SOME CHEMICAL CONCEPTS 



121 



eighty in number, and only a few of them are widely 

 distributed. About a score of them are concerned 

 with the life of man and animals. These substances, 

 however, are found combined in all sorts of different 

 ways, and to study them intelligently it is necessary 

 to know exactly how they are built up. Take, for 

 instance, such a substance as starch. A single grain 

 or molecule of starch may be considered without 

 serious error from our standpoint as containing 

 6 unit grains or atoms of Carbon, 10 unit grains or 

 atoms of Hydrogen, and 5 unit grains or atoms of 

 Oxygen. If 2 unit grains or atoms of Hydrogen, 

 and i unit grain or atom of Oxygen are added to it, 

 the starch becomes sugar. All this clumsy state- 

 ment is stated in the language of the chemist in the 

 simple equation : 



C 6 H 10 5 +H 2 = C 6 H 12 6 . 



The mysterious symbols of chemistry are in most 

 cases the first letter or the first two letters of the 

 name of the element. Thus, Carbon is written C, 

 and Calcium, to differentiate from it, Ca. In 

 some instances the symbols are derived from the 

 Latin names. Thus, Iron (Ferrum), Fe, etc. The 

 elements with which we are concerned in agriculture 

 (with their symbols) are the following : 



