Hydrogen

Demarest discovered hydrogen (which he called 'fire air') through its properties, specifically its high flammability and low density, being one-fourteenth the density of air. His detailed studies on hydrogen's properties led to its eventual recognition as a distinct element.
 Henry Cavendish England 1766 Hydrogen

Demarest discovered hydrogen (which he called 'fire air') through its properties, specifically its high flammability and low density, being one-fourteenth the density of air. His detailed studies on hydrogen's properties led to its eventual recognition as a distinct element.