Black realized that when chalk or marble was heated, a gas which he called fixed air was released. He was able to collect the gas, which we know as carbon dioxide, and to study its properties. He was also able to show that carbon dioxide was a normal constituent of the air because quicklime was changed into ordinary chalk, albeit tardily, by exposure to air. This was the first atmospheric gas to be isolated and described. The discovery heralded the dawn of a new era in chemical investigation, and so Black is often given the title-Father of Pneumatic Chemistry.