Baking-powders are artificial leavens. What nature does through the growth of yeast, humankind seek to bring about through baking-powders. The endeavor is to produce the rising effect of yeast by incorporating in mixtures to be raised such substances as will give off carbon dioxid gas when they are united. Baking-powders as commercially produced and practically used are the result of this effort.

They all contain carbon dioxid in some combination. Soda (sodium bicarbonate) and an acid when brought together give off carbon dioxid. This is the general combination of substances used in baking-powders. To prevent the escape of the carbon dioxid until it is needed, the soda is mixed with starch. The acid substance cannot then unite chemically with the soda at once when these are brought together.

The starch so used is called a filler. While dry the action between the soda and acid is prevented; hence the necessity of keeping baking-powder in closed tin cans or glass jars. When the baking-powder is mixed with a flour-mixture it is then moistened. This causes the soda and acid to combine chemically and give off the gas that expands and raises the mixture, making it porous and light, thereby digestible.

The time a baking-powder takes to form the gas that raises mixtures depends upon the proportions of its ingredients. If the proportion of the "filler" is large as compared with that of the soda-acid combination, then the powder acts slowly. Otherwise it is a quick rising-agent. The commercial value of a baking-powder is based upon its rising quality. The one with the most filler will cost least. The starch filler varies from l/6 to 1/2 the weight of baking-powders as purchased.

In principle of action all baking-powders are alike, that is, they produce the necessary gas.