This section is from the book "The American Woman's Cook Book", by Ruth Berolzheimer. Also available from Amazon: The Domestic Arts Edition of the American Woman's Cook Book.
Sugar - Fine grained granulated sugar is the standard sugar for cake. A coarse grained sugar may produce a coarse grained cake with a hard crust. Light brown or dark brown sugar is preferred by most people for fruit cake or any dark cake. Brown sugar is lighter and more moist than granulated and when it is used instead of granulated sugar the substitution should be weight for weight, not measure for measure.
Shortening - Any fat that has a mild flavor may be used for the shortening in cake. Butter is the first choice with many cooks because of its flavor, but it is the most expensive of fats. Tasteless vegetable or animal oils or hardened fats produce perfect results, aside from the flavor. Since these fats are unsalted the amount of salt should be increased by one-half.
Hard fats should be creamed with the sugar. If they are melted and added while hot, the cake is likely to be tough. If melted fat is called for, it should be cooled before it is added.
Eggs - Eggs for cake need not be newly laid, but they should be of good quality, free from taint and fresh enough to beat up well. Two yolks or two whites may be used instead of one whole egg, or a yolk may be substituted for a white or the other way around. The substitution of yolks for whites or vice versa makes a difference in the color and to some extent in the texture of the cake. In recipes calling for egg whites alone or for more whites than yolks, the number of whites cannot be reduced without changing the texture of the cake. If an egg white is used instead of a yolk, one teaspoon of shortening should be added. When fewer whole eggs are to be used than a recipe calls for, add one-half teaspoon of baking powder instead of each egg omitted, after the first one. Eggs improve the quality of the texture of batters, and while a fairly good plain cake can be made with only one egg, additional eggs give a lighter, more delicate texture, improve the flavor and produce a smoother crust.
Flour - In the cake recipes given in this book, cake flour has been used. Cake flour has a low gluten content and therefore makes a finer textured cake. Although cake flour is preferred for cakemaking, successful cakes are made with all-purpose flour. If all-purpose flour is used for cake flour, reduce the amount of flour used by 2 tablespoons per cup of flour called for and do not beat the batter as long as when using cake flour. Always sift flour before measuring. Fill cup lightly. Resifting with dry ingredients as directed.
Leavening Agents - The most usual leavening agents in cakemaking are eggs and baking powder. When 1 egg is omitted from a recipe the baking powder should be increased by 1/2 teaspoon. If the liquid used is sour milk or cream, use 1/2 teaspoon baking soda for each cup of liquid. Then decrease baking powder slightly. It is best to sift the baking soda with the dry ingredients. If the soda is dissolved in the sour milk it must be added to the mixture immediately or some of the gas to be used in leavening will be lost.
Flavorings - A cake shortened entirely with good butter needs no additional flavoring though most people add some flavoring extract. Vanilla and lemon extracts are used more commonly than others, but almond, orange, pineapple, and rose give a variety in flavors. Very often the juices of fresh fruit such as lemon or orange, or the grated peel or rind, are used in certain types of cake. Too much flavoring is a common mistake. The amount given in recipes is for an extract of average strength. Where an extract of greater strength is used the amount should be decreased.