106 A YEAR IN SCIENCE 



Characteristics of acids. Much as the acids may 

 vary in their individual qualities, they all possess 

 certain qualities in common. 



They all contain hydrogen. Hydrochloric acid, for 

 example, is composed of hydrogen and chlorine, 

 H + Cl = HC1. Nitric acid is composed of hydrogen, 

 nitrogen, and oxygen, HN0 3 ; and sulphuric acid, of 

 hydrogen, sulphur, and oxygen, H 2 S0 4 . 



They all have a sour taste. 



The most valuable test by which acids may be recog- 

 nized comes from their action upon a certain vegetable 

 substance known as litmus. Paper colored by this 

 substance is known as litmus paper, and it is used as the 

 common test for an acid. Acids turn blue litmus to a 

 red color. 



Bases. Bases are substances with which we do not 

 so frequently come in contact. Mention has already 

 been made of ammonia. In the laboratory the bases 

 most commonly used are sodium hydroxide and potas- 

 sium hydroxide. These are white solids, soluble in 

 water. 



Characteristics of bases. Bases, like acids, have 

 certain distinguishing characteristics. All bases con- 

 tain hydrogen and oxygen. For example, sodium 

 hydroxide contains sodium, hydrogen, and oxygen, 

 NaOH. Potassium hydroxide contains potassium, 

 hydrogen, and oxygen, KOH. 



A solution of a base has a soapy feel and taste. 



