CH. xxxvii. ELECTRICITY <5r CHEMICAL AFFINITY. 395 



more elements together in one compound substance. You 

 will remember that Bergmann, and indeed Newton before 

 him, pointed out that there is some force which causes 

 certain bodies to choose each other out when they meet, 

 and to unite firmly so as to become a new substance which 

 has its own peculiar characters. Chlorine and sodium, for 

 example, when heated, unite to form common salt, which is 

 not the least like either chlorine or sodium when they are 

 separate ; and in the same way hydrogen and oxygen unite 

 to form water. In these new states they are held together 

 by a power which for want of a better name we call 

 4 chemical attraction,' or * chemical affinity.' 



Now Davy showed that an electric current conquers this 

 power and sets the different elements free, so that they can 

 each go their own way. Thus the electric current passing 

 through the water overcomes the force which holds the 

 oxygen and hydrogen together, so thac, at the point where 

 the battery wires touch the water, hydrogen bubbles come 

 off on one side and oxygen on the other. 



It is to Faraday, however, that we owe most of our 

 knowledge about the intimate connection between electricity 

 and chemical change. He followed Davy's experiments, 

 and traced out very clearly the cause and effect of the 

 chemical current. He showed in the first place that a sub- 

 stance cannot be decomposed by electricity unless it is a 

 good conductor, so that the current passes readily along it. 

 Thus, ice being a bad conductor, the slightest film of ice 

 interposed between the water and the electric wires will pre- 

 vent the current from setting free the oxygen and hydrogen ; 

 and ether and alcohol cannot be decomposed at all by elec- 

 tricity, because they will not conduct the current. 



He also showed that the electric current itself does not 

 depend upon any effect which the two metals have directly 



