Joseph Louis Gay-Lussac
In 1809, Joseph Louis Gay-Lussac and Louis-Jacques Thénard tried to decompose "dephlogisticated muriatic acid air" by reacting it with charcoal to release the free element "muriaticum" (and carbon dioxide). They did not succeed and published a report in which they considered the possibility that "dephlogisticated muriatic acid air" is an element, but were not convinced.