Self-Raising Bread, Trade Card, c. 1876.
Advertising trade card touting the convenience of an early bread mix, using chemical baking powder--then a new invention--in place of the traditional, more slow-rising, yeast of the past (typically derived from the beer-making process). Baking powder was quicker, but the results were far from identical. Horsford was an early inventor-producer.
As yeasted bread moved into commercial production, and people for the most part stopped baking yeast bread at home, baking powder became the riser for so-called "light" breads, biscuits, pancakes, etc.