304 Common Science 



off the glass tube and pinch the neck firmly shut. Take the 

 stopper out and rinse the flask several times with running 

 water. Any zinc that is left should be rinsed thoroughly, 

 dried, and set aside so that it may be used again. Now tie 

 one end of a long thread firmly around the mouth of the 

 balloon and let the balloon go. Does it rise? If it does not, 

 the reason is that you did not get it full enough. In that 

 case make more hydrogen and fill it fuller, as explained above. 



Here is another experiment with hydrogen : 



Experiment 92. Put a wad of zinc shavings, about the 

 size of the end of your little finger, into the bottom of a test 

 tube. Cover it with hydrochloric acid (HC1) diluted one 

 to three, as in the preceding experiment. After the bubbles 

 have been rising for a couple of minutes, take the test tube 

 to the side of the laboratory where the burners are, and 

 hold a lighted match at its mouth. Will hydrogen burn? 



Remember that the hydrogen which the zinc is driv- 

 ing out of the acid is exactly the same as the hydrogen 

 you drove out of water with an electric current. There 

 is a metal called sodium (Na) and another called potas- 

 sium (K) which are as soft as stiff putty and as shiny as 

 silver; if you put a tiny piece of sodium (Na) or potas- 

 sium (K) on water, it will drive the hydrogen out of the 

 water just as zinc drove it out of the acid. The action 

 is so swift and violent and releases so much heat that 

 the hydrogen which is set free catches fire. This makes 

 it look as if the metal were burning as it sputters around 

 on top of the water. There is so much sputtering that 

 the experiment is dangerous; people have been blinded 

 by the hot alkaline water spattering into their eyes. So 

 you cannot try this until sometime when you take a 

 regular course in chemistry. 



