Note

Student explain the steps in fire building by which hard coal may be raised to its kindling point.

Flash Point

The temperature to which a fat or oil must be raised before an inflammable vapor is given off is called the flash point. This is a valuable indication of the safety of an oil.

Fuels

A fuel is a combustible substance usually composed of carbon and hydrogen.

Note

Student prepare a list of fuels -

Note

Students inspect specimens of hard and soft woods; charcoal; peat; bituminous, anthracite, and cannel coal; various fuel oils; alcohols.

Students write paper on the "Story of Coal."

Students procure the current market price of the various fuels listed above. From the cost of a basket of coal or "bundle of wood," estimate the price paid for a ton of coal and a cord of wood when purchased in small quantities.

Heat

Heat is molecular motion. Sources of heat:

1. Mechanical energy.

Produced by friction or by collision.

2. Chemical energy.

Produced by combustion or by chemical union of different compounds or elements.

3. Electrical energy.

As produced by an electric toaster, etc., or by the sun's rays. Heat is transferred from one body to another or to different parts of the same body by conduction, convection, and radiation.

Conduction:

Experiment 8

Place rods of wood, metal, and glass on an asbestos mat over a gas burner with the ends of the rods extending beyond the mat. The metal rod will soon become hot, while the other two will not be appreciably heated. Metals are good conductors of heat and cold, glass and wood are poor conductors. Air is a very poor conductor.

The conduction of heat consists of the transfer of motion from molecule to molecule.

Note

Students make a list of good conductors; of poor conductors.

Why are wooden handles placed upon teakettles, flat-irons, etc.? Why is the handle of a kettle sometimes made in the form of a spiral ? Why is the outer portion of an ice cream freezer made of wood? Why is the inner can made of metal? What is the principle upon which a fireless cooker is constructed? a thermos bottle? How should the oven of a stove be constructed?

Convection:

Experiment 9

Partly fill a glass beaker with water, add one half teaspoon of sawdust, and heat slowly. A movement will be seen in the sawdust, indicating that the heat sets up currents in the water which have an upward direction immediately over the flame. The water nearest the flame becomes heated and expands; this makes it lighter and it rises, while the cold water of the top takes its place, thus causing the currents noted. This method of heat transference, which takes place in liquids and in gases, is called convection. There are convection currents in the atmosphere, caused by the unequal heating of the earth by the sun. The air over a heated portion of the earth rises, and the cool air rushes in to take its place.