A. The white crust is the salt of the water left on the clothes by evaporation.
Q. Why does this white crust always disappear in wet weather?
A. In wet weather the moisture of the air dissolves the salt; and, therefore, it no longer remains visible.
Q. Why should not persons, who take violent exercise, wear very thick clothing?
A. When the heat of the body is increased by exercise, perspiration reduces the heat (by evaporation) to a healthy standard: as thick clothing prevents this evaporation, and confines the heat and perspiration to the body, it is injurious to health.
CHAPTER XIII.
COMMUNICATION OF HEAT.
1.—CONDUCTION.
Q. How is heat communicated from one body to another?
A. 1. By Conduction. 2. By Absorption. 3. By Reflection. 4. By Radiation: and 5. By Convection.