IV 

 EXPLORING THE ATOM 



IF you take a lump of dry salt between your thumb 

 and fingers you may readily reduce it to an im- 

 palpable powder. If you were to dust some of the 

 almost invisible grains of this powder upon a glass 

 slide and examine them through a microscope, you 

 would find that the smallest of the dust-like particles 

 now seems rather like a rough and jagged piece of 

 rock rather than like the infinitesimal thing it ap- 

 peared to the naked eye. It is easy to believe that 

 this fragment of matter is built up of smaller par- 

 ticles and is nowhere near the limits of divisibility. 



If now you put a few drops of water on the slide, 

 you will see the rock-like particle of salt fade away 

 and dissolve into nothingness. It has become abso- 

 lutely invisible. If the microscope you are using is 

 a powerful one, this means that there remains no 

 particle of the salt of the size of one-hundred-thou- 

 sandth of an inch. 



In point of fact, the portion of salt has now been 

 separated into molecules so small that many millions 

 of them must be massed together to form the smallest 

 visible particle of matter. These molecules are in all 

 probability moving about freely among the mole- 

 cules of water, It is not quite absolutely certain as 



SOI 



