We Americans were the first to make breads and cakes rise by chemical means, thus saving ourselves the wait for yeast to grow. In the late 18th century, we started leavening dough with pearl ash (potassium carbonate), a powder derived from wood ashes. It would produce carbon dioxide bubbles in the dough if there were an acid component, which could easily be supplied by including vinegar or sour milk in the recipe. By the early 19th century, we were using a more refined form of pearl ash known as saleratus (sal aeratus, aerated salt).
In the 1840s, “saleratus” came to mean the familiar modern baking soda (sodium bicarbonate). It was immensely popular. American general stores sold it out of barrels, the way they sold sugar and flour; cowboys lived mostly on beans and saleratus biscuits. Finally, for even greater convenience, we devised the all-in-one package of baking powder, which contains a chemical to produce the acidity that makes the baking soda bubble.
These days, health foodies are in love with yeast-leavened bread--risen as long as possible, because the process is believed to make nutrients more available. In the 19th century, they felt exactly the other way: They considered leavened dough, with all those microscopic organisms living in it, to be rotting. Anyway, a lot of 19th century dietary reformers were prohibitionists and opposed to even the minuscule amount of alcohol produced in fermentation.
Not that everybody approved of saleratus. In one of her later novels, Harriet Beecher Stowe sneered at baked goods “got up with the acrid poison of saleratus.” You can’t please everybody.