48 PRACTICAL FARM CHEMISTRY. 



where different elements have the same initial letter 

 a small letter is added. Thus 



The meaning of the letter or character, however, 

 does not end with this. It does not merely repre- 

 sent the substance or element, but also indicates 

 a certain quantity of it — and this quantity is the 

 atom — the ultimate unit of the chemist, and the 

 smallest imaginary particle of the element in ques- 

 tion. Such an atom is indivisable, unchangeable 

 and indestructible. 



The atom is the smallest quantity of an elemen- 

 tary substance that can enter into a chemical com- 

 bination with other atoms. A group of such chemi- 

 cally combined atoms forms a molecule, which is the 

 smallest imaginary particle of a compound sub- 

 stance. Such molecule is subject to many changes. 

 Under the term "chemical analysis" we understand 

 the process of tearing a molecule asunder for the 

 purpose of discovering its component atoms. 



Now the atoms of all these elements, when enter- 

 ing combinations, have a fixed relative weight. 

 The hydrogen atom (H) being the lightest, its 



