2081. Yes; when the teapot is set on the hob to "draw," the black earth is the best, because it absorbs heat; but when the teapot is not set on the hob the bright metal is the best, because it radiates heat very slowly, and therefore keeps the water hot.
2082. Why does a saucepan which has been used boil in a shorter time than a new one?
2083. Because the bottom and back are covered with soot, and the black soot rapidly absorbs the heat of the glowing coals.
2084. Why should the front and lid of a saucepan be clean and bright?
2085. As they do not come in contact with the fire, they cannot absorb heat, and (being bright) they will not suffer the heat to escape by radiation.
2086. Why should not the bottom and back of a kettle be cleaned and polished?