170 INTRODUCTION TO GENERAL SCIENCE 



a. Put some grease on four pieces of the cloth and try to 

 remove it by gasoline, benzine, turpentine, and ammonia 

 water. Arrange the solvents in the order of their rapidity of 

 action. 



b. Put some black and red ink spots on one cloth, and allow 

 it to dry. Repeat with a second cloth, but try oxalic acid 

 at once, on the black spot, and ammonia, or ether, on the red 

 spot. After the first becomes dry, try to remove the spots by 

 the same method. Should spots be removed at once? 



c. Put paint on a cloth and allow it to dry. Put some more 

 paint on another cloth and try to remove it, at once, with 

 turpentine or benzine. Next day try to remove the dried 

 paint. Conclusions ? 



d. Put some iron rust on a piece of cloth and try to remove 

 it with the 5 per cent solution of hydrochloric acid. Do not 

 remove the hydrochloric acid from the cloth, and note how 

 rotten the cloth becomes after a week's time. 



121. ACIDS, BASES, AND SALTS NEUTRALIZATION 



Science classifies matter according to its known effect upon 

 certain other kinds of matter. One of these test substances 

 is litmus, a vegetable product. Certain materials cause blue 

 litmus to turn red; we call them acids: others cause red lit- 

 mus to turn blue; those are named bases. When litmus turns 

 red, we call it an acid reaction; if it turns blue, we call it an 

 alkaline reaction. Phenolphthalein is another test. Acids 

 have no effect on it, but bases turn it red, after which acids 

 will remove the color. 



Acids all contain hydrogen, which may be set free from 

 some acids by means of metals. See Section 114, Composi- 

 tion of Water. Bases all contain at least one part of hydro- 



