THE OCEAN OF AIR 



4. Read something from the books listed as "Refer- 

 ences for Further Study" (p. 6). 



5. Close your book and think over the things you 

 have observed and read in such a way as to organize 

 the topic in your mind. 



6. Check your knowledge by means of the section, 

 "What You Should Aim to Acquire from This Study" 

 (p. 7). You will then be ready for the mastery test. 



7. In the study of this 

 topic you may meet some 

 words for the first time. 

 Study them carefully un- 

 til they become a part of 

 your vocabulary. 

 altitude height above a 



given level. 



aneroid without liquid. 

 barometer a device for 



measuring air pressure. 



diaphragm a thin disk or 

 membrane. 



pressure a push or pull on 

 a unit area such as one 

 square inch or one square 

 FIG. 1 centimeter. 



EXPERIMENTS OR DEMONSTRATIONS WHICH WILL 

 HELP ANSWER THE PROBLEM QUESTIONS 



Experiment 1. Does air have weight? 



Secure a simple balance as shown in Figure 1 and counter- 

 balance an empty football or basketball bladder with weights 

 or sand. Pump air into the bladder and close the neck with 

 a rubber band or piece of string and observe what happens. In 

 your notebook 1 enter notes on the experiment and complete 

 the following statements. When air was pumped into the 

 Dladder and it was closed, the bladder side of the balance 



weighed (more, less, the same) This would indicate 



that air . 



Experiment 2. Does air exert pressure? 



Secure a can like the one shown in Figure 2 or one 

 similar to it, which can be tightly closed. Put about an inch 

 of water into the can and 

 heat it until steam comes 

 from the opening. Close the 

 opening quickly and tightly 

 and cease to apply heat. Let 

 the can cool for a few mo- 

 ments and see what happens. 

 Try to crumple a similar can 



in your hands. In your note- 

 book 2 write a clear statement 

 of what was done. Complete 

 the following statements. 



(Air, Steam) filled the can when it was stoppered. 



When the flame was removed, the began to , caus- 



FIG. 2 



1 See p. 2 of workbook to accompany this text. 

 '' See p. 2 of workbook to accompany this text. 



ing less pressure of the can. The greater of the 



air on the of the can then caused it to . 



Under the heading, "Inferences and Conclusions," com- 

 plete the .following statement. The evidence above would 

 seem to indicate that air . 



Have your notes checked. 



If possible, try other experiments to test your conclu- 

 sion. 



Suggestion: Fill a glass very full of water and press a 

 piece of cardboard over the open end. Invert the glass and 

 remove your hand from the cardboard. Record the results 

 in your notebook. Did the experiment support or disprove 

 your conclusion? 



Experiment 3. How can air pressure be measured ? 



Close one end of a piece of 

 glass tube about thirty-two inches 

 in length by rotating it in a gas 

 or alcohol flame. Attach a funnel 

 to the open end of this tube by a 

 short length of tight-fitting rub- 

 ber tubing. Carefully pour mer-. 

 cury into the funnel until the tube/ 

 is full. Partly fill a shallow disn 

 with mercury. Placing your fingfcr 

 over the open end of the tube, 

 turn the closed" end up. Be caYe- 

 ful not to remove your finger 

 from the tube until the open end 

 is under the surface of the rher- 

 cury in the dish. Support Ithe 

 barometer tube by means of a ring 

 stand as shown in the diagram. 

 Measure the height of the mer- 

 cury column above the level of the 

 mercury in the dish. Take read- 

 ings for several days. In your notebook 3 record what was 

 done. Make a table of the measurements of the mercury 

 column for several successive days. 



Under the heading, "Observations and Inferences," com- 

 plete the following statements. holds the mercury up 



the tube. The mercury column fell when the tube was in- 

 verted because The mercury did not fall all the way 



down the tube because The space above the mercury 



column is probably a The height of the mercury 



column might be measured in what units? The height of 



the mercury column is an indication of the of the 



atmosphere. The mercury column balances a column of air 



as deep as the The mercury column is shorter than 



the air column because it m'ore, volume for volume. 



The data from the table seem to indicate that air pressure 



from day to day. When the pressure increases, the 



mercury column When the mercury column falls, the 



pressure . 



Experiment 4. How does the aneroid barometer meas- 

 ure pressure? 



Secure an aneroid barometer similar to the one in Fig- 

 ure 4. Study the working parts carefully, noting particu- 

 lar the round shiny box in the center. Observe the way 

 in which the dial is marked and any words or letters which 

 appear. Compare the reading of the aneroid with the height 

 of your mercury barometer. 



3 See accompanying workbook, p. 3. 



FIU. 3. MEASURING THK 

 HEIGHT OF A BAROMETRIC 

 COLUMN 



