THE INTERNAL RESISTANCE OF THE LEAD 

 ACCUMULATOR. 



By Harry W. Morse and Ledyard W. Sargent. 



Presented by John Trowbridge, December 14, 1910. Received January 3, 1911. 



General Discussion. 



1. The internal resistance of a lead accumulator is not a factor of 

 importance in the practical operation of storage batteries. In a small 

 pocket battery it is only a few hundredths of an ohm : in medium sized 

 cells it sinks to a few thousandths, and in large cells, such as are used 

 in regulation and central station work, it is of the order of a few 

 hundred- thousandths of an ohm. In almost every case the cell re- 

 sistance is so low in comparison with the other resistances in the 

 working circuit that it can be neglected as far as practical calculation 

 is concerned. 



But the resistance of a cell and the changes which take place in this 

 factor are of much interest when the behavior of the cell is being 

 studied from a more general point of view. A lead accumulator seems 

 a very simple system indeed at first glance, but it is in fact a very 

 complex one, concealing many problems difficult of solution. While 

 the cell is at rest, fully charged, and therefore containing plates which 

 are good conductors from their center out to the boundary of the elec- 

 trolyte, its resistance is very nearly that of the acid between these 

 plates, and it can be calculated with fair approximation. But when 

 the cell is working, either on charge or discharge, its condition is most 

 variable. The acid must diffuse through a series of fine channels, and 

 great differences of acid concentration in the different layers of the 

 plates will be set up. Then, too, the particles of lead and lead per- 

 oxide, themselves good conductors, will be more or less completely 

 coated with lead sulphate — a bad conductor. The acid concentration 

 will, moreover, be a function of the rate at which the cell is working, 

 and the thickness of the lead sulphate coating over a particle of lead 

 or lead peroxide at any given point in the plate will also be a function 

 of the rate. 



2. An ideal section of a storage battery of two plates is shown in 



