1885.] 



On Charging Secondary Batteries. 



351 



Take No. 4, which is the diagram of this morning's (April 28) 

 charge of 15 cells. The following are the particulars : — 





E. 



C. 



D. 



9.0 A.M. 



S7-7 



32-24 



1115 



10.0 „ 



40-2 



32-24 



1119 



11.0 „ 



42-5 



31-50 



1121 



12.0 noon 



42-5 



30-74 



1123 



1.0 P.M. 



42-5 



29-95 



1124 



2.0 „ 



42-5 



29-95 



1124 



6. It is evident that after four hours' continuous charging the 

 battery was full, for the density, the electromotive force, and the 

 strength of current became constant. The same scale of ordinates 

 is used for volts and amperes. When each magnitude reaches its 

 constant bubbles of gas are freely given forth, and energy is being 

 wasted. The variation of the electromotive force and current strength 

 is clearly due to the counter-electromotive force of the cells, which 

 becomes a maximum only when the plates are fully formed. The 

 counter- electromotive force partakes of the character of a higher 

 resistance opposing the charging current, and increasing the propor- 

 tion of the current through the shunt of the dynamo. Hence the 

 changes of electromotive force are more marked than those of the 

 current. Indeed, the changes in the electromotive force, as given by 

 the voltmeter, are sufficient alone to indicate the progress and com- 

 pletion of the charge. They are more reliable than the evolution of 

 gas. My dynamo is a shunt- wound Gramme, my voltmeter is Cardew's, 



