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The Collaborative International Dictionary of English v.0.48 (gcide)

Hydrogen \Hy"dro*gen\, n. [Hydro-, 1 -gen: cf. F.
hydrog[`e]ne. So called because water is generated by its
combustion. See {Hydra}.] (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.
[1913 Webster]

Note: Although a gas, hydrogen is chemically similar to the
metals in its nature, having the properties of a weak
base. It is, in all acids, the base which is replaced
by metals and basic radicals to form salts. Like all
other gases, it is condensed by great cold and pressure
to a liquid which freezes and solidifies by its own
evaporation. It is absorbed in large quantities by
certain metals (esp. palladium), forming alloy-like
compounds; hence, in view of quasi-metallic nature, it
is sometimes called {hydrogenium}. It is the typical
reducing agent, as opposed to oxidizers, as oxygen,
chlorine, etc.
[1913 Webster]

{Bicarbureted hydrogen}, an old name for ethylene.

{Carbureted hydrogen gas}. See under {Carbureted}.

{Hydrogen dioxide}, 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}.

{Hydrogen oxide}, a chemical name for water, H?O.

{Hydrogen sulphide}, 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}.
[1913 Webster]