Q. Why is broth cooled by being left exposed to the air?
A. Hot broth throws off some heat by radiation; but it is mainly cooled down by convection.
Q. How is hot broth cooled down by convection?
A. The air resting on the hot broth (being heated) ascends; colder air succeeding absorbs more heat, and ascends also; and this process is repeated, till the broth is made cool.
Q. Why is hot tea and broth cooled faster, for being stirred about?
A. 1st—The agitation assists the liquor in bringing its hottest particles to the surface:
2ndly—The action of stirring agitates the air, and brings it quicker to the broth or tea: and
3rdly—As the hottest particles are more rapidly brought into contact with the air, therefore convection is more rapid.
Q. Why is hot tea, &c. cooled more rapidly by blowing it?