Experiments Upon Magnesia Alba, Quicklime, and Some Other Alcaline Substances

In his work "Experiments Upon Magnesia Alba, Quicklime, and Some Other Alcaline Substances," Joseph Black investigated the properties of alkaline substances, particularly magnesia alba (now known as magnesium carbonate). Black's experiments demonstrated that magnesia alba, when heated, lost weight due to the release of a gas he termed "fixed air," which is now known as carbon dioxide. He also showed that this gas could be reintroduced to the heated substance (magnesia usta, or magnesium oxide) to recreate the original magnesia alba.12

Black's research extended to quicklime (calcium oxide), showing that it also released "fixed air" when heated and that this gas was contained within alkaline substances. This groundbreaking work established that gases could be distinct chemical substances and not merely variations of atmospheric air, paving the way for the characterization of other gases.234