Solution and Chemical Action 361 



One of the most interesting and important facts about 

 acids and bases is that if they are put together in the 

 right proportions they turn to salt and water. Strong 

 hydrochloric acid (HC1), for instance, will attack the 

 skin and clothes, as you know ; if you should drink it, 

 it would kill you. Caustic soda (NaOH), a kind of lye, 

 is such a strong alkali that it would dissolve the skin of 

 your mouth in the way that lye dissolved hair in Experi- 

 ment 1 08. Yet if you put these two strongly poisonous 

 chemicals together, they promptly turn to ordinary 

 table salt (NaCl) and water (H 2 0). Or, as the chemists 

 write it : 



NaOH + HCl-^NaCl + H 2 O. 



You can make this happen yourself in the following 

 experiment, using the acid and base dilute enough so 

 that they will not hurt you : 



Experiment in. Although strong hydrochloric acid and 

 strong caustic soda are dangerous, if they are diluted with 

 enough water they are perfectly harmless. You will find 

 two bottles, one labeled " caustic soda (NaOH) diluted for 

 tasting," and 'the other labeled "hydrochloric acid (HC1) 

 diluted for tasting." From one bottle take a little in the 

 medicine dropper and let a drop fall on your tongue. Taste 

 the contents of the other bottle in the same way. It is not 

 usually safe to taste things in the laboratory. Taste only those 

 things which are marked "for tasting." 



Now put a teaspoonful of the same hydrochloric acid into 

 a clean evaporating dish. Lay a piece of litmus paper in 

 the bottom of the dish. With a medicine dropper gradually 

 add the dilute caustic soda (NaOH), stirring as you add it. 

 Watch the litmus paper. When the litmus paper begins to 

 turn blue, add the dilute caustic soda drop by drop until 

 the litmus paper stays blue when you stir the mixture. Now 



