378 



SCIENCE PROGRESS. 



The numbers obtained for the same ion in various salts 

 are found to differ while the solutions are strong, but to 

 approach as dilution goes on, and finally to become identical 

 when the limit is reached. This is clearly shown by the 

 preceding table in the case of chlorine, the values for which 

 in sodium and lithium chlorides are given in the columns 

 under the heading v. Kohlrausch was thus enabled to 

 assign to each ion a specific ionic velocity, which, when the 

 dilution is infinite, is independent of the nature of the other 

 ion or ions present. The following are some of his latest 

 values : — 



These numbers are calculated for a potential gradient of one 

 volt per centimetre and a temperature of i8°C. 



It is interesting to observe the magnitude of the forces re- 

 quired to drive the ions with a certain velocity. If we have a 

 potential gradient of one volt per centimetre, the electric 

 force is io 8 in C.G.S. units. The charge of electricity on one 

 gram-equivalent of any ion is i/'oooio35 = 9653 units, 

 hence the mechanical force acting on this mass is 9653 x io 8 

 dynes. This produces (suppose) a velocity u, then the 



force required to produce unit velocity is P A = - — — 



u 



dynes = - — — kilogram weights. If the ion have an 



equivalent weight A, the force producing unit velocity when 



acting on one gram is P x = 9-84 x io 5 x -r — kilogram weights. 



A u 



In the case of potassium this gives to the force acting on 



one gram in very dilute solution a value equal to the weight 



of 38,000,000 kilograms. Since the velocity is uniform it 



follows that the frictional forces are equal and opposite to 



this, and collecting all such opposing forces under the name 



