Solution and Chemical Action 351 



503. Glowworms and fireflies can be seen on the darkest nights. 



504. A lake looks gray on a cloudy day and blue on a clear day. 



505. Dried fruit will keep much longer than fresh fruit. 



506. If you scratch a varnished surface, you can rub the scratch 



out completely by using a cloth wet with alcohol. 



507. Soda is usually dissolved in a little water before it is added to 



a sour-milk batter. 



508. Iron rusts when it gets wet. 



509. Peroxide is usually kept in brown bottles. 



510. Dry lye may be kept in tin cans, but if the lye is moistened 



it will eat the can. 



SECTION 54. Acids. 



Why are lemons sour? 

 How do acids act? 



Some acids are very powerful. There is one, called 

 hydrofluoric acid, that will eat through glass and has to 

 be kept in wax bottles; and all acids tend to eat or 

 corrode metals. You saw what hydrochloric acid did 

 to the zinc shavings when you wanted to make a balloon ; 

 or, to be more accurate, you saw what the zinc shavings 

 did to the acid, for the hydrogen gas that bubbled off 

 was driven out of the acid by the zinc. Then the zinc 

 combined with the rest of the acid to form what chemists 

 call a salt. 



If we were to let the soft metal, sodium, act on hydro- 

 chloric acid, we should get hydrogen also ; but the salt 

 that formed would be regular table salt (NaCl). You 

 cannot do this experiment, however, as the sodium 

 does its work so violently that it is dangerous. 



Experiment 105. To be done by the teacher before the class. 

 If acid spatters on any one's skin or clothes, wash it of im- 

 mediately with ammonia or a strong soda solution. 



