4 AGRICULTURAL CHEMISTRY 



ble to farther division by purely physical methods. The 

 smallest particle of a material that can exist and have all 

 of the properties of the original material is called a mole- 

 cule. Molecules, however, have never been separated as 

 individuals. All forms of matter are composed of mole- 

 cules. The proof that matter is composed of molecules 

 is founded upon the laws of physics. The reasons for 

 the acceptance of the molecular structure of matter can- 

 not be profitably undertaken by the student of elemen- 

 tary chemistry, but properly form a very important part 

 of advanced chemistry. The molecular structure of 

 matter has been sufficiently well established to warrant 

 the use of the term molecule by the student of elemen- 

 tary chemistry. 



6. Atoms. Whenever a chemical change takes place, 

 the molecule is changed in composition. When an elec- 

 tric current is passed through water, the molecules of 

 water are split up into simpler forms of matter. It is 

 evident that the molecule is not the simplest form of mat- 

 ter, and that while the molecule is the smallest part of a 

 substance, it is, in turn, made up of still smaller parts. 

 These parts of matter which make up a molecule are called 

 atoms. An atom is the smallest part of an elementary 

 substance that can enter into combination to form a 

 molecule. Atoms never exist in nature in a free or un- 

 combined state, but unite to form molecules, and mole- 

 cules in turn unite to form masses. 



7. Elements. The simplest forms of matter, as iron, 

 copper and sulfur, from which it is impossible to extract 

 or obtain simpler bodies, are called elements. The ele- 



