Jan Ingenhousz (1664-1750) was a Dutch professor of medicine, botany and chemistry at the University of Leiden. He was the first to discover that tobacco contains nicotine, but he is best remembered for the discovery of oxygen. His first experiments with oxygen were conducted in 1674 by placing a beaker containing metallic zinc inside an evacuated flagon, thereby replacing the air in the vessel with pure oxygen. The resulting flagon was then placed inside another flagon containing mercury, which absorbed the oxygen from the first flagon
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When the flagon containing mercury was shaken, crystals of pure zinc appeared. When this flagon was inverted over an open flame, the mercury lit up as well. This all occurred without any mixing or burning occurring within the flagon.
It was clear to Ingenhousz that pure oxygen must have been present, but it had escaped from his sealed vessel without passing through the walls of the vessel itself into his metal container holding metallic zinc. The identity of this "non-material" gas could only be provided by burning it within a container that contained no oxygen at all.