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Hydrogen. The first chemical element in the periodic table. It has the atomic symbol H, atomic number 1, and atomic weight 1. It exists, under normal conditions, as a colorless, odorless, tasteless, diatomic gas. Hydrogen ions are PROTONS. Besides the common H1 isotope, hydrogen exists as the stable isotope DEUTERIUM and the unstable, radioactive isotope TRITIUM.

A colorless, gaseous, inflammable substance, which becomes liquid under great pressure, and is the lightest element yet known, much lighter than air; when combined with oxygen it produces water.

An odorless, colorless, tasteless element, gaseous at ordinary temperatures and pressure; symbol H, atomic weight 1. It is the lightest known substance, and the weight of one of its atoms is the unit of atomic weights. It is readily replaceable in many compounds by other elements or radicals, and this substitution of the hydrogen atoms in an acid forms a salt.

A light gas, producing water upon oxidation.

A gas which in combination with oxygen produces water, an elementary gaseous substance, the lightest of all known substances, and very inflammable.

A gas, one of the elements of water, and the lightest substance known.

Hydrogenous.

A colorless, odorless, tasteless, gaseous element, the lightest substance known.

A highly inflammable gas, constituting one of the elements of water, and the lightest of aeriform bodies.

A gaseous body, and the lightest of all known bodies-called also inflammable air, and producing water when combined with oxygen.

This gas, when breathed, proves fatal from containing no oxygen. When diluted with two-thirds of atmospheric air, it occasions some diminution of muscular power and sensibility, and a reduction of the force of the circulation. It has been respired in catarrh, haemoptysis, and phthisis.

Light inflammable gaseous element; symbol H.

A non-metallic gaseous element. It is one of the components of water and of many other inorganic substances and is a constant constituent of organic compounds. It is a colorless, tasteless, odorless, inflammable gas, and is the lightest substance known, its sp. gr. (air= 1) being 0,0695 and to water as 1 to 11,160. Its density is, accordingly, selected as the unity of density for gases. Under a very low temperature, combined with the application of very great pressure, it is liquefied, forming a bluish, opaque liquid. In composition, it forms the essential element in the class of compounds called acids, which are hence denominated salts of hydrogen, and, united with carbon, it forms the important class of organic compounds called hydrocarbons. In compounds it never replaces more than one atom of another element, and hence its combining power is regarded as a unit, to which that of other elements is referred, and their quantivalence is measured by the number of atoms of hydrogen which they can replace. Atomic weight 1.008 (O= 16.0). Chemical symbol H.

n. [Greek] An inflammable colourless gas of extreme lightness, which constitutes one of the elements of water, and of all organized bodies.