55. Exercises.

- 1. Watch a person who breathes through his

mouth; does such breathing affect his appearance?

2. How do you ventilate your sleeping-room? How should it be ventilated?

3. Tell how your schoolroom is ventilated.

4. What should be done with a child that breathes through its mouth?

5. How should people having tuberculosis be treated?

6. What is the real value of breathing exercises?

7. Is there any evidence of a greater amount of moisture in the air of your house on a wash day than on other days? Tell what happens and why.

CHAPTER VIII

HEATING THE AIR OF THE HOUSE

56. How Do We Heat the House?

mean when we say that we heat our houses? Is it not that we heat the air of our houses and that it is through the heated air that we get heat to the objects of the house? When we say that we "keep in the heat" and "keep out the cold," we mean that we keep in, or keep out, as the case may be, the heated or cold air.

57. Fireplaces. -To heat their dwellings men have used open fires, fireplaces, stoves, hot-air furnaces, and hot-water, steam, and electric heaters. The Indian built a fire on the floor of his wigwam and let the smoke escape through a hole in the top. The Eskimo uses blubber (fat obtained from the whale) as the fuel to heat his house, or igloo. You may imagine the smoke and odors of these barbarous fires. Civilized man has improved greatly on these methods.

Nowadays we are likely to think of the fireplace as merely an ornament, but it is really very useful, no matter how the house is heated. It helps greatly in ventilating a house (cf. §§ 49 and 60), for it carries out the air near the floor and so makes room for fresh air.

In the early days of this country all heating, both for cooking and baking and for heating the house, was done by the fireplace (Fig. 35).

The andirons kept the fuel up from the hearth, so that air currents would be drawn through the fire. A crane (a swinging frame) could be swung out over the fire. From it, by means of chains, the kettles were hung. Kettles were also mounted on three legs, so that hot coals could be put under them. The backlog was a large log placed at the back of the fireplace. The forestick was in front, on the andirons; between the backlog and the forestick the smaller fuel of the

FIG. 35. — Fireplaces are put into modern houses waste gases. The both for beauty and for use.

whole

opening serves for the entrance of fresh air.

fireplace

In a stove the

fire is surrounded closely on all sides. There are dampers to control the entrance of air and a pipe to carry off the waste gases. In place of the andirons, there is a grate to hold the fuel up, so that air may pass through it. In a cookstove both the top of the stove and the oven must be heated, hence the stove has a "back damper" which does not allow the hot, waste gases to escape at once,

but compels them first to travel around the oven and thus to heat the oven. Examine a stove and make out the course taken by the air that passes through it.

59. How Does a Fire Warm Us? Put a flatiron on a hot stove; what happens? The iron becomes hot because the heat of the stove is passed over, or conducted, directly to the iron. To touch the handle of the flatiron with your hand would make a painful burn. To prevent this you use a nonconductor of heat, such as a pad of cloth or asbestos, or a wooden handle. If you put your hand into warm water, the heat of the water is conducted to your hand. When you put your hand into cold water, your hand gives heat to the water. The colder body or object is warmed by conduction. The air that touches a stove is also warmed by conduction.

But suppose you sit before the fire of a fireplace. The currents are all rushing toward the fire, so the air is not bringing heat to you. You are not touching the fireplace. Therefore you are not getting heat by conduction. How does the heat get to you? It would come to you whether you were above the fire, or below it, or on one side, just as the light of a lamp does. We say that the heat of the fire, like the light of a lamp, is radiated to you. Radiated is a word coming from radius, meaning the spoke of a wheel. The heat of the sun, as well as its light, comes to us by radiation through space. There are, then, two ways in which heat can come to us from a fire: (1) by conduction; (2) by radiation, in the form of "heat rays."

60. Hot-air Furnace. Sometimes we speak of the way in which air rises when heated and falls when cooled as a third way of distributing heat: convection (cf. § 49). You can see that this is really not a new way at all, because in order that there may be warm convection currents

FIG. 36.

pot

Coal
Door

Ash pit

Lower
Draft

ހ

A hot-air furnace is a fire

in the air, the air must be heated by touching a hot body (conduction) or by means of heat rays (radiation).

The hot-air furnace makes use of the principle of convection currents. The air is heated in a tight "drum" which entirely surrounds the firepot of the furnace. When a fire is burning in the firepot, air currents are formed in the drum. As a result, warm

pot surrounded by a "drum" in which air rushes up through the

air currents are formed.

register, rises into the room, is cooled, falls again, and goes into the cold-air register, to be taken back to the drum to be reheated. You can understand the hot-air furnace better if you will study Fig. 36. From time to time fresh, outside air comes through the "cold-air intake" and after being heated is distributed to the house.

Do you think there are convection currents in a refrigerator? In order to cool the whole refrigerator,