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THE ACTION OF COMPRESSED AIR (1-2)
The problem. The extensive use of compressed air is one of the interesting developments of modern civilization. The automobile tire, football, bicycle tire, passenger train, street car, interurban car, subway car, freight car, rock drill, dentist's drill, thermostat, doorstop, and many other devices utilize compressed air in some way. What qualities of compressed air make it so useful in these appliances ?
What to use. Wide-mouth bottle with two-hole rubber stopper to fit, glass plug for one hole, jet tube six inches long, glass tube six inches long, two inches of rubber tubing, clamp, and water.
What to do. 1. Assemble the apparatus as shown in figure 2. Prepare the jet tube as suggested in the appendix.
2. Open the clamp and blow into the bottle as much air as possible. While blowing, close the tube with the clamp, then remove the tube from the mouth.
3. Tip the mouth of the bottle away from you and open the clamp. Repeat 2 and 3 until all of the essential facts have been observed.
Fig. 2 4. Answer the questions in the following paragraph.
Questions. Why do bubbles appear as you blow into the bottle? Why is the tube closed before it is removed from the mouth ? What drives the water out of the bottle ? Why is all of the water not driven out? Why does water remain in the upper part of the tube ? How is it possible to get so much air into the bottle ?
Suggestions for report. After a class discussion of the answers, they should be revised and recorded in correct form.
Reference work. Explain how one important fact shown by the experiment is used in any compressed-air appliance. Make a list
of all the uses of compressed air that you have seen. By means of a diagram similar to figure 3 of the text, explain the action of a bicycle pump.
Optional problems. The chemist makes a wash bottle for forcing distilled water against glassware, etc. Can you devise one with this apparatus, using it and an extra piece of glass tubing ? Make a study of the doorstop or other air appliance and explain its action. .
SOME USES OF THE VACUUM (1-3)
The problem. No less interesting than the employment of compressed air are the uses made of a chamber from which a part or all of the air has been removed, commonly called a vacuum. The vacuum is utilized in incandescent electric lamps, cleaners for the household and street, mercury barometers, thermos bottles, thermometers, X-ray tubes, and wireless telegraph and telephone instruments.
What to use. Two wide-mouth bottles, pinchcock, two inches of rubber tubing, two-hole rubber stopper to fit the bottle, glass plug for one hole, jet tube, glass tube, and water. A ring stand and burette clamp can be used if available.
What to do. 1. Assemble the apparatus as shown in figure 3.
2. Suck out as much air as possible from the upper bottle, which
Fig. 3 is empty at the beginning of the experiment; close the pinchcock, quickly place the glass tube under water, and open the pinchcock. Repeat until you have removed from the upper bottle as much of the air as you can.
3. Answer the questions in the following paragraph.
Questions. Why does the water move when the pinchcock is released ? Will the apparatus operate without the jet tube? How much water enters the bottle? Why? How much air was removed ?