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What is hydrogen?  Why is hydrogen?  In History  In Chemistry  The Atom
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The Perodic Table Of The Elememts

He published a paper ("New experiments touching the relation betwixt flame and air") in 1671 in which he described the reaction between iron filings and dilute acids which results in the evolution of gaseous hydrogen ("inflammable solution of Mars" [iron]). However it was only much later that it was recognized as an element by Henry Cavendish (1731-1810; English chemist and physicist; independently discovered nitrogen as well) in 1766 when he collected it over mercury and described it as "inflammable air from metals". Cavendish described accurately hydrogen's properties but thought  erroneously that the gas originated from the metal rather than from the acid. Hydrogen was named by Lavoisier. Deuterium gas (2H2, often written D2), made up from deuterium, a heavy isotope of hydrogen, was discovered in 1931 by Harold Urey, a  professor of chemistry at Chicago and California (both USA). 

And nowadays , there is a  Strange Matter cartoon  included by kind permission of Nick Kim at the University of Waikato, New Zealand.