Other Facts about Heat
If a stopper is left off a cologne bottle, the contents of the bottle will slowly evaporate; if a dish of water is placed out of doors on a hot day, evaporation occurs very rapidly. The liquids which have disappeared from the bottle and the dish have passed into the surrounding air in the form of vapor. We know that water could not pass into vapor without the addition of heat; now the heat necessary for the evaporation of the cologne and water was taken from the air, leaving it slightly cooler. If wet hands are not dried with a towel, but are left to dry by evaporation, heat is taken from the hand in the process, leaving a sensation of coolness. Damp clothing should never be worn, because the moisture in it tends to evaporate at the expense of the bodily heat, and this undue loss of heat from the body produces chills. After a bath the body should be well rubbed, otherwise evaporation occurs at the expense of heat which the body cannot ordinarily afford to lose.
Evaporation is a slow process occurring at all times; it is hastened during the summer, because of the large amount of heat present in the atmosphere. Many large cities make use of the cooling effect of evaporation to lower the temperature of the air in summer; streets are sprinkled not only to lay the dust, but in order that the surrounding air may be cooled by the evaporation of the water.
Some thrifty housewives economize by utilizing the cooling effects of evaporation. Butter, cheese, and other foods sensitive to heat are placed in porous vessels wrapped in wet cloths. Rapid evaporation of the water from the wet cloths keeps the contents of the jars cool, and that without expense other than the muscular energy needed for wetting the cloths frequently.