The first chemical element in the periodic table with atomic symbol H, and atomic number 1. Protium (atomic weight 1) is by far the most common hydrogen isotope. Hydrogen also exists as the stable isotope DEUTERIUM (atomic weight 2) and the radioactive isotope TRITIUM (atomic weight 3). Hydrogen forms into a diatomic molecule at room temperature and appears as a highly flammable colorless and odorless gas.
    

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James Sadler setting off on the proposed first crossing of the Irish Sea from Dublin by  balloon, 1812; with details of the hydrogen barrels and equipment. Engraving.

Hydrogen

Images

Catalogue

Hydrogen : the essential element / John S. Rigden.

Ballooning: hydrogen barrels and other equipment used in ballooning. Engraving by W. Lowry, 1803.

James Sadler setting off on the proposed first crossing of the Irish Sea from Dublin by balloon, 1812; with details of the hydrogen barrels and equipment. Engraving.

The fine structure of hydrogen and the gross structure of the physics community, 1916-26 / Helge Kragh.