WHAT IS ELECTRICITY? 201 



and the chlorine gas into chlorions. These are substances 

 with quite different physical and chemical properties from 

 the metal sodium and the gas chlorine. 



On dissolving in a little water, some of the chlorions 

 and sodions, but only a few, become separated ; however, 

 if water be added so as to dilute the solution, a larger and 

 larger number separate, until at a sufficient dilution all 

 are separated. In fact, if this conception be extended, 

 all chemical combinations should be regarded as the 

 transference of electrons from one set of elements to 

 another. 



But not all compounds are split into ions when they 

 are dissolved; it may be conjectured that in the case for 

 instance of such a compound as sugar, which dissolves in 

 water as such, the atoms of carbon, hydrogen, and oxygen, 

 of which it consists, have interchanged electrons, otherwise 

 chemical combination would not exist ; but that the ions 

 do not part from each other, even when opportunity is 

 given by dissolving the sugar in water. 



Although facilities for motion in many cases lead to 

 separation of ions, it does not follow that when facilities 

 are present separation will always take place. 



When common salt is melted, which takes place if it be 

 heated to redness, the ions separate ; that this is the case 

 is proved by its being then able to conduct electricity. 

 Melted glass is also a conductor, although solid glass is 

 not ; and the reason again is probably in the fact that the 

 ions have no freedom of motion in the solid. 



These considerations, however, though closely connected 

 with the nature of ions, are not in such close touch with 

 the subject of this essay, the motive power of electricity. 

 Perhaps a last analogy may make the explanation which 

 I have tried to give somewhat clearer ; it is this : 



Place a dilute solution of salt in one vessel and a 

 concentrated solution in another ; cover both vessels with 



