Question

why carbon dioxide is called fixed air

Answer 1

Carbon dioxide was the first gas to be distinguished from ordinary air, perhaps because it is so intimately connected with the cycles of plant and animal life. Carbon dioxide is released during respiration and combustion. When plants store energy in the form of food, they use up carbon dioxide.The properties of carbon dioxide were further studied in the 1750s by the Scottish physician Joseph Black. He found that limestone(calcium carbonate) could be heated or treated with acids to yield a gas he called "fixed air." He observed that the fixed air was denser than air and supported neither flame nor animal life.