ELECTROLYTIC DISSOCIATION 255 



parently discrete phenomena. The number of laws 

 and concrete facts which the student of science needs 

 to remember are fewer than the names which have 

 become associated with them in their evolutionary de- 

 velopment. If the reader obtains a correct concept of 

 molecules, atoms, and electrons, many important laws 

 will appear to him as deducible. 



In electrolysis the number of electrons leaving the 

 solution at the anode is equal to that entering at the 

 cathode. In conduction through an electrolytic solu- 

 tion it may however happen that the anion and the 

 cation move through the solution at different speeds. 

 The result will be a different concentration of anions 

 near the anode than of cations at the other electrode. 

 This is evidenced in cases like that of copper sulphate 

 CuS0 4 by a paling of the color near the anode, but it 

 may always be found by a chemical analysis of samples 

 of the liquid taken from near the two electrodes. 



In a dilute solution, where dissociation is essentially 

 complete, we should expect the behavior of an ion to 

 be characteristic and not dependent upon the par- 

 ticular substance from which it was derived. Thus 

 all hydrogen ions are alike whether they are obtained 

 from HC1, HNO 3 , H 2 S0 4 , or some other acid. The 

 molecular conductivity of a dilute solution will, there- 

 fore, depend upon the individual characteristics of its 

 anion and its cation. Since the amount of electricity 

 transferred across a solution is the sum of that trans- 

 ferred by the two kinds of ions, the conductivity 

 should be the sum of the conductivities of the two 

 kinds of ions. These conductivities are called their 

 "mobilities." Now, an acid is an electrolyte which 



