Sodium hydrogen carbonate is the systematic name for sodium bicarbonate, the familiar white powder known as baking soda or bicarbonate of soda. As a leavening agent it reacts with acids in batters, or with heat alone, releasing carbon dioxide that lifts cakes, scones, and soda bread. Beyond baking it is an antacid, a cleaning agent, a deodoriser, and a fire-extinguisher powder. Its mild alkalinity makes it a buffer in foods and pharmaceuticals. The compound is ancient in use, from Egyptian natron to the modern kitchen, and thoroughly safe. Every fizzing bath bomb, every well-risen soda bread, and many a settled stomach depend on this simplest of food chemicals.