IONIC VELOCITIES. 



377 



acid, when the potential gradient is one volt per centi- 

 metre, the hydrogen ion travels with a velocity of '00282 

 centimetres per second, and the chlorine ion with a velocity 

 of '00075 centimetres per second. F. Kohlrausch ( Wiede- 

 mann s Anna/en, vols, vi., xxvi. and 1.) has made a long 

 series of determinations of the conductivity {i.e., the re- 

 ciprocal of the specific resistance) of solutions, and used the 

 numbers obtained to calculate the ionic velocities. He ex- 

 presses his results in terms of " molecular conductivity " — 

 i.e., conductivity (/c) divided by strength of solution in gram- 

 equivalents per litre (m). This corresponds to 



1000NV 



in our equation (i.) (since N is the concentration referred 

 to cubic centimetres), so that we get 



k_ 



111 



O'OOOIO^s /t. /•• x 



V = u -- v = —^ — — = o'io35 x - - • ... (11.) 



Nr 



He finds that as the solutions become more dilute, the 

 molecular conductivities, and, therefore, the velocities of 

 the ions, in general increase, but that in most cases they 

 come to a limit which enables him to determine either by 

 exterpolating in a formula, or by drawing a curve, the value 

 of the velocity corresponding to infinite dilution. Thus the 

 most recent values for sodium and lithium chlorides ( Wied. 

 Ann., 1893, 1- 7' 4°3) are the following, where u is the 

 velocity of the kation, and v that of the anion, each in io~ 6 

 centimetres per second, while vi is the concentration in gram- 

 equivalents per litre : — 



