CHAPTER XXI 

 ACIDS, BASES AND SALTS 



122. Nature of Acids. The most characteristic thing about 

 acids is their sour taste. In addition, they have the peculiar 

 property of turning certain vegetable juices red or pink. Blue 

 flowers often become pink in the presence of dilute acids, and 

 the change from pink buds to blue flowers is frequently due to 

 the change in the acid contents of the cells. The familiar test 

 for acids is litmus paper, made by soaking paper in a solution 

 derived from a kind of plant called a lichen. All acids redden 

 blue litmus paper. Another test for acids is to add them to 

 carbonates, such as limestone or baking soda. With such sub- 

 stances, they produce a bubbling or effervescence, due to the 

 carbon dioxide released. All acids contain hydrogen and all 

 dissolve in water. Acids are very generally distributed 

 throughout the plant and animal kingdom. Among the com- 

 monest, are malic acid found in apples, citric acid in lemons, 

 acetic acid in vinegar, tartaric acid in grapes, oxalic acid in 

 rhubarb, lactic acid in sauerkraut and sour milk, hydrochloric 

 acid in the stomach of many animals, and carbonic acid in the 

 bodies of both animals and plants. Certain other acids are 

 sometimes known as mineral acids. Among these are nitric, 

 sulphuric, phosphoric, and hydrochloric acids. The last named 

 is commonly known as muriatic acid. 



123. Bases. In many ways, bases are the opposites of 

 acids. This is especially true of their reaction with litmus 

 paper, since they turn red litmus paper blue. Instead of being 

 sour, they usually have a bitter taste, and, when dissolved in 



10 145 



