DEVICES USING AIR PRESSURE 



WHAT YOU SHOULD AIM TO ACQUIRE FROM 

 THIS STUDY 



1. A knowledge of how air is weighed. 



2. An understanding of why air exerts pressure 

 and how its pressure is measured. 



3. An understanding of how the mercury barometer 

 and the aneroid barometer are constructed and how 

 they work. 



4. Skill in reading each type of barometer. 



5. An understanding of the uses of barometers. 



OF MASTERY OF THE TOPIC 



This exercise is not a test to be graded but a device to 

 help you discover the things which have not been done 

 thoroughly and which, therefore, need more study. It should 

 be done without any assistance. 



Under the heading "Tests of Mastery" in your note- 

 book, complete the following statements, answer the ques- 

 tions, and comply with the instructions. 



1. Air exerts because of its 



2. Standard air pressure is measured at 



3. What is the unit in which air pressure is measured? 



4. The atmosphere is thought to be about in depth. 



5. A column of mercury high at sea level balances a 



column of air as high as the . is deep. 



6. In a mercury barometer the height of the column of 

 mercury is measured from the level in the to the level 



is a (spring, box) 

 been removed. 



from which (air, water) 



has 



7. The basic operating part of the aneroid barometer 



8. What instrument does an aviator use to tell his alti- 

 tude? 



9. What is the normal atmospheric pressure in pounds 

 per square inch? 



10. Who first used mercury as a barometric liquid? 



11. Mercury is how many times heavier than water? 



12. What is a recording barometer called? 



13. Make a diagram showing how the vacuum box of 

 an aneroid barometer is constructed. 



14. Man has explored the atmosphere to a height of 



miles in the airplane and to a height of miles 



with the sounding balloon. 



15. A water column (20, 33) feet high presses as 



much as a mercury column (20, 30) inches high. 



16. When reading a mercury barometer the eye should 

 be on a level with . 



17. If a single hole is punched in a can of condensed 

 milk or other liquid, the contents do not run out readily. 

 How can the liquid be made to run out more rapidly ? Why ? 



18. Many liquids will nat run from small-necked bot- 

 tles except as bubbles enter. Explain. 



19. In the cap of the gasoline tank of an automobile 

 is a very small hole. Can you infer the use of this? 



20. Two army officers recently reached a height of about 

 73,000 feet in a balloon. At this altitude their barometer 

 registered 29 millimeters (a little more than one inch) of 

 mercury as compared with 760 mm. (30 inches) at sea level. 

 What inference would you draw from these data? 



21. In making nights into the stratosphere, the huge bal- 

 loons are only partly filled with gas. Can you infer the 

 reason for this? Predict the effect at a high altitude if 

 the balloon were completely inflated at the earth. 



TOPIC 2. SOME DEVICES WHICH USE THE PRESSURE OF AIR 



L 



SUGGESTED PROBLEMS AND QUESTIONS 



1. How long have pumps been known? 



2. What are pumps used for in modern life? 



3. How do lift and force pumps work? 



4. How does an automobile or bicycle pump 

 work? 



5. What is a siphon and how does it work? 



6. What are some of the uses of the vacuum? 



7. How do we make use of air pressure in breath- 

 ing? 



SUGGESTIONS AND HELPS FOR STUDY 



Refer to "Suggestions and Helps for Study," p. 1. 



In the study of this topic certain words which you 

 should know will be met for the first time. Study them 

 carefully and refer to them frequently that they may 

 become a part of your vocabulary. 

 piston a closely fitting plug in a cylindrical chamber 



so constructed that it will move back and forth. 

 siphon a tube through which liquids are moved from 



high levels to low levels by means of air pressure. 



suction the act of drawing a substance in one direction 

 by means of unequal pressure. If pressure from one 

 side is reduced, the object is moved in that direction 

 by the force on the other side. 



vacuum a space which contains no air or other sub- 

 stance. 



valve a device used to close and open small passages. 





EXPERIMENTS OR DEMONSTRATIONS WHICH WILL 

 . HELP ANSWER THE PROBLEM QUESTIONS 



Experiment 5. How is a lift pump constructed and 

 how does it work? 



Secure a commercial kitchen lift pump and unbolt the 

 bottom section with a wrench. The top may be removed 

 by loosening the set screw which holds it. Examine the 

 valve at the bottom and the valve in the piston or plunger. 

 Reassemble the pump and study its operation by pumping 

 water with it. If a glass model lift pump is available, study 

 the action of the valves. A glass model lift pump may be 

 constructed as shown in the diagram (Fig. 14). The cylin- 

 der is a straight-sided lamp chimney. The piston is a two- 

 hole rubber stopper ; attached to it by a brass thumb tack is 

 a valve flap made of leather to cover one hole. The base 

 is a one-hole rubber stopper with a leather flap for the foot 

 valve. The handle may be of wood, or a brass rod may be 

 inserted in the other hole of the piston stopper. 



