ACIDS, BASES, SALTS, AND NEUTRALIZATION 73 



and base-forming elements. Salts are neutral compounds. 

 In the study of acids, bases, and salts, the character of 

 the compound can always be determined from the formula 

 as Ca(OH) 2 . Calcium hydrate is a base because it con- 

 tains the hydroxyl radical OH. CaCl 2 is a salt because 

 it is composed of the acid-forming element Cl and the 

 base-forming element Ca. HC1 is an acid because it is 

 composed of hydrogen and the acid-forming element Cl 

 and the H can be replaced by a metal. Acids and bases 

 do not exist as such to any appreciable extent in nature. 

 Salts are neutral compounds and the materials most ex- 

 tensively found. In the table, Section 15, the character- 

 istic properties of some of the elements as acid- or base- 

 forming, are given. A few elements, as will be discussed 

 later, have both acid and basic characteristics. 



77. Radicals. A^jradical j s ajgroup ofjslements which 

 enters into chemical Combination like a single element. 

 When three elements combine to form a compound the 

 combination is made in the following way : Two of the 

 elements first form a radical, and then this radical com- 

 bines with the third element. Every radical has its own 

 valence which is independent of that of its separate atoms. 

 A radical can exist only in chemical combination ; it can- 

 not be separated. Its individuality as a radical exists 

 only when in combination. The elements which unite 

 to form a radical do not do so according to the law of 

 valence. There are only a few of the more common 

 radicals which require special study at this stage of the 

 work. Example : When H, S, andO combine, the S and 

 O first form a radical, SO 2 , which has a valence of 2. Two 



