Science progress. 



No. 5. July, 1894. Vol. I. 



IONIC VELOCITIES. 



IF a current of electricity be passed through the solution 

 of a metallic salt, decomposition generally occurs, and 

 the products appear at the electrodes where the current 

 enters and leaves the liquid. Since the intervening solu- 

 tion is unaltered, we must suppose that a continual passage 

 of the parts of the salt in opposite directions is going on, 

 the molecules being split up and reformed as their con- 

 stituent atoms change partners. The atoms thus travel 

 through the solution, and are hence called "ions" — kations 

 or anions as they travel with or against the current. Thus 

 in a solution of hydrochloric acid the hydrogen travels with 

 the current and appears at the kathode, while the chlorine 

 moves in the opposite direction and is set free at the anode. 

 An account of the investigations which have been made on 

 this motion of the ions, and on the velocities with which 

 they travel, is the subject of this article. 



We must first consider whether it is possible to calculate 

 these velocities from the electrical properties of solutions. 

 Faraday discovered that the passage of a definite quantity of 

 electricity liberated a mass of a certain element which was 

 proportional to the chemical combining weight of that element 

 — not to its atomic weight, but to its atomic weight divided by 

 its valency. Thus the passage of one unit (on the centimetre- 

 gram-second system) of electricity liberated o'oooio35 gram 

 of hydrogen, and o'oooio35 x 35'4 gram of chlorine from a 



solution of hydrochloric acid or o'OOOi035 x 10S gram of 



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