Man's Conquest of Substances
Salt is by all odds the most important sodium compound. Next to it come the so-called carbonates: first, sodium carbonate, which is already familiar to us as washing soda; and second, sodium bicarbonate, which is an ingredient of baking powders. These are both obtained from sodium chloride by relatively simple means; that is, by treating salt with the base, ammonia, and with carbon dioxide.
Washing soda has already been discussed. Since baking powders in some form are used in almost all homes for the raising of cake and pastry dough, it is essential that their helpful and harmful qualities be clearly understood.
The raising of dough by means of baking soda - bicarbonate of soda - is a very simple process. When soda is heated, it gives off carbon dioxide gas; you can easily prove this for yourself by burning a little soda in a test tube, and testing the escaping gas in a test tube of limewater. When flour and water alone are kneaded and baked in loaves, the result is a mass so compact and hard that human teeth are almost powerless to crush and chew it. The problem is to separate the mass of dough or, in other words, to cause it to rise and lighten. This can be done by mixing a little soda in the flour, because the heat of the oven causes the soda to give off bubbles of gas, and these in expanding make the heavy mass slightly porous. Bread is never lightened with soda because the amount of gas thus given off is too small to convert heavy compact bread dough into a spongy mass; but biscuit and cake, being by nature less compact and heavy, are sufficiently lightened by the gas given off from soda.
But there is one great objection to the use of soda alone as a leavening agent. After baking soda has lost its carbon dioxide gas, it is no longer baking soda, but is transformed into its relative, washing soda, which has a disagreeable taste and is by no means desirable for the stomach.
Man's knowledge of chemicals and their effect on each other has enabled him to overcome this difficulty and, at the same time, to retain the leavening effect of the baking soda.