DISCOVERY OF IONS. 



49 



conductivity for the time taken by it to travel from the 

 flame all the way to the electroscope. 



We may now suppose ourselves seeking help from the 

 chemist. " Why/' he will say ; " the gas from the flame 

 contains nothing but carbonic acid and water. There is 

 nothing remarkable in such things." 



"Very true/' we say; " but it contains conductivity" 



11 Conductivity is a condition/' he will reply, " not a 

 thing." 



But are we sure of that ? Let us filter the gas from the 

 flame through a wad of glass wool before it arrives at the 



To Pump 



Fig. 9. Apparatus for showing that the air retains its conductivity. 



electroscope, or let us bubble it through water, instead. If 

 this be done very carefully, the astonishing result be- 

 comes evident that every trace of conductivity is re- 

 moved ! And pursuing our experimentation, we discover 

 that the conductivity may be removed, as well, by mak- 

 ing the gas traverse a space through which a current of 

 electricity is passing. 



The explanation, then, is clear. The conductivity can- 

 not be a mere condition. If we can blow the conducting 

 air about from one place to another, and if, moreover, we 

 can filter it free from conductivity by passing it through 

 wool or bubbling it through water, it is obvious enough 

 4 



