10 AGRICULTURAL CHEMISTRY 



gold. When iron is exposed to moisture and air it rusts, 

 while aluminum is not readily affected by these agents. 

 This is because iron and aluminum have different chem- 

 ical properties. The chemical properties of a substance 

 include the way in which it combines or produces chem- 

 ical change when brought into contact with other ele- 

 ments or compounds. Some elements are characterized 

 as chemically active or inactive. An active element is 

 one that readily unites or combines with other elements, 

 while an inactive or passive element is one that does not 

 readily unite or combine. Some elements are active 

 under certain conditions and with some of the elements, 

 and inactive under other conditions and with other ele- 

 ments. The various elements require different conditions 

 for producing chemical changes. In studying an element, 

 the way in which it deports itself in producing chemical 

 changes, the ability with which it combines with other 

 elements, and the products which are formed as the re- 

 sult of the chemical changes, are some of the more impor- 

 tant chemical properties considered. 



The study of the chemical and physical properties of 

 elements and their compounds is important in many ways, 

 as the value of a substance depends entirely upon its 

 properties. In the growing and cultivation of crops, the 

 production, preparation, and the economic use of foods, 

 the treatment of diseases, and in all manufacturing opera- 

 tions, as the smelting and refining of metals, the chemical 

 and physical properties of the elements and their com- 

 pounds are constantly made use of. 



15. Symbols of the Elements. In the study of chem- 



