METHODS OF ELECTRICAL STIMULATION 31 



Views of Arrhenius. It was Arrhenius who 

 made these ideas regarding the dissociation of 

 the molecules of solutions into ions quantitative 

 and thus precise. Feeble electrolytes, i. e. poor 

 conductors of electricity, are but slightly dis- 

 sociated, whereas solutions that readily conduct 

 electricity are largely dissociated. lonisation 

 may be measured by the degree of conductivity. 

 Undissociated molecules carry no electricity. Each 

 univalent ion has the same load : 96,500 coulombs. 



Conductivity depends on the number of the 

 ions and upon their speed. In this connection 

 the following observation is of interest. If suc- 

 cessive quantities of pure water be added to a 

 salt solution, the conductivity will increase as 

 the dilution increases. The first factor to be 

 considered here is the viscosity of the solution, 

 for the viscosity determines the resistance of the 

 solution to the passage of ions, and thus determines 

 the speed of the ions. As the addition of water 

 continues a point is soon reached at which the 

 amount of water in the solution is so great in 

 relation to the amount of salt that the water may 

 be regarded practically as pure. The addition 

 of more water should not then appreciably affect 

 the viscosity and thus the speed of the ions. If 

 the conductivity were related solely to the speed 

 of the ions, the conductivity should not then 



