PROCEEDINGS OF THE AMERICAN ACADEMY. 



605 



for a given current and at constant temperature were accurately 



known. 



The other criterion of the condition of the cell now in use is the 

 plate potential. In order that this may give useful information it is 

 necessary to have a discharge curve, on which are plotted the cell vol- 

 tages at various times of discharge at constant current and constant 

 temperature. Once in possession of such a curve, measurement of 



Jf 



60 WO 



TIME-MINUTES 



160 



Figure 8. Curves showing resistance of paste plate cell during discharge at 

 various temperatures. 



cell voltage, at a known time after discharge at constant rate has begun, 

 gives accurate information as to the condition of the cell. 



It is evident that a measurement of the cell resistance serves equally 

 well to determine the condition of the cell, for the resistance-time 

 curves of Figure 5 are equally as characteristic as the voltage-time 

 curves of Figure 6. The greater difficulty of measurement of cell re- 

 sistance will probably prevent any practical application of this fact. 



Reversal of a Plants Cell. 

 10. It was considered a matter of interest to follow a cell at one 

 temperature through complete discharge and then on to more or less 

 complete reversal. If the explanation given on page 591 is correct, it 



