The creation of shelf-stable chemical combinations of sodium bicarbonate and cream of tartar is seen as marking the true introduction of baking powder. Although cooks had used both sodium bicarbonate and cream of tartar in recipes, they had to purchase the ingredients individually and store them separately to prevent them from spoiling or reacting prematurely. As chemists developed more uniform constituents, they also began to experiment with ways of combining them. In the mid-late 1800s, chemists introduced the first modern baking powders.