Up to now, carbon dioxide had only been detected as a product of combustion or fermentation. Black described how to create a gas by heating limestone, calling it "fixed air" because it could be fixed back into a solid by combining with lime. He also found that calcium oxide turned into calcium carbonate naturally in the air, so there must be carbon dioxide in the atmosphere.
A visual chronology of Asimov's ~1500 scientific inventions and discoveries.
