In cooking some kinds of food, milk is used in the place of water. Milk contains water, sugar, salts, fat, albumen, and casein.

After it stands awhile, the fat separates and rises as cream. The sugar and salts are dissolved in the water of the milk. The casein is dissolved in fresh milk, but when the milk becomes old, and sours, it separates from the watery part and forms a thick mass which we call curd. This curd is made into cheese. Now as milk contains all these substances it is thicker than water, and when we boil it, it adheres to the pan and burns quickly. The bubbles of water in the milk, as they change into steam, rise rapidly, the albumen hardens, and forms a skin-like coating; as this skin is thick and tenacious, owing to the other substances in the milk, these bubbles do not break quickly at the surface as clear water bubbles do, but stretch and climb one upon another till they run over the edge of the pan. By heating milk in a double boiler we avoid the danger of its burning or running over. When the whole surface is covered with air bubbles, - not steam bubbles, - the milk is hot enough, though not actually boiling. The temperature of boiling milk is slightly higher than that of boiling water, and it will not boil over boiling water.

Rice may be cooked in boiling milk as well as in water, but milk being the thicker, a little more will be required than of water.

Eggs are also cooked in hot milk. When we break an egg, we find the white is soft and without form, and the yolk seems round and firmer than the white ; but if we break the film or membrane on the outside of the yolk we find that it, too, is soft and liquid. By beating, we can mix the yolk and white, and be unable to distinguish them. Sometimes we want to use the two parts separately, and it is quite an art to break and divide an egg, and not mix the yolk with the white. When eggs are cooked in milk, the albumen in the egg thickens, and if cooked slightly, and stirred constantly, forms a smooth, soft, creamy mass. If cooked longer, and without stirring, it becomes thick and solid; but if cooked too long the casein and albumen become quite hard, and separate from the watery part, or the mass curdles.

Eggs cooked in milk, and seasoned with salt, pepper, and butter, are called poached eggs. When they are sweetened we call the mixture a custard.

When eggs are eaten raw, or cooked in any way in which the result is to be a smooth, soft mass, the thick white substance uniting the yolk and white should be removed before cooking, unless the cooked mixture is to be strained, as in soft custard. This substance hardens into a lump, and it is unpleasant to find it in what would otherwise be a smooth mass. In eggs cooked in the shell, or cooked hard as in cake, it is not perceptible.