6 THE AIR AND THE GASES IN IT. 



18. What is chemistry ? It is the science which tells 

 us what water, air, soil, and all other things are, what 

 they are made of, and how the elements of which they 

 are made act upon each other ; and a person who studies 

 these things, and makes experiments upon them, is called 

 a chemist. 



CHAPTER II. 



THE AIR AND THE GASES IN IT. 



19. The Air is that which we breathe, and by which 

 we are constantly surrounded. It is very thin and light, 

 and yet it has some little weight. We cannot see it, and 

 yet it is always about us and touching us. The wind is 

 air in motion. We feel the wind, and we may feel the 

 still air when we move our hand rapidly in it ; and we 

 also feel and hear it when we move a stick swiftly 

 through it. 



If I fill a bladder with air, and press it, the bladder 

 yields ; but as soon as the pressure is withdrawn, it swells 

 out again to its former size. This is because the air is 

 springy or elastic. It is essential to burning, or com 

 bustion. Without air, the candle would be extinguished, 

 and the fire would go out. It is not less necessary to the 

 life of man and other animals, and to plants. 



20. The air is composed of a thin fluid or gas, called 

 ori/^ f /?, (which means, producer of acids,) mixed with 

 another air or gas called nitrogen, (producer of nitre,) 

 or azote, (not sustaining life.) The air also contains a 

 gas called carbonic acid, a small but variable quantity of 



