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.
3. When flour or finely ground meal is to be mixed with a hot liquid, separate the particles before they reach the hot liquid, or gummy lumps with raw centers will be formed. This separation of the particles of flour or meal can be accomplished by mixing the flour or meal with enough cold liquid to make a mixture as thin as cream, or by combining them with sugar or with fat before mixing them with the hot liquid. Lumpy gravies, sauces, mushes and puddings are caused by a failure to observe these precautions.
4. A double boiler is the best utensil to use in cooking cereals, mushes and starchy sauces because it does away with the danger of sticking and burning. The water in the lower part of the boiler should be boiling.