IONS CONDUCT ELECTRICITY 17 



The ions which convey positive electricity or are 

 positively electrified travel to the cathode or negative 

 electrode during electrolysis, and are cations or 

 positive ions ; they include hydrogen and the 

 metals. Ions which convey negative electricity 

 travel to the anode or positive electrode, and are 

 called anions ; they include most of the metalloids 

 and non-metals. Cations consist for the most part 

 of a single element, e.g. Na, H, K, Li, Pb, Cu, Fe 

 or Bi. But many anions are compounds of two 

 or more elements, e.g. OH, N0 3 , C10 3 , C 2 H 3 2 , 



so 3 , CA, po 4 . 



All ions do not convey an equal amount of 

 electricity, but their capacity varies with the valency 

 of the atoms. A unit has been established whereby 

 this capacity may be measured ; the ions of 

 1 gramme-molecule of hydrogen will convey an 

 amount of electricity which is equivalent to 96,550 

 coulombs ; and the ions of all monovalent elements 

 carry an equal amount of electricity, the ions 

 of divalent elements twice that amount, and so on. 

 The molecular conductivity of any liquid, however, 

 depends upon the degree of dissociation, for it is 

 the ions alone in any solution which convey elec- 

 tricity, the undissociated molecules being inoperative. 

 The molecular conductivity is increased up to a 

 certain point by dilution of the liquid, which is due 

 partly to the greater rapidity of migration of the 

 ions and partly to the formation of a greater number 

 of ions in the solution. The more a fluid is diluted 

 so much the greater is the ionisation and rate of 

 molecular conductivity up to a certain point ; when 

 this point is reached there is no further increase in 



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