AIR AND LIVING THINGS 



25 



dioxide as a result of the slow burning which has taken 

 place. Fish have gills which enable them to secure 

 their oxygen from the air that is dissolved in water. 

 Trees and other plants obtain oxygen through leaves 

 and stems which have openings into the interior of 

 the plants. 



FIG. 46. A BALANCED AQUARIUM 



Oxygen for things which live in water is also ob- 

 tained from green plants that live in the water. As 

 these plants make food for themselves, oxygen is a 

 waste product and is breathed out through the same 

 openings which take in air dissolved in water. This is 

 the reason that green plants are important in an aqua- 

 rium. 



What is the importance of fresh air and how is it 

 best obtained in our buildings? Air may be easily 

 made unfit for breathing by the presence of dust par- 

 ticles, by tiny plants called bacteria, some of which 

 cause disease, and by gases which are given out from 

 the chimneys of some manufacturing plants and from 

 automobile engines running in closed buildings. 



While the removal of some of these impurities 

 from the air that we breathe is beyond our control, 

 one may do a great deal toward freeing his city from 

 smoke; this is one of the greatest problems of some 

 of our modern cities. In some .places laws preventing 

 any industry, apartment house, or other large build- 

 ing from throwing out dense smoke are carefully en- 

 forced. If your city has a smoke law, secure informa- 

 tion about it and do what you can to cooperate in its 

 enforcement. 



The coming of the automobile has brought a prob- 

 lem of impure air which seems to be one of the most 

 important of the present and future. You have already 

 learned that when anything containing carbon burns, 

 one of the products formed is carbon dioxide. This is 

 true, however, only when the burning takes place 

 where there is a plentiful supply of oxygen. Carbon 

 dioxide is harmless and may be breathed without fear. 

 If, on the other hand, a substance containing carbon 

 is burned where there is only a limited supply of oxy- 



gen, another oxide called carbon monoxide is formed. 



carbon + oxygen (limited) = carbon monoxide 

 Carbon monoxide is very poisonous even when 

 breathed in small quantities. In the cylinder of an 

 automobile where the gasoline, which contains carbon, 

 is exploded, the air supply is limited and, therefore, 

 some of the gas which is thrown out by the exhaust 

 of the car is .carbon monoxide. When this is allowed 

 to accumulate ^a&Jn a closed garage, it soon makes 

 the air unfit to breathy and will overcome and cause 

 the death of any living thing breathing it. Never start 

 or leave an automobile engine running in a closed 

 garage. To do so may cost yo\ your life. 



So much of our lives is spent indoors that we should 

 be very careful to insure in our working and sleeping 

 places an ample supply of fresh air free from draft. 

 Estimates vary regarding the amount of pure air 

 needed by each person, but there should be provided 

 at least 1600 cubic feet per hour per person. Everyone 

 becomes uncomfortable in ja closed room, not so much 

 from a lack of oxygen as from the increase in the water 



vapor present in the air. P 



to ventilate rooms that the 



removed while fresh pure a 



Air which has been brea 



ovision should be made so 

 breathed air can be readily 

 r is constantly supplied, 

 hed is warmer and lighter, 



volume for volume, than ifresh air, and so will be 

 pushed to the top of the rbom by the cool, heavier 

 fresh air. If a window is open at both the top and bot- 

 tom, cool fresh air can come in at the bottom and push 

 the lighter warm air out at the top. If possible, a 

 window in one part of the room should be open at the 

 bottom and one in another part of the room at the top, 

 thus providing for a circulating of the fresh air. 

 Since there is danger from draft, it is wise to place 



FIG. 47. PROPER VENTILATION 



at the lower opening of the window a board or screen 

 which slants inward. This will give the incoming air 

 an upward motion and will prevent it from blowing 

 on a person near the window. 



Air conditioning is important in modern homes and 

 public buildings. During the past few years many 



