J 892.1 



Ionic Velocities. 



285 



there will be a transference of C ions in one direction and of A ami 



. ions in the other. If A and B are the kations, the colour 



boundary will move with the current, and its velocity will in anv 



case indicate the velocity of the ion causing the change in colour 



The apparatus used (fig. 2) consisted of two vertical glass tubes 



FIG. 2. 



about 2 cm. in diameter, joined by a third considerably narrower, 

 which was bent parallel to the others for the greater part of its 

 length. The longer tube was filled with the denser solution to about 

 the level A, and then the lighter solution was run into the other 

 tube from a burette till it just began to trickle over the shoulder and 

 run down to A. The proper solutions were then run into the two 

 limbs at rates just sufficient to keep the junction at rest. The 

 current was passed from platinum electrodes which could be con- 

 nected with a battery of twenty-six accumulators by means of 

 platinum wires. The corks fitted loosely to allow any gas which 

 might be evolved to escape. 



The junction tube had an effective length of 13'8 cm., which, 

 divided into the total difference of potential, gave the potential 

 gradient. The correction due to changes of density produced by the 

 passage of the current can be shown to be quite negligible. 



u 2 



