24 THE ELEMENTS OF PLANT FOOD 



product in the manufacture of illuminating gas in the 

 cities. Ammonia combined with water represents a great 

 class of compounds, called bases, that are the opposite 

 of the acids. 



Nature of a Base. A base is a compound contain- 

 ing O and H, that turns red litmus blue, and neutralizes 

 an acid. 



All acids contain H. All bases contain the hydroxyl 



" radical OH. Acids turn blue litmus red, bases turn red 



p litmus blue. Acids and bases mixed together destroy 



the essential characteristics of each other and form a 



new substance, called a salt, and water. 



An alkali is a base that is soluble in water, combines 

 with fats to form soaps, and has a caustic action on 

 animal and vegetable tissues. 



Ammonium hydroxide is a good illustration of 

 an alkali. 

 ^ Some of the important bases are : 



Ammonia (NHs), when combined with water (NH 4 OH) 

 and then called ammonium hydroxide; potassium hy- 

 droxide (KOH) ; (caustic soda) sodium hydrate (NaOH) ; 

 (lime) calcium oxide (CaO) or with water (CaOH 2 ). 



Test a small quantity of dilute nitric acid (HN0 3 ) 

 by dipping in it a strip of .blue litmus paper. Note 

 that the blue color is turned to a bright red. This is 

 the acid test. Pour into a dish a few drops of ammonia 

 and water (NH 4 OH). Let the part of the litmus paper 

 that has been turned red by the acid touch the ammonia. 

 Note that the red is turned back to the original blue 

 color by the alkali. Pour a few drops of ammonia into 

 the nitric acid and test again with the blue litmus 

 paper. If it still turns the litmus red, continue adding 

 NH 4 OH to the acid and testing with litmus till a mix- 



