64 THE ELEMENTS OF PLANT FOOD 



tracts moisture from the air and is readily soluble 

 in water. As a fertilizer it is especially valuable in 

 giving to plants a quick start and for promoting a 

 luxuriant stem and leaf growth. 



Sodium Carbonate (Na 2 CC>3), sal soda, washing soda. 

 -This compound is ordinarily spoken of as soda. 

 It is used in making soap and in the manufacture of 

 glass. It takes the form of crystals when combined 

 with H 2 O. If the H 2 O be driven off by heat, there re- 

 mains a white powder which is pure Na 2 CO3. 



Acid Sodium Carbonate (HNaCO 3 ), bicarbonate of 

 soda, baking soda. --This compound is also some- 

 times called "soda." When treated with an acid it 

 effervesces, releasing CO 2 . Children sometimes make 

 " home-made soda water " by mixing this soda with 

 vinegar. Its chief use is in the manufacture of bak- 

 ing powder. Baking powders are made by combining 

 sodium bicarbonate with some acid salt. When water 

 is added, the reaction takes place and CO 2 is formed. 

 The salt is usually acid potassium tartrate (cream of 

 tartar) (KHC 4 H 4 O 6 ), or acid phosphate. To prevent 

 reaction taking place through the absorption of moisture 

 from the air, some substance like starch is added to the 

 baking powder to keep it as dry as possible. 



Sodium Hydroxide (NaOH), caustic soda, is a white, 

 brittle solid which dissolves in water with the produc- 

 tion of considerable heat. It is a very strong alkali. 

 It is used in various industrial processes, resembling 

 KOH in its action, but is less powerful. An impure 

 variety of sodium hydroxide is sold in cans as " con- 

 centrated lye." 



Note. Borax is sodium bihorate. It is found in nature in several 

 lakes in Asia and in the western part of the United States. The 



