and assemble the burner with care. To light the Bunsen burner, turn on the gas, then bring a burning match to the top of the burner. Turn the gas cock until the flame is about four inches high. Adjust the air regulator until a blue flame with a slight greenish cone is obtained. Always use the blue flame instead of the yellow flame unless otherwise directed.

4. Warm the test tube slowly and uniformly with the Bunsen flame, turning the tube slowly as you heat it.

Questions. What occurs when the hands are placed on the test tube? Why? What occurs when the hands are removed? Why? Why is one part of the burner called a mixing chamber? Explain the purpose of the air regulator. What makes the flame yellow when the air regulator is closed? What is the green cone in the flame? Is it hot? How do the results in 2 differ from 4? Why?

1

Suggestions for report. Make a cross-section diagram of the apparatus used. Write a complete account of the experiment according to the suggestions given on page 1.1

Reference work. Read sections 12, 14, and 15. Automobile tires sometimes burst while standing in the sun. Explain. How do you account for the upward currents of air near a stove, lamp, or radiator? Why does smoke go up a chimney? How is a gas stove like a Bunsen burner?

Optional problems. Can you make an "air thermometer" with a test tube, a one-hole rubber stopper, a glass tube eighteen inches long, and a Bunsen burner? Can you make a Bunsen burner with a No. 1 cork and six inches of glass tube, a set of cork borers, and a Bunsen flame? Can you devise a new experiment to show that air expands when heated?

1 On page viii there is given an outline for a completely written report. It is not thought necessary to have all reports as fully written as there indicated, but some should be so written in order to develop the habit of complete description."

VENTILATION (I-7)

The problem. It is estimated that a man exhales six cubic feet of carbon dioxide per hour. A gas light may produce 3.75 cubic feet of this gas in the same time. As carbon dioxide is produced oxygen is consumed. In order to have an ample supply of oxygen some circulation of air must be obtained. These and additional facts make it necessary to ventilate the rooms of buildings. The usual method is to open one or more windows. Should these be open at the top or at the bottom, or both? If more than one window is opened should they be on

the same side of the room?

What to use. Box as shown in figure 7, candle, punk or touch paper (soak filter paper in a solution of potassium nitrate and dry).

What to do. 1. Arrange the apparatus as shown in

FIG. 7

figure 7. Close all the holes. Light the candle and place it in the box. Watch the flame carefully for several minutes.

2. With the candle lighted as before remove one of the stoppers. Try different arrangements of openings until you find the smallest number of openings with which you can secure a large flame.

3. Trace the course of the air into and out of the openings by holding a smoking object near the holes. Make a diagram showing the path of the currents.

4. Arrange the box to represent your room. Place the candle in the position occupied by your bed. Secure the best ventilation possible and then draw a diagram showing the air currents.

Questions. How does the candle flame resemble the Bunsen burner? Does the candle burn continually in the box? Why?

What is the course of the air currents? What arrangement did you have for 2? for 3? for 4? Summarize the chief facts shown by the experiment.

Suggestions for report. Correct answers to the questions above should be recorded in the notebook.

Reference work. Read sections 15 to 18. Make a diagram of your room at home, showing the heating and ventilating system (see Fig. 15 of the text). Show the points of likeness and difference between figures 15 and 18 of the text.

Optional problems. Can you determine the course of the air currents about a Bunsen burner? a lamp? a gas stove? an open door? an open window?