MORSE AND SARGENT. — RESISTANCE OF LEAD ACCUMULATOR. 593 



and the conducting material of the plate, and the result is a consider- 

 able increase in resistance. 



While it is true that the concentration and therefore the resistance 

 of the main body of the electrolyte is completely determined by 

 Faraday's Law, the passage of the same quantity of electricity may 

 result very differently in various types of cells. Change in concentra- 

 tion and resistance will be great in those types which have large 

 weight of plates in proportion to their content of electrolyte. They 

 will be small in the types where weight is not a factor to be considered 

 and where a large excess of acid is maintained. 



Other factors which may effect resistance will be discussed in con- 

 nection with the data of this paper. 



4. On page 611 will be found a list of references on the subject 

 of the resistance of galvanic cells and accumulators. Many of these 

 papers were written at a time when the difficulty of such measure- 

 ments was not understood, and it may be said that the research of 

 Nernst and Haagn (1896) was pioneer work, and that they showed for 

 the first time how to eliminate the disturbing factors of the problem. 

 The measurements of Dolazalek and Gahl (1901) are still more accu- 

 rate and include data on several types of cell and on various rates of 

 charge and discharge. 



Our attention has been turned largely toward the temperature 

 coefficients of resistance under various conditions, for we wished to 

 exhibit as clearly as possible the dynamic nature of the phenomena 

 in the lead accumulator. After investigation of the other methods of 

 measurement, we adopted the form of bridge described by Ayres [20]. 

 Ayres himself did not use the bridge for measurements on storage 

 cells, ndr indeed for any very low resistances of electrolytic nature. 

 But we have found this type of bridge, with slight alteration, to be 

 most satisfactory for the measurement of electrolytic resistances of the 

 order of 0.01 to 0.10 ohm. 



The Bridge and Auxiliary Apparatus. 



5. The bridge connections are shown in Figure 2, together with 

 the circuit used in charging and discharging the cell and the secondary 

 bridge on which resistances were measured after balance had been ob- 

 tained. The bridge itself is symmetric, and contains a meter slide 

 wire of manganin of about 0.40 ohm resistance. At opposite ends of 

 this wire connection is made to the source of alternating current and 

 to the two other arms of the bridge. The cell arm contains the cell 

 under investigation in series with a capacity Ci : the other arm con- 



VOL. XLVI. — 38 



