56 PRINCIPLES OF CHEMISTRY. 



3. "When acted upon by acids, they form salts. For instance: 

 Potassium hydrate is a base ; when brought in contact with 

 hydrochloric acid it forms the salt potassium chloride and water, 



KHO + HCl = H 2 + KC1. 



Neutral substances. All substances having neither acid nor 

 basic properties are neutral. Water, for instance, is a neutral 

 substance, having no acid or alkaline taste, and no action on 

 red or blue litmus. Many neutral substances, to some extent 

 even water, appear to possess the characteristic properties of 

 both classes, acids and bases; of neither class, however, to a 

 very great extent. 



Salts. A salt is a compound formed by the union of an acid 

 and a base (usually with the simultaneous formation of water), 

 or by the action of an acid on a metal (usually with the libera- 

 tion of hydrogen). 



According to the number of hydrogen atoms replaced in an 

 acid, we distinguish neutral and acid salts. A neutral salt is 

 one formed by replacement of all the replaceable hydrogen 

 atoms of an acid. For instance : KC1, K 2 S0 4 , K 3 P0 4 . (As 

 monobasic acids have but one atom of hydrogen which can be 

 replaced, they form neutral salts only.) 



Acid salts are acids in which only a portion of the replaceable 

 hydrogen atoms has been replaced. For instance : KHS0 4 , 

 K 2 HP0 4 , KE 2 P0 4 . 



Double salts are salts formed by replacement of hydrogen 

 in an acid by more than one metal. For instance : KiS[aS0 4 . 



Residue, radical or compound radical, are expressions for un- 

 saturated groups of atoms known to enter as a whole into dif- 

 ferent compounds, but having no separate existence. For in- 

 stance : The bivalent oxygen combines with two atoms of the 

 univalent hydrogen, forming the saturated compound H 2 O, 

 water. If we take from this H 2 one atom of H, there is left 

 the group of atoms HO, consisting of an atom of oxygen in 

 which but one point of attraction is actually saturated, the 

 second one not being provided for. 



This group, HO, is a residue or radical, and is known to 

 enter into many compounds; it is, for instance, a constituent of 



