The term "boiling" is often used erroneously in cookery. The expressions "the teakettle boils," "the rice is boiling," "boiled beef," etc., are all good illustrations of the rhetorical figure metonymy, but they are practically incorrect. In all cases it is only the water or liquid which boils. No solid can boil until first changed to a liquid. Solids become liquid at the melting-point. Liquids take the form of steam or vapor at the boiling-point. Boiling is the conversion of a liquid into steam by the application of heat sufficient to cause ebullition, or agitation of its surface. Boiling, therefore, as applied to the cooking of solids, is heating or cooking in a boiling liquid. It is one of the most generally used, and abused, forms of cooking. Boiling water, which is really cooked water, is the liquid usually employed. Water, as it is heated from below, expands into vapor. The air of the water and the steam shoot up in the form of bubbles; as they come in contact with the cold water near the surface, the bubbles collapse, the steam is condensed and descends with the cold water, making a double set of currents, which causes quite a commotion among the particles. As the whole body of water becomes hotter, these bubbles of steam rise higher and higher before collapsing, and occasion the sound which we call the "singing of the kettle." When the water is sufficiently heated, they rise and break at the surface, causing more or less agitation, according to the rapidity with which they are formed. Water is scalding hot at 150°, or when the hand cannot be borne in it. Water simmers when the bubbles all collapse beneath the surface, and the steam is condensed to water again, or at 185°. Water boils when the bubbles rise to the surface, and the steam is thrown off, as at 212°. When this boiling-point is reached, the heat escapes with the steam; and all the fire in the world cannot make the water any hotter, so long as the steam escapes. If the fire be very fierce, so that these bubbles are formed and expelled rapidly, and the water boils over, the water is no hotter; it only evaporates or boils away faster, and can only be made hotter by confining the steam, which in ordinary kettles is impossible, owing to the enormous expansive force of the steam. With a few exceptions it is a waste of fuel, time, and material to keep the water boiling at such a galloping rate that the cover has to be lifted to prevent boiling over.

A kettle should never be quite full, as the water expands in heating, and, in boiling over, makes needless work and injures the stove. Water will boil more quickly in a kettle with a rough surface than in one with a smooth surface, as the water adheres to a smooth surface with greater force, and this force or attraction must be overcome before boiling takes place. Small, clean gravel is sometimes kept in a smooth kettle to facilitate the boiling.

Water boils at a higher temperature when there is sugar, or salt, or anything in it to increase its density. It takes longer for it to boil; but it is hotter, when that point is reached. No one who has been burned by boiling syrup ever doubted this fact. Fresh water boils at 212°; salt water, at 224°. If we put salt with the water in the lower part of a double boiler, a greater degree of heat is obtained by which to cook the articles in the top.

Water boils at a lower temperature, that is, more quickly, when the pressure of the air upon the water is diminished. Before a rain the pressure of the air is lessened, because the air when filled with vapor is lighter. Observing housekeepers have often noticed how quickly things burn at such a time, and foretell a rain by the rapidity with which water evaporates.

The pressure of the air is less the higher we ascend above the level of the sea, since we leave much of the air below us. Cooking in boiling water requires a much longer time in mountainous regions; for the water boils so quickly that it holds less heat than in lower altitudes, where it is subject to greater pressure. Water, in boiling, loses the air or gases which give it a fresh taste and sparkling appearance. It becomes flat and tasteless. If there be any impurity in water, boiling or cooking will destroy it. Then, by cooling, and exposing to pure air again, it becomes aerated and palatable. But water for cooking, unless there are impurities to be removed, should be used when freshly boiled. This is especially important in making tea and coffee.

Soft water should be used in boiling where the object is to soften the texture, and extract the soluble parts, as in soups, broths, tea, and coffee. Hard water, or soft water salted, is better where we wish to preserve the articles whole, and retain the soluble and flavoring principles, as in most green vegetables. Beans or dried peas, which contain casein or vegetable albumen in large proportion, should be cooked in soft water, as the lime in hard water hardens the casein, and prevents the vegetables from becoming soft.

In cooking meat, fish, and vegetables in water, we should remember these two facts: -

Cold water draws out the albuminous juices, softens the fibres and gelatinous portions of meat, and holds them in solution. It draws out starch, but does not unite with it.

Boiling water hardens and toughens albumen and fibrine, bursts the starch grains, and is absorbed by the swelling starch.

Meat is cooked in water for three distinct purposes: -

First. To keep the nutriment within the meat, as in what is usually called boiled meat. To do this, we leave the meat whole, that only a little surface may be exposed. Plunge it into boiling salted water, and keep it there for five or ten minutes; this hardens the albumen over the entire surface, and makes a coating through which the juices cannot escape. Then move the kettle where the water will simmer slowly. See that the cover fits tightly, to keep in the steam. The water should be salted to raise the boiling-point, and increase the density of the water, and thus prevent the escape of the juices. A small amount of the albumen in the outer surface will be dissolved and rise as scum. This should be removed, or it will settle on the meat and render it uninviting in appearance. If the meat be put in the kettle with the bones uppermost, then the scum will not settle on the meat. In turning the meat do not pierce into it to let the juices escape. It will take a longer time to cook in this way, but the fibrine will be softened, and the meat made more tender and of better flavor, than when kept boiling furiously.