OXYGEN 



91 



be no fire ; there could be no water ; there could be no 

 life, and the earth would be a barren waste. 



Preparation. One of the simplest ways to obtain 

 oxygen is to separate it from some compound in which 

 it is found, and collect the gas by doAvnward displace- 

 ment of water. This is done by inverting large mouth 

 bottles filled with water over the bridge in a pneumatic 



Fig. 39. Preparation of oxygen. A mixture of potassium 

 chlorate and manganese dioxide is being heated in the flask. 

 The gas passes out through the delivery tube and collects in 

 the bottles. 



trough which is filled with water to a depth just cover- 

 ing the bridge. A tube leads from the flask containing 

 the compound, to the mouth of the bottle under the 

 water. As the compound is broken up and the oxygen 

 separated from it, usually by the application of heat, 

 the gas being much lighter than water rises into the 



