34 AMERICAN MANURES. 



The laws that govern. these combinations are 

 arbitrary ; any excess of an element does not 

 affect the composition of the resulting com- 

 pound. 



An Element contains but one kind of matter, 

 as Oxygen, Sulphur, Calcium. 



A Compound is the union of two or more ele- 

 ments ; as Water, Sulphuric Acid, Oxide of Cal- 

 cium. 



An Oxide is a combination of an element with 

 oxygen ; as calcium united with oxygen is called 

 the oxide of calcium, or quick lime ; or sulphur 

 united with oxygen to produce sulphuric acid, 

 is called an oxide of sulphur. The union of 

 oxygen with different elements produces both 

 acids and bases. 



A Salt is the union of an acid with a base, the 

 active properties of the acid being neutralized, 

 and the compound having properties different 

 from either; as lime or the oxide of calcium 

 unites with sulphuric acid to form the sulphate 

 of lime, or land plaster. A salt may also be pro- 

 duced by the union of an element with an ele- 

 ment ; as chlorine uniting with sodium to form 

 common salt. The force that produces the com- 

 binations of dissimilar bodies is termed Chemical 

 Affinity. 



Chemical Affinity may be defined as an 

 attraction exerted at insensible distances between 



