Chemical Change and Energy 303 



FIG. 163. ' Adding more acid without losing the gas. 



If the bubbles do not form rapidly, ask the teacher to 

 pour a little strong hydrochloric acid into the flask ; but 

 this will probably not be necessary. Let the balloon keep 

 filling until it is as large as you blew it. But if the bubbles 

 stop coming before it gets as large as that, close the neck of 

 the balloon by pinching it tightly, and take the stopper out. 

 Let some one add more zinc shavings and more acid to the 

 flask; put the stopper back in, and stop pinching the neck 

 of the balloon. In this and all other experiments when you 

 use strong acids, pour the used acids into the crockery jar that 

 is provided for such wastes. Do not pour them into the sink, 

 as acids ruin sink drainpipes. 



When the balloon is full, close the neck by slipping the 

 rubber band up from the part of the neck that is over the 

 glass tube on to the upper part of the neck. Pull the balloon 



