PREPARATION OF OXYGEN. 79 



new attraction we call chemical affinity, or the 

 force of chemical action between different 

 bodies ; we are now no longer concerned with 

 the attraction of iron for iron, water for water, 

 wood for wood, or like bodies for each other as 

 we were when dealing with the force of cohesion ; 

 we are dealing with another kind of attraction, 

 the attraction between particles of a different 

 nature one to the other. Chemical affinity 

 depends entirely upon the energy with which 

 particles of different kinds attract each other. 

 Oxygen and hydrogen are particles of different 

 kinds, and it is their attraction to each other 

 which makes them chemically combine and 

 produce water. 



I must now show you a little more at large 

 what chemical affinity is. I can prepare these 

 gases from other substances as well as from 

 water ; and we will now prepare some oxygen ; 

 here is another substance which contains oxygen 

 chlorate of potash ; I will put some of it into 

 this glass retort, and Mr. Anderson will apply 

 heat to it : we have here different jars filled with 

 water, and when by the application of heat the 

 chlorate of potash is decomposed, we will dis- 

 place the water, and fill the jars with gas. 



