ATOMS 95 



Carbon is one of the few elements of which Kving bodies 

 are composed. Four elements alone compose nearly all 

 that there is to Kving bodies. The others besides carbon 

 are hydrogen, oxygen, and nitrogen. Water is composed of 

 hydrogen and oxygen, while nitrogen forms about four fifths 

 of the air. It would be rash to conclude, however, that 

 living bodies get the hydrogen, oxygen, and nitrogen that 

 they need directly from water and from air. You will find 

 that such is not the case. 



Iron, sulphur, gold, silver, lead, and copper are^ also fa- 

 miliar elements. Of these iron and sulphur are found in 

 living things. 



33. Atoms. — We have spoken of water as an example 

 of a compound. We have also said that the elements 

 hydrogen and oxygen are found in water. The molecule 

 of water is composed of these two elements. Now the 

 question arises, how are the elements arranged in the mole- 

 cules of a compound? If a molecule is the least particle 

 of a compound, what are these least particles of elements 

 of which molecules are composed ? 



To understand this we* must understand something of 

 what happens when molecules are broken up. A molecule 

 of sugar is much larger than a molecule of water. It can 

 be broken up into molecules of water and of other sub- 

 stances. Then the molecules of water can be broken up 

 into molecules of hydrogen and oxygen. This can be done 

 by electricity. But now the reducing process has come to 

 the elements themselves. They cannot be reduced into 

 other substances. Their least particles seem to be reduced 

 as far as reduction can go. To the particles which could 

 not be reduced at all the early scientists gave the name 



