This section is from the book "Practical Dietetics With Special Reference To Diet In Disease", by William Gilman Thompson. Also available from Amazon: Practical Dietetics with Special Reference to Diet in Disease.
Carbonic-acid gas may be developed in bread by the action of baking powders. These powders are very extensively employed, and "a conservative estimate of the quantity of baking powder used in the United States each year places the figure considerably above 50,000,000 pounds " (Clark).
There has, however, been much argument in regard to their wholesomeness, and elaborate researches in chemistry and the physiology of digestion have been conducted to determine whether or not the continued use of these ingredients in bread is injurious. The so-called baking powders are manufactured by the combination of many different ingredients, such as sodium carbonate with tartaric acid, the acid phosphate of lime with sodium carbonate and potassium chloride (Liebig-Horsford), or a combination may be used of ammonium carbonate with hydrochloric acid. It is claimed by the advocates of the use of baking powders that they possess many acjvantages, such as the fact that the bread rises quicker, and that although fermentation does not occur, the bread is more porous, and hence more digestible, and that its taste is not impaired. On the other hand, it is argued that such bread is practically less wholesome, and that its continued use, from the introduction of so many chemicals, especially when ammonium carbonate is employed, proves irritating to the stomach and may excite dyspepsia and gastric catarrh.
Even when not used for the making of bread these baking powders are often employed in the preparation of various forms of cake where lightness and quickness in making are important features.
Baking powder when pure should consist only of cream of tartar (acid tartrate of potash, obtained as a precipitate in the casks in which wine is made) and soda, with a little flour added, and should be free from alum, ammonia, etc. Mixed with water and dough, the soda is split by the acid tartrate, liberating carbonic-acid gas. Alum is sometimes used in baking powders with soda. Its action is less reliable, and in large quantities it is astringent and injurious to digestion.