II. THE IONS 



THE dissociation of combined elements, and the 

 formation of ions or unattached atoms, and meres* 

 of substances, having an electrical reaction, is brought 

 about by various influences, the best known of which 

 are heat, light, chemical action, electricity, Rontgen 

 and other rays. Almost all dilute solutions contain 

 ions derived from the substance in the solution ; 

 and gases contain some of their elements in the same 

 condition. The dissociation of combined elements 

 under various circumstances has long been known 

 to scientists ; and, in recent years, the theory of 

 ions has been used to explain various phenomena, 

 such as electrolysis. When a strip of pure zinc and 

 a strip of platinum are dipped in acidulated water 

 neither metal will be affected so long as they are 

 unconnected. But if they are connected by a wire, 

 a chemical action takes place between the zinc and 

 acid (e.g. H 2 S0 4 ), oxygen and hydrogen are dis- 

 engaged and an electric current passes along the 

 wire. The gases are disengaged at the electrodes, 

 but not indiscriminately.! The dissociated gases 



* Merus, a, urn: real, pure, genuine; alone, nothing else, 

 without mixture ; that with which nothing is united. 



t It is well known that this is not a simple and direct 

 chemical action, but is a double action, which may be repre- 

 sented by the following equations : 



At the Cathode. At the Anode. 



2H 2 S0 4 =2H 2 +2S0 4 and 



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