OF VITAL PHENOMENA 23 



practice is not to measure the electrodes but to calibrate the cell 

 with a known solution of KC1. 



It is found that the molecular conductivity of an electrolyte 

 increases with dilution, or, in other words, the dissociation in- 

 creases. At infinite dilution the dissociation would be complete, 

 and is practically complete at .0001 mol. 



The question may be asked: Where does the electric charge 

 of the ion come from? The study of radium has shown that 

 the molecule contains a store of electricity but the positive 

 charges exactly equal the negative charges and the molecule 

 therefore is electrically neutral. These charges may exist free 

 from molecules or ions and are then called electrons. It seems 

 probable that negative electrons have no weight. A molecule of 

 NaCl may be represented by an atom of Na and an atom of CI, 

 each with a positive charge, connected by means of two negative 

 electrons. When the molecule dissociates the negative electrons 

 go with the CI atom and give it an excess of one negative charge, 

 whereas the Na atom has a positive charge. 



If an electric current is passed through a solution, anions are 

 deposited on the anode and cations on tihe cathode. It is neces- 

 sary to pass 96500 coulombs of electricity (=1 Faraday) in 

 order to deposit 1 gram equivalent of ions on an electrode. If 

 the ions remain on the electrodes as in electroplating, a gram 

 molecule of the electrolyte is removed from the solution by the 

 passage of 96500 coulombs, for a gram equivalent of anions is 

 deposited on the anode and a gram equivalent of cations on the 

 cathode. In any cross section of the solution, if x gram equiva- 

 lents of anions is moving in one direction, 1 — x gram equiva- 

 lents of cations is moving in the opposite direction. Supposing 

 that the cations move twice as fast as the anions, if we draw an 

 imaginary cross section half way between the electrodes, twice 

 as many 'cations will pass going in one direction as anions going 

 in the opposite direction, or % gram equivalent of cations move 

 to the cathode and Ys gram equivalent of anions to the anode. 

 Around the cathode 1 gram equivalent of cations is removed by 

 the electrode and Y$ is gained by migration, leaving a deficiency 

 of ]/z, whereas Y$ of anions are lost by migration, or, in other 

 words, Yz m °l electrolyte is lost. At the anode Yz m °l electrolyte 

 is lost. The change in concentration of the electrolyte at the 



