CHAPTER III 



THE COMPOSITION OF MATTER 



Here is an interesting fact. If you were asked to make 

 a list of the materials found in the things you see about 

 you every day, it would take hours and hours, and the list 

 would be very, very long. But if a scientist gave you a 

 list of all the basic kinds of matter in the world, there 

 would be only about ninety. How is that? How can there 

 be only ninety kinds of original matter and thousands of 

 materials? 



The Molecular Theory. Through their study and experi- 

 ments scientists have learned some startling things about matter. 

 They have worked out what is known as the molecular theory 

 which tells us that substances are made up of countless tiny par- 

 ticles or bits of matter. The very smallest bit into which a sub- 

 stance can be broken up and still be the same kind of substance, 

 they call a molecule. 



A molecule is so small that it cannot be seen even with the 

 aid of the microscope, and no scales are fine enough to weigh it. 

 Moreover, these molecules are never still. They are always in 

 continuous motion or vibration one against another even in the 

 hardest of materials. The rate at which these molecules vibrate 

 varies with the temperature. The more an object is heated, the 

 faster these molecules vibrate. 



The Atomic Theory. Most substances are made up of 

 different kinds of material. When a molecule of such a sub- 

 stance is broken up into particles of the material of which it is 

 composed these particles are called atoms. These atoms are not 

 like the molecules from which they are taken. 



The atomic theory was formed in the beginning of the 

 nineteenth century by John Dalton, an Englishman, though 

 the idea had long existed in a crude way in the minds of 

 thinking men. The theory assumes that atoms of the same sub- 

 stance have the same weight and that different kinds of atoms 



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