The Romance of Chemistry 717 



another, a complete explanation of such phenomena will only 

 be possible when we know the detailed structure of the atoms 

 and the nature and magnitude of the forces between them. 1 



It is well known to everybody that the atom of one chemical 

 element may combine with one or more atoms of another element. 

 When the chemist speaks of the valency of an element, he means 

 the number of other atoms, with which one atom of this element 

 can directly combine. For example, one atom of hydrogen com- 

 bines with one atom of chlorine, and the result is hydrochloric acid ; 

 or one atom of oxygen will combine with two atoms of hydrogen 

 and the result is water ; one atom of nitrogen combines with three 

 of hydrogen, and we get ammonia. 



These combinations are usually graphically expressed thus: 



Each of these combinations represents a chemical process, 

 that is to say, a chemical change which produces a substance 

 which is totally distinct, not a substance which merely partakes 

 of the characters of the two component elements. 



Thus are the various substances built up; the elements are 

 mostly found in mutual combinations, and the combinations are 

 sometimes of course, very complex. While a particle, or mole- 

 cule, of water consists of two atoms of hydrogen and one of 

 oxygen, the molecule of the proteid called "albumen" is built 



'Sir Ernest Rutherford. 



