The Protium reference article from the English Wikipedia on 24-Jul-2004
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Protium

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In chemistry, protium is the most common isotope of the element hydrogen that has one proton and no neutrons. It is denoted by the symbol ¹H.

Other isotopes of hydrogen are the rarer deuterium and the radioactive isotope tritium.

In biology, Protium is a genus of chiefly tropical American trees having fragrant wood and yielding gum elemi.