95 



Ionic Friction, 



By p. N. Evans. 



The velocity of a moving body is proportional to the impelling force 

 and inversely proportional to the resistance offered by the snrroundings. 

 In the case of dissolved particles moving through a solution the resist- 

 ance is of the nature of friction. 



The movement of ions through solutions may be observed in the 

 diffusion of dissolved electrolytes from positions of higher to those of 

 lower concentrations, and also in the migrations of the ions during 

 the electrolysis of solutions. The impelling force in the first case is 

 the osmotic pressure; in the second, electric tension. The resistance 

 in both cases is the friction against the other particles— mostly those 

 of the solvent. That this resistance or friction is enormous is seen 

 in the force necessary to overcome it— three hundred and two million 

 kilograms will move a gram of hydrogen ions in water with a velocity 

 of one centimeter per second. 



It has been observed that the addition of a non-electrolyte to a 

 solution of an electrolyte increases the resistance to the passage of the 

 electric current. This might be due to either or both of two causes— the 

 number of ions or carriers of the current might be diminished by the 

 non-electi'olyte's causing a partial deionization of the electrolyte, or the 

 resistance of the solution to the migration of the ions— the ionic fric- 

 tion — might be increased. The second of these two hypotheses has been 

 shown to be the correct one when only moderate quantities of the non- 

 electrolyte are added, though the first also becomes appreciable with 

 larger quantities. 



The lines of reasoning and experiment leading to this conclusion have 

 been of two kinds. First, the degree of ionization of the electrolyte 

 in pure water and in water containing the non-electrolyte was deter- 

 mined in the usual way, based on the conductivity at some definite 

 concentration compai'ed with that at infinite dilution and found to be 

 the same when moderate quantities of the non-electrolyte were present. 

 Second, the increase in the resistance to the passage of the electric 



