362 Common Science 



add a drop or two more of the acid until the litmus turns 

 pink again. Taste the mixture. 



Put the evaporating dish on the wire gauze over a Bunsen 

 burner, and bring the liquid to a boil. Boil it gently until 

 it begins to sputter. Then take the Bunsen burner in your 

 hand and hold it under the dish for a couple of seconds ; re- 

 move it for a few seconds, and then again hold it under the 

 dish for a couple of seconds ; remove it once more, and keep 

 this up until the water has all evaporated and left dry white 

 crystals and powder in the bottom of the dish. As soon as 

 the dish is cool, taste the crystals and powder. What are 

 they? 



Is salt an acid or a base ? 



Whenever you put acids and bases together, you get 

 some kind of salt and water. Thus the chlorine (Cl) 

 of the hydrochloric acid (HC1) combines with the 

 sodium (Na) of caustic soda (NaOH) to form ordinary 

 table salt, sodium chloride (NaCl), while the hydrogen 

 (H) of the hydrochloric acid (HC1) combines with the 

 oxygen and hydrogen (OH) of the caustic soda (NaOH) 

 to form water (H 2 O) . Chemists write this as follows : 



NaOH+HCl->-NaCl+H 2 O. 



Why sour milk pancakes are not sour. It is because 

 bases neutralize acids that you put baking soda with 

 sour milk when you make sour milk pancakes or muffins. 

 The soda is a weak base. The sour milk is a weak acid. 

 The soda neutralizes the acid, changing it into a kind of 

 salt and plain water. Therefore the sour milk pancakes 

 or muffins do not taste sour. 



In the same way a little soda keeps tomatoes from 

 curdling the milk when it is added to make cream of 

 tomato soup. It is the acid in the tomatoes that curdles 



