THE JOURNEYING ATOMS 



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The molecules and atoms and electrons into which 

 science resolves matter are hypothetical bodies which 

 no human eye has ever seen, or ever can see, but 

 they build up the solid frame of the universe. The 

 air and the rocks are not so far apart in their con- 

 stituents as they might seem to our senses. The in- 

 visible and indivisible molecules of oxygen which 

 we breathe, and which keep our life-currents going, 

 form about half the crust of the earth. The soft 

 breeze that fans and refreshes us, and the rocks that 

 crush us, are at least half-brothers. And herein we 

 get a glimpse of the magic of chemical combinations. 

 That mysterious property in matter which we call 

 chemical affinity, a property beside which human 

 affinities and passions are tame and inconstant 

 affairs, is the architect of the universe. Certain ele- 

 ments attract certain other elements with a fierce 

 and unalterable attraction, and when they unite, the 

 resultant compound is a body totally unlike either 

 of the constituents. Both substances have disap- 

 peared, and a new one has taken their place. This 

 is the magic of chemical change. A physical change, 

 as of water into ice, or into steam, is a simple matter; 

 it is merely a matter of more or less heat; but the 

 change of oxygen and hydrogen into water, or of 

 chlorine gas and the mineral sodium into common 

 salt, is a chemical change. In nature, chlorine and 

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