HOW DO WE BREATHE? 73 



I. Air: (1) fills " empty " glasses; (2) is dissolved in water of 

 falling raindrops ; (3) is a factor in winds ; (4) is present in most 

 soils ; (5) brings us light and heat from the sun. 



II. The air is useful because it supplies us with : (6) oxygen ; 

 (7) carbon; (8) hydrogen; (9) argon; (10) water for clouds. 



III. Exhaled breath contains some: (11) oxygen; (12) nitro- 

 gen; (13) carbon dioxide ; (14) water vapor ; (15) sulphur dioxide. 



IV. Oxygen from the air is used in : (16) rusting iron ; (17) tar- 

 nishing silver ; (18) fires; (19) electric lamps; (20) making a gas 

 flame. 



V. The following assists one in taking air into the lungs : 

 (21) muscular action in chest wall; (22) the larynx; (23) the 

 upward curving of the diaphragm ; (24) atmospheric pressure ; 

 (25) the movement of blood through the tissues of the lungs. 



VI. The pressure of the atmosphere : (26) depends upon the 

 fact that air has weight ; (27) can be measured with a thermometer ; 

 (28) will hold up a column of mercury nearly 34 feet high at sea 

 level ; (29) can be removed from a surface ; (30) is greater at the 

 top of a mountain than at sea level. 



VII. A vacuum: (31) has only air in it; (32) does not contain 

 any matter ; (33) is useful in making the atmosphere do work ; 

 (34) is used to make balloons rise; (35) can be made by blowing 

 all the air out of a bottle. 



VIII. Canned molasses and evaporated milk are easily poured 

 out : (36) from a hole in the center of the top of the can ; (37) when 

 two holes at opposite edges of the top are made ; (38) from a single 

 small hole near one edge of top ; (39) from two small holes close 

 together ; (40) when the entire top of can is cut out. 



IX. Expiration in the process of breathing is : (41) to stop 

 breathing; (42) to die; (43) to exhale air; (44) to inhale air; 

 (45) to force all air from the lungs. 



X. A vacuum can be made in a vessel by (46) condensing 

 steam in it ; (47) filling with water to get rid of air and then pouring 

 the water out ; (48) pumping air into it ; (49) blowing through 

 a tube into a bottle ; (50) by squeezing an atomizer bulb and then 

 releasing it. 



THOUGHT QUESTIONS 



1. Oxygen, carbon dioxide, water vapor, nitrogen, and dust 

 are constantly being taken from the air and they are constantly 

 being returned to the air. Make a diagram to show the " cycles " 

 of these substances ; that is, show all the ways by which they are 

 removed from the air, 



