A. Prepare Stuffed Potatoes.
Wash a potato, scrubbing it well with a vegetable brush. Bake in a hot oven until soft. Cut a piece off the top and remove the contents with a fork, taking care not to break the skin. Mash the contents with a little butter, salt and pepper, and moisten with hot milk. Replace in the skin and reheat.
B. Class Experiments. Drafts.
1. What is the effect of a draft in a stove? Try the following experiments to find out: a. Put a lamp chimney over a lighted candle, but hold it so high that it will not touch whatever the candle is standing on. Take small pieces of some light material (threads of cotton wool will do) and hold them first above the chimney, then underneath it. Is the draft passing through the chimney and in what direction, up or down?
b. Place a lighted candle in a saucer of water, and put the lamp chimney over it so that it, too, rests in the water. Why does the candle go out ?
c. Fit a piece of pasteboard lengthwise into the lamp chimney. Relight the candle and replace the chimney, but set it so that the candle flame is on one side of the pasteboard partition. Why does the candle behave differently ? Test the draft.
d. Take an empty pasteboard shoe box. Cut two holes in the cover, one at each end.
Each hole is to be a little smaller than the bottom of a lamp chimney. With a drop of melted wax, stick a lighted candle to the bottom of the box so that the flame will be under one of the holes when the cover is put on. Cover, and put a lamp chimney over each hole. Test the draft by holding threads of the light material over each chimney.
2. Examine a wood or coal stove, or range. Is there a place for the air to come in as well as a place for the products of combustion to pass out?
Can the size of these openings be regulated ?
Since air or oxygen is necessary for combustion, there must be a constant supply of air, as in a draft, for a fire to continue burning. The fire-box, then, in a stove could not be air-tight. The air coming in the door below the fire ordinarily passes out directly through the stove-pipe. The check draft in the stove-pipe may, at will, be left wide open, or turned so that it nearly closes the pipe. Besides these two means of controlling the supply of air, there is a third way. The upper door into the fire-box or a lid on top of the stove may be left open. This allows the cold air to blow across the top of the fire and cool it so that it will burn much more slowly.
A fire merely built beside an oven would heat it unequally, so arrangements are made to allow the hot gases from the fire to pass entirely around the oven when it is desired to heat it. This is accomplished by shifting the oven damper. This closes the direct opening into the stovepipe and so forces the gases to pass around the oven before escaping.
The arrows show circulation of air through A, directly to smoke-pipe, and through B, indirectly around oven.
Notice that there is a handle which may be fitted on a bar from the grate. By turning the handle the grate may be rocked back and forth to shake down the ashes. The fire-box itself is lined with fire-proof material to protect the iron as much as possible from gradually burning out. The top of the stove cannot be so protected, so care must be taken to keep the fire low down in the fire-box. This means a saving of coal, too, and generally gives as efficient a fire.
Anything spilled on a stove should be wiped off immediately with soft paper or cotton waste. If necessary, soap and water or sapolio can be used later, or, when cold, the top may be cleaned by rubbing with a few drops of kerosene. In order to protect the iron from rusting, it is necessary to keep it well covered. Blacking is usually used for this purpose. The blacking is rubbed on while the stove is cold and polished when it is warm. A stove that is to be out of use for some time is still better protected by covering it with a thin coating of oil or grease.
It is interesting to consider why heating a portion of the air causes a draft. This is because the heated air expands so that the amount present in any given space is less than it was before. It is therefore lighter. But this light air is surrounded by cold air, which is heavier and so is pulled down harder by the attraction of gravitation which pulls everything toward the earth. The cold air, being pulled harder, naturally displaces the warm air and so pushes it up. It is often said that hot air rises, but this is not strictly true, because it would not rise at all if it were not for the colder, heavier air around it.
In the ventilation of rooms advantage is taken of the fact that the circulation of air is caused by differences in temperature. Hoods are often installed over stoves to carry off the odors of cooking. These work in the manner indicated above, the hot air over the stove being pushed up into the exit pipe by the colder air around. The hood itself acts merely by confining the warm air and preventing it from scattering.
U. S. Dept. of Commerce. Bureau of Standards, Circular No. 55, sections on Amount of Heat used in Cooking and Some Other Household Operations, Regulation of Stoves, Ranges, and Other Heating Appliances, and on Oven Thermometers.
1. Why does a match go out if it is blown or shaken too hard?
2. Why does a fire burn more brightly if it is blown with a bellows? Why does it not go out?
3. Explain why, in building a coal fire, paper and wood are also used. Why is the paper twisted and crumpled and the wood laid criss-cross ?
4. How is an oven heated, and how is the temperature of an oven controlled?
5. What difficulty occurs if the ash pan is allowed to get too full?
6. Why should ashes and soot be frequently removed from the flues back of and under the oven?
7. Why is a fire lighted at the bottom and not at the top?
8. How would you arrange to keep a fire over night? Give the reason for each act.
9. What is the danger in allowing coal gas to escape?