ELECTROLYTIC DISSOCIATION 245 



molecule formed two "ions," one, the anion, being 

 abnormal by an additional electron, and the other, the 

 cation, abnormal by a corresponding deficiency. The 

 anion of an electrolyte is not a discrete electron as in 

 metals, nor is it formed by the addition of an electron 

 to one of the original normal molecules as is sometimes 

 the case in gases. In electrolysis both ions are mo- 

 lecular (or atomic) in size and in composition except 

 for the abnormality in number of electrons. More 

 than two ions may be formed from complex molecules, 

 but only in a few of the simplest cases is the number 

 equal to the number of atoms in the molecule. In 

 general it is less than the number of atoms composing 

 the normal molecule. 



Consider, for example, hydrochloric acid. The pure 

 acid and pure water are non-conducting, but a mixture 

 of the two is conducting. This may be observed in a 

 simple manner by inserting two chemically inert elec- 

 trodes, e.g. platinum, and connecting a battery and a 

 current-measuring instrument to the electrodes. Hy- 

 drogen gas will rise from the electrode connected to 

 the negative terminal of the battery, that is, from the 

 cathode. Chlorine gas will rise from the anode. We 

 therefore conclude that the dissociation which has made 

 conduction possible is that of the HC1 rather than of 

 the H 2 O of the solution. The gases which rise are the 

 diatomic gases H 2 and C1 2 and are composed of normal 

 molecules. 



This simple experiment raises four questions : (1) 

 What causes the dissociation which is evidenced by the 

 conductivity of the solution? (2) How do the anion 

 and the cation neutralize their respective abnormal- 



