CHAPTER VII.
HOW HEAT IN THE AIR BECOMES LATENT, AND HOW IT GETS FREE AGAIN.
In the preceding chapter it was shown how warm air produces evaporation, and how cold air causes rain and snow. In this chapter we desire to demonstrate how the reverse may take place, viz., the engendering of cold and heat by evaporation and rain.
Although what we wish to prove in the following is firmly established, yet it is not easy to make it understood. For this reason many educated men, who have read much about "free and latent heat," have mistaken ideas about it.
In order that what we shall explain may be in the reach of every one, we must again choose our examples from life itself, and request our readers to come to our aid with their thoughts.
Every one knows how water is boiled. It is placed over the fire, the heat of which communicates itself to the water and heats it more and more. Now, where does the heat of the fire go? It is taken up by the water; thus to speak, the water absorbs the heat. This explains why a cooking-stove on which a dinner is cooked, does not get near as warm as it would, if the same quantity of fuel had been used without any cooking on the stove. For a portion of the heat being absorbed by the meat, it cannot heat the stove; hence the stove fails to receive the amount of heat that is used in cooking the meat.
What will be the effect of taking boiling water from the stove and placing it in the room somewhere? Where will the heat of the water go then?
We all know that in this case the water cools down by degrees. The water gives out its heat. Now, it is evident that while on the fire, the water had absorbed heat; and that it gave out that heat on being put in a colder place.
But what will become of the water if it is allowed to continue to absorb heat? What becomes of a pot of water, if, on beginning to boil, it is not taken off the fire? Does such water continue to absorb heat?