The lightening agents, air and steam, may be taught from the samples of baked gluten. Experiments will show how to produce the carbonic acid gas.
Experiments:
1. Put into a thick glass 1/8 tsp. of soda and 1/4 tsp. of cream of tartar. Mix, and note the result. Stir in 1/8 cup of cold water, and note the result.
2. In No. 1, use hot water in place of cold, and note the result.
3. Put 1/4 cup of sour milk in a glass. Stir into the milk 1/4 tsp. of soda, and note the result.
4. Put 1 tbsp. of molasses in a glass. Stir into the molasses a pinch of soda, and note the result.
Baking-powder:
It may now be explained that, for the sake of convenience, soda and cream of tartar may be obtained already mixed, in accurate proportions of two parts of acid to one of the soda. This mixture is known as baking-powder. As very little moisture is necessary to start the action of the powder, a little cornstarch is added to it to keep it dry. For the same reason, it should always be kept tightly covered.
Soda is made from common salt and is cheap, but the source of cream of tartar makes it expensive, so that good baking-powder cannot be low priced. If such be advertised, it is usually adulterated.
As soon as the foregoing principles of flour mixtures are understood, they should be put into practice. The lessons on cake, bread, and pastry should follow in the order named, with as much practical work in connection with each as the time will allow.