488 Dr. C. H. Draper on the 



force of a Daniell cell as 1*1 volt), using 



2 Grove cells, polarization E.M.F. =2*15 volts. 



4 V ?> v -=l'o ,, 



" jj » ■>■> =2'0 „ 



The objects with which the experiments described below 

 were undertaken were to ascertain whether the electromotive 

 force of polarization has a sensibly constant value beyond a 

 certain maximum limit, and what is the effect upon it 

 of change of temperature. The method of experimenting- 

 was to pass currents of various known strengths through a 

 voltameter filled with dilute sulphuric acid, and to note 

 the difference of potential between the electrodes by means 

 of a quadrant-electrometer. Since Ohm's law is true for 

 electrolytes, at least within the limits of probable error 

 in experiments of this kind, there will be a difference of 

 potential between the electrodes just as between the two 

 ends of a wire. If R be the resistance of the column of 

 liquid, and C a value of the current which is not less than 

 that value corresponding to e the maximum value of the 

 electromotive force of polarization, and if E be the dif- 

 ference of potential observed between the electrodes, then 

 E = ?+CR. Any increase in the value of C will now be 

 the accompaniment of an increase in the value of E. If, 

 then, the observed values of E and C be marked out along 

 axes at right angles to each other, 

 the equation E = e 4- CR will re- Fig. 1. 



present a straight line, e being 

 represented by the intercept on 

 the axis of potential (Oy), and the 

 resistance of the voltameter being 

 indicated by the tangent of the 

 angle which the straight line makes 

 with the axis of the current (0«i*). 

 If, then, the temperature at which 

 the process takes place has an effect 

 on the amount of the maximum po- ° 

 larization, this will be manifested by 



a change in the value of the intercept, while the change in 

 the slope of the line will indicate the change in the resistance 

 of the voltameter. 



Apparatus. — The circuit consisted of a battery, B, and a 

 voltameter, V, connected through a commutating-key, K, 

 with a tangent-galvanometer, G, the electrodes of the volta- 

 meter being connected also with the terminals of a quadrant- 

 electrometer, E. The voltameter was placed inside a large 



