogen compounds with strongly electronegative elements or radicals, easily exchanging hydrogen for strongly electropositive elements or radicals to form salts, are the same as acids: as hydrogen chlorid (hydrochloric acid), hydrogen sulphate (sulphuric acid), etc.
  • noun Chemical symbol, H. One of the elementary substances, existing as a colorless, tasteless, and inodorous gas.
  • noun H2S, a colorless inflammable gas having a sweetish taste and an exceedingly fetid smell resembling rotten eggs. It is extremely poisonous when inhaled. It has feeble acid properties, and its compounds with bases are called sulphids. It occurs in the emanations of volcanoes, and is evolved when animal or vegetable tissue containing sulphur decays. It also occurs in mineral springs, being liberated by the reduction of gypsum or other sulphates through the action of a microbe.

from the GNU version of the Collaborative International Dictionary of English.

  • noun (Chem.) A gaseous element, colorless, tasteless, and odorless, the lightest known substance, being fourteen and a half times lighter than air (hence its use in filling balloons), and over eleven thousand times lighter than water. It is very abundant, being an ingredient of water and of many other substances, especially those of animal or vegetable origin. It may by produced in many ways, but is chiefly obtained by the action of acids (as sulphuric) on metals, as zinc, iron, etc. It is very inflammable, and is an ingredient of coal gas and water gas. It is standard of chemical equivalents or combining weights, and also of valence, being the typical monad. Symbol H. Atomic weight 1.
  • noun an old name for ethylene.
  • noun See under Carbureted.
  • noun a thick, colorless liquid, H2O2, resembling water, but having a bitter, sour taste, produced by the action of acids on barium peroxide. It decomposes into water and oxygen, and is manufactured in large quantities for an oxidizing and bleaching agent. Called also oxygenated water.
  • noun a chemical name for water, H�O.
  • noun a colorless inflammable gas, H2S, having the characteristic odor of bad eggs, and found in many mineral springs. It is produced by the action of acids on metallic sulphides, and is an important chemical reagent. Called also sulphureted hydrogen.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun The lightest chemical element (symbol H) with an atomic number of 1 and atomic weight of 1.00794.
  • noun Molecular hydrogen (H2), a colourless, odourless and flammable gas at room temperature.
  • noun An atom of the element.
  • noun A sample of the element.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • noun a nonmetallic univalent element that is normally a colorless and odorless highly flammable diatomic gas; the simplest and lightest and most abundant element in the universe


from The American Heritage® Dictionary of the English Language, 4th Edition

[French hydrogène : Greek hudro-, hydro- + French -gène, -gen.]

from Wiktionary, Creative Commons Attribution/Share-Alike License

From French hydrogène, coined by Louis-Bernard Guyton de Morveau, from Ancient Greek ὕδωρ (hudōr, "water") + γεννάω (gennaō, "I bring forth").


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  • ~ New 'biofuel cell' produces electricity from hydrogen in plain air -- "A pioneering “biofuel cell” that produces electricity from ordinary air spiked with small amounts of hydrogen offers significant potential as an inexpensive and renewable alternative to the costly platinum-based fuel cells that have dominated discussion about the “hydrogen economy” of the future, British scientists reported here today."

    Speedlinking 3/27/07

  • But if we consider hydrogen as a gasiform metal, we naturally arrive at the conclusion that _water is the hydroxide of this gasiform metal_, that is _hydrogen hydroxide_, while gaseous hydrochloric and hydrosulphuric acids would be looked upon as respectively the chloride and the sulphide of the metal hydrogen.

    Scientific American Supplement No. 822, October 3, 1891

  • Carbon also escapes into the air, combined with hydrogen, in the form of _carburetted hydrogen_ or _marsh-gas_ (CH_4), a product of the decomposition of organic matter in the presence of a large quantity of water.

    Manures and the principles of manuring

  • I believe it was linzloo08 who said that, in referencing the fact that the sun will stop shining when the hydrogen is all gone.

    Think Progress » Sarah Palin calls global warming studies ‘snake oil science.’

  • We already know that the poles of the Moon contain elevated hydrogen content (the rare element on the Moon); this hydrogen is there regardless of its physical form, either as water ice or as solar wind protons.

    Back to the Moon We Go - NASA Watch

  • This is the pipe through which we convey this particular gas, which we call hydrogen, and which you shall know all about the next time we meet.

    The Chemical History of a Candle

  • The atoms of what we call hydrogen or oxygen may well turn out to be worlds, as the stars are which make atoms for astronomy.

    The Life of Reason

  • "This is a result of what we call the hydrogen effect," says Patrik Fors, who will defend his thesis in nuclear chemistry at Chalmers on Friday. - latest science and technology news stories

  • "This is a result of what we call the hydrogen effect," says Patrik Fors, who will defend his thesis in nuclear chemistry at Chalmers on Friday.

    EurekAlert! - Breaking News

  • As everyone has pointed out, hydrogen is a very tricky substance to store, and that is why one of the cheaper methods is to use fossil fuels.

    Hydrogen Cars, Arnold Kling | EconLog | Library of Economics and Liberty


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    December 16, 2007