Chemical Change and Energy 301 



and so does the nitrogen; what is left is mainly black 

 carbon. 



Making hydrogen come out of hiding. The light 

 gas, hydrogen, conceals itself as perfectly as carbon 

 does by combining with other elements. It is hiding 

 in everything that is sour and in many things that are 

 not sour. And you can get it out of sour things with 

 metals. In some cases it is harder to separate than in 

 others ; and some metals separate it better than others 

 do. But one sour compound that you can easily get 

 the hydrogen out of is hydrochloric acid (HC1) , which 

 is hydrogen combined with the poison gas, chlorine. 

 One of the best metals to get the hydrogen out with is 

 zinc. Here are the directions for doing it and inciden- 

 tally for making a toy balloon : 



Experiment 91. Do this experiment on the side of the 

 laboratory farthest from any flames or fire. Do not let any 

 flame come near the flask in which you are making hydrogen. 



In the bottom of a flask put two or three wads of zinc 

 shavings, each about the size of your thumb. Fit a one- 

 hole rubber stopper to the flask. Take the stopper out and 

 put a piece of glass tubing about 5 inches long through the 

 hole of the stopper, letting half an inch or so stick down 

 into the flask when the stopper is in place (Fig. 162). With 

 a rubber band fasten the mouth of a rubber balloon over 

 the end of the glass tube that will be uppermost. Fill the 

 balloon by blowing through the glass tube to see if all con- 

 nections are tight, and to see how far it may be expanded 

 without danger of breaking. You can tell when the balloon 

 has about all it will hold, by pressing gently with your fingers. 

 If the rubber feels tight, do not blow any more. Let the air 

 out of the balloon again. 



Now get some hydrochloric acid (HC1) diluted with three 



