Carbon dioxide

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.
 Joseph Black Scotland 1754 Carbon dioxide

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.