24 



THE OCEAN OF AIR 



come to be important in the past few years. Helium, 

 because it is very light and will not explode, is used 

 for filling dirigible balloons. It is, however, obtained 

 from natural gas wells in Texas rather than from the 

 atmosphere. Neon is now used a great deal in the 

 making of electric signs and in some of the tubes used 

 in television. 



FIG. 44. USES OF RARE GASES OF THE ATMOSPHERE 



What is the nature of burning? It is a familiar ex- 

 perience that the fuel in a stove, a furnace, or a bon- 

 fire will burn best when there is a good draft of air 

 flowing to the fire. Only the oxygen of the air is used 

 in burning, the other gases passing up the chimney 

 unused. 



Oxygen is always needed when anything burns, as 

 burning is simply the \ substance uniting chemically 

 with oxygen to form a new chemical compound. Let 

 us examine some common substances which burn and 

 discover what really happens. Coal is almost pure car- 

 bon, and when it combines with oxygen it does so 

 with such speed that quantities of light and heat are 

 given out and a new substance, carbon dioxide, is 

 formed. The chemist has an interesting way of show- 

 ing this combination in much the same manner as 



FIG. 45. SUBSTANCES BURN AT DIFFERENT RATES 



that in which you would write an equation in mathe- 

 matics. He would write 



carbon + oxygen = carbon dioxide 



Many of you have smelled the odor of burning sul- 

 phur which is sometimes used as a disinfectant. When 

 it burns it also unites with oxygen thus 



sulphur + oxygen = sulphur dioxide 

 It is the sulphur dioxide that has the irritating odor. 



When iron rusts it unites with oxygen in the same 

 way as the carbon and sulphur do. 



iron + oxygen = iron oxide 



The new chemical substance formed when things 

 unite with oxygen is called an oxide. 



There is a difference in the burnings explained 

 above. In the case of carbon and sulphur, it is so 

 rapid that heat and light are also given out. The 

 burning of iron takes place so slowly that the heat 

 produced is not noticed, and the burning is said to be 

 slow, while with the carbon and sulphur it is spoken 

 of as rapid. Very rapid burning takes place whenever 

 anything explodes, for an explosion is simply the very 

 rapid uniting of some substance with oxygen. The 

 great English dirigible R-101, which exploded in 1931, 

 was filled with hydrogen, a very light and highly ex- 

 plosive gas. When hydrogen explodes it unites very 

 rapidly with oxygen, forming hydrogen oxide or 

 water. 



hydrogen + oxygen = water 



Why do plants and animals breathe? To carry on 

 the different activities which living things are called 

 upon to do, such as moving, growing, breathing, and 

 digesting food, it is necessary that they have energy. 

 This is obtained from the food which they eat, but it 

 can be obtained only when oxygen is present to unite 

 with the foods, or slowly burn them, and set free the 

 energy that they contain. This is exactly the same 

 thing that happened to the coal or carbon when it was 

 burned. As it united with the oxygen of the air it gave 

 out the energy, and a new substance, carbon dioxide, 

 was formed. 



Much of the food that we eat for energy purposes, 

 such as sugar and starch, contains carbon. This food 

 is digested and carried by the blood stream to the dif- 

 ferent parts of the body. Air is taken into the lungs 

 and the oxygen is removed by the blood, which takes 

 it to the parts of the body in which energy, is being 

 used, such as the brain or a leg or arm muscle. Here 

 the slow burning takes place, the energy is set free, 

 and carbon dioxide is carried back by the blood to the 

 lungs, where it is passed off as we exhale or breathe 

 out. The simple experiment of blowing the breath 

 through clear limewater demonstrates this fact. 



All living things secure the oxygen which they 

 must have to carry on life and also give out carbon 



