4,66 



Dr. F. G. Donnan on the 



field everywhere uniform. The effect of the ponderomotive 

 forces on the moving ions in the magnetic field is to urge 

 both positive and negative ions in the positive direction of z. 

 The moving ions will thus acquire component velocities in 

 this direction, and these velocities being in general different 

 for each sort of ion, the result is the separation of positive 

 and negative charges, whereby a potential-gradient is set up 

 in the direction of the z-axis which reduces the originally 

 unequal velocities to equality. We thus obtain a flow of 

 ionic matter in the positive z-direction. This produces in 

 its turn a reverse osmotic gradient or concentration-fall both 

 for dissociated and undissociated salt. The stationary state 

 is finally attained when the net flux of ionic matter in the 

 positive direction of z is balanced by the flux of undissociated 

 salt in the opposite direction. 





3»- 



/ 





Primary 



~*~ Current 



Let J = current-density of primary current, 



c = concentration ( in mols.) of positive plus negative 

 ions, 

 p = corresponding osmotic pressure, 

 0= concentration (in mols.) of undissociated salt, 

 P= corresponding osmotic pressure, 

 u, v= velocities in centim. per second acquired under 

 unit force by one gram-mol. of positive and 

 negative ionic matter respectively, 

 G= velocity acquired under unit force by one gram- 

 ^ mol. of undissociated salt, 



-j— = potential-gradient of primary current, 



de 



■J2 -- potential-gradient of Hall -effect, 



