290 



Domestic Science 



200. When preparing hydrogen in Experiment 134, 

 the gas was not collected in quantity until a small 

 sample burnt without explosion. The occurrence of 

 an explosion showed that the gas collected was a 

 mixture of hydrogen and air, and not pure, nor nearly 

 pure, hydrogen. The explosion caused by the ignition 

 of this mixture is due to the hydrogen in the test-tube 

 all combining at practically the same instant with the 

 oxygen contained in the air mixed with it. As already 

 mentioned, the combination of these two gases is 

 attended by the liberation of a large quantity of heat, 

 and the enormous expansion caused by the high 

 temperature produced by the heat liberated makes 

 the gases within the test-tube rush out with great 

 violence, and some of the energy generated becomes 

 apparent to our sense of hearing by 

 being transformed into that form of 

 energy which we call sound. The 

 vigorous nature of the explosion may 

 be shown, with perfect safety if the 

 directions are faithfully carried out, 

 by performing 



EXPERIMENT 135. Drop a few 

 pieces of granulated zinc into a soda- 

 water bottle of the shape shown in 

 Fig. 96. Fit the bottle with a cork 

 through the centre of which a hole 

 of about diameter has been bored. 

 Remove the cork, pour in a little 

 hydrochloric acid, and replace the 

 cork firmly in the neck of the bottle. 

 Hold the bottle with a duster 

 wrapped around the hand, and 

 bring the opening in the cork close 



Fig. 96. 



