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PROCEEDINGS OF THE AMERICAN ACADEMY. 



Figure 1. J. is the plate, and its resistance can be assumed to remain 

 fairly constant, except for its temperature coefficient. This factor has 

 a small value within the range of practical operating conditions. C is 

 that part of the electrolyte which does not lie very close to the plates. 

 Its total concentration is determined accurately by Faraday's Law and 

 its resistance is a function only of this concentration and of the tem- 

 perature. B is the most active, variable, and interesting part of the 

 cell. It includes the active material, that part of the electrolyte which 

 is in the pores of this material, and that part of the electrolyte which is 



Figure 1. Section through storage cell. 



near the plates. For ordinary rates large concentration changes can be 

 assumed to extend not more than a millimeter or two from the outside 

 surface of the active material before they are equalized by mixture 

 with the main body of the electrolyte. 



When the cell is at rest, its resistance may be considered as being 

 made up of three parts. A, metallic in nature, and therefore with a 

 negative temperature coefficient, but constant at a fixed temperature. 



B, also metallic in its nature, and sufficiently low so that the resistance 

 of the electrolyte in its pores can be neglected in comparison with it. 



C, a purely electrolytic resistance, with positive temperature coefficient, 

 but constant at a fixed temperature. 



When the cell is working at a constant rate and fixed temperature, 

 A remains constant. C is a function only of the total concentration of 

 acid in the cell, and can be made constant by using small plates and a 

 large body of electrolyte. The resistance of 5 now becomes more com- 

 plex, and may be considered to break up into two parts, one a function 

 of the condition of the active material and the other a function of the 



