16 GENERAL SCIENCE 



solution, until the litmus paper turns blue. Take a 

 dropper, made out of a small glass tube, and put in 

 acid drop by drop until the litmus begins to turn 

 red. If you get in too much acid, use a small drop 

 of the base. When the solution is neutral the litmus 

 paper will have a bluish-red color. When you think 

 the solution is neutral, put in a few drops of phenol- 

 phthalein, which will remain colorless if the solution is 

 neutral or if it has an excess of acid. If there is the 

 least excess of base, the phenolphthalein will turn red. 



From our study of acids and bases we learned that 

 they will corrode or rust metals, discolor clothing, and 

 even eat a hole in it. But none of these three things will 

 be done by a neutral substance or a substance almost 

 neutral. The three unfavorable effects of strong bases 

 will show us why they cannot be used generally for 

 washing clothing or bathing. So a milder cleansing 

 agent, namely soap, which will remove the dirt without 

 injuring the clothing, has been made. 



14. How Soap is Made. Fats or oils taken from 

 plants or animals, and a base (soda lye or potash lye) 

 are used in soap making. Fats are salts in which 

 glycerine acts as the base and stearic, palmitic, and 

 oleic acids act as acids. When fats are heated with 

 caustic potash (KOH), glycerine is formed and set free, 

 while the potassium of the potash unites with the acids 

 of the fat and forms a salt called soap. The oxygen and 

 hydrogen of the caustic potash help to form the free 

 glycerine. The soaps made with caustic potash are soft 

 soaps. When fats are heated with caustic soda (NaOH), 

 glycerine is formed and set free, while the sodium unites 

 with the acids of the fat and forms hard soap. Hard 

 soap can also be made by using potash lye, if common 



