RELATION OF AIR TO THE CANDLE FLAME (VI−1)

Problem. It has already been suggested that air is not composed of a single substance. We have found that water vapor is often present in a considerable amount. In the Bunsen burner, in the gas-stove burner, and in the gas lamp air is always mixed with the gas. Flames from such mixtures are very hot and have the advantage of depositing no soot. In order to obtain more information about the other gases in the air and the

part they play in burning, in breathing, and in plant growth, we may begin with the simple candle flame.

What to use. Large tallow or paraffin candle, matches, Bunsen burner, glass tubing four inches long (jet tube), test-tube holder or wire, wide

mouth bottle, and lime

water solution.

FIG. 13

LIME WATER

What to do. 1. Light the candle (Fig. 13). Find three layers, or zones, in the flame. The inner zone is dark, the middle zone is bright, and the outer zone is a pale blue layer over the middle zone. Make a full-size drawing of the three zones and color them. Label the parts.

2. Hold a piece of white paper stretched horizontally between the hands, and quickly thrust it into the flame in such a position that the center of the paper is just above the wick. When the paper begins to char, remove it quickly. Examine for the heating effect of the different zones. Make a drawing of the charred paper.

3. Hold a match or small splinter of wood across the flame ; examine as in 2.

4. Hold the jet tube (use a test-tube holder) with the large end in the center of the flame. Bring a match to the tip of the tube. Allow the tube to cool; note the inner part of the tube.

5. Hold a cool, dry, wide-mouth bottle over the candle flame so that the mouth of the bottle is about two inches from the flame. Remove and examine after about one minute.

6. Repeat 5, then add about ten cubic centimeters of lime water to the bottle, cover with the hand, and shake. (When limewater and carbon dioxide are mixed, a substance forms which clouds the water.)

Questions. Describe the appearance of the three zones of the flame. Which one is the hottest? which the coolest? What do the results with the paper and the match indicate? What do the results in 4 show? What do you observe in 5? What is the source of the substance found in the bottle in 5? Drops of water often collect on the cool kettle when a gas stove is lighted. Explain. What results do you get in 6? Explain.

Suggestions for report. After class discussion write correct answers for the questions given above and use this statement and the drawings as a report of the experiment.

Reference work. Read sections 65 to 75.

Optional problems. Perform this experiment with the Bunsen flame. Note carefully the results and compare with the results of the experiment with the candle flame. Explore the Bunsen flame with a match head to see if the match may be held in the flame without burning it. Expose a wide dish of limewater to air for twenty-four hours. Note and explain the results. Study the gas stove and compare it with the Bunsen burner.

NATURE OF THE WATER PRODUCED IN

THE CANDLE FLAME (VI−2)

Problem. The results of previous experiments indicate that water is one product of the candle flame and the gas flame. What is the source of this water and what is the process by means of which it is produced? In 1781 water was shown to be a compound of two gases. It is possible to obtain interesting information by decomposing water. This can be done by send

ing an electric current through water (properly treated) and collecting the products.

What to use. Ring stand, one ring, milk bottle (see appendix, p. 181, for method of removing the bottom), rubber stopper to fit, two carbon rods, connecting wires, three or four dry cells, switch, concentrated sulfuric acid, two eight-inch test tubes, and matches. The apparatus illustrated on

page 67 of the text can be used.

What to do. 1. Assemble the apparatus as shown in figure 14.

FIG. 14

Partially fill the bottle with water and measure it. Then pour into the bottle of water, slowly and with constant stirring, one part of concentrated sulfuric acid for each twenty parts of water. Caution! Do not pour water into the acid.

2. Fill two test tubes with the water and invert them, as shown in the figure.

3. Let the current flow through the solution until one tube is half full of gas. Note the quantity that is in the other tube. For exact quantities use apparatus shown on page 67 of the text.