274 MORRIS LOEB 



in its immediate surroundings. This is, of course, an unten- 

 able assumption. Supposing, on the other hand, that only the 

 negative ions were immovable, while the positive ones could 

 travel across the liquid as fast as required to supply the places 

 of those disappearing upon the negative electrode : the liquid 

 would be homogeneous at all moments, and there would be 

 no concentration nor dilution around the electrodes. We can- 

 not, however, assume that the negative ions are immovable, 

 everything showing that they move toward the cathode 

 just as well as the positive ones do toward the anode. If both 

 move [107] with equal rapidity, as was tacitly assumed be- 

 fore Hittorf , a little reflection will show that the liquid about 

 the cathode will lose just half as much metal as is deposited 

 upon the electrode, while half the metal given up by the 

 anode to the surrounding liquid will have been transferred 

 toward the cathode. Hittorf 's laborious analyses proved that 

 none of these three possibilities was fulfilled. The relation 

 between the changes in concentration and the amount of 

 metal transferred from one electrode to the other proved 

 conclusively that the two classes of ions did not move with 

 equal rapidity; and he showed how this ratio provided a 

 measurement of the share of each class in the total movement. 

 For any salt, [the reciprocal of] the ratio of the weight of the 

 metal deposited to the amount of metal lost by the fluid 

 around the cathode (or its equivalent, the amount gained 

 by that around the anode) represents the share of the nega- 

 tive ion, the anion, in the total movement. 



Hittorf has had few followers in these investigations, 1 as 

 the difficulties of experiment were discouraging. Analytical 

 accuracy demanded the use of concentrated solutions, or of 



1 The following list includes all the literature; Hittorf, Pogg. Annalen, 89, 177, 

 98, 1, 103, 1, 106, 337; G. Wiedemann, Ibid. 99, 177; Weiske, Ibid. 103, 466; 

 Kuschel, Wied. Annalen, 13, 289; Kirmis, Ibid. 48, 503; Lenz, M6m.Ac. St. Ptters- 

 bourg, 30, 1882. 



