358 Common Science 



combined when the soap is made. This free alkali 

 cleans things well, but it injures hands and clothes. 



When the drainpipe of a kitchen sink is stopped up, 

 you can often clear it by sprinkling lye down it, and 

 then adding boiling water. // you ever do this, stand 

 well back so that no lye will spatter into your face ; it 

 sputters when the boiling water strikes it. The grease in 

 the drainpipe combines with the lye when the hot 

 water comes down ; then the soap that is formed is 

 carried down the pipe, partly dissolved by the hot 

 water. 



When you sponge a grease spot with ammonia, the 

 same sort of chemical action takes place. The am- 

 monia is a base; it combines with the grease to form 

 soap, and this soap rinses out of the cloth. 



The litmus test. To tell what things are bases and 

 what are acids, a piece of paper dyed with litmus is 

 ordinarily used. Litmus is made from a plant (lichen). 

 This paper is called litmus paper. Try the following 

 experiment with litmus paper : 



Experiment 109. Pour a few drops of ammonia, a base, 

 into a cup. Into another cup pour a few drops of vinegar, 

 an acid. Dip your litmus paper first into one, then into 

 the other, and then back into the first. What color does 

 the vinegar turn it? the ammonia? Try lemon juice; 

 diluted hydrochloric acid ; a very dilute lye solution. 



This is called the litmus test. All ordinary acids, if 

 not too strong, will turn litmus pink. All bases or 

 alkalies will turn it blue. If it is already pink when 

 you put it into an acid, it will stay pink, of course ; if 

 it is already blue when you put it into a base, it will 



