37. BOILING.--As applied to cooking, boiling means cooking foods in
boiling water. Water boils when its temperature is raised by heat to
what is commonly termed its _boiling point_. This varies with the
atmospheric pressure, but at sea level, under ordinary conditions, it is
always 212 degrees Fahrenheit. When the atmospheric pressure on the
surface of the water is lessened, boiling takes place at a lower
temperature than that mentioned, and in extremely high altitudes the
boiling point is so lowered that to cook certain foods by means of
boiling water is difficult. As the water heats in the process of
boiling, tiny bubbles appear on the bottom of the vessel in which it is
contained and rise to the surface. Then, gradually, the bubbles increase
in size until large ones form, rise rapidly, and break, thus producing
constant agitation of the water.

38. Boiling has various effects on foods. It toughens the albumin in
eggs, toughens the fiber and dissolves the connective tissues in meat,
softens the cellulose in cereals, vegetables, and fruits, and dissolves
other substances in many foods. A good point to bear in mind in
preparing foods by boiling is that slowly boiling water has the same
temperature as rapidly boiling water and is therefore able to do exactly
the same work. Keeping the gas burning full heat or running the fire
hard to keep the water boiling rapidly is therefore unnecessary;
besides, it wastes fuel without doing the work any faster and sometimes
not so well. However, there are several factors that influence the
rapidity with which water may be brought to the boiling point; namely,
the kind of utensil used, the amount of surface exposed, and the
quantity of heat applied. A cover placed on a saucepan or a kettle in
which food is to be boiled retains the heat, and thus causes the
temperature to rise more quickly; besides, a cover so used prevents a
loss of water by condensing the steam as it rises against the cover. As