olr2 Dr. C. R. A. Wright on the Determination of 



Second Cell. 



Current, in 

 micro webers. 



Microwebers 

 per square 

 centimetre. 



E, in volts. 



CE. 



_e=-(E-CK). 











-1-105 





1-105 



11-2 



11 



-1105 





1-105 



36-8 



37 



-1-094 



•001 



1-095 



109-1 



109 



-1-082 



•004 



1-086 



265-5 



266 



-1-053 



•010 



1-063 



515"5 



516 



-1020 



•021 



1041 



1140-0 



1140 



-0-982 



•046 



1-028 



In these experiments the correction CR is only approxi- 

 mate, it being impossible to calculate the precise value of R 

 with any great degree of accuracy ; but evidently, except in 

 the last one or two determinations, even a large error in the 

 value of R would make no appreciable difference in the end 

 result, viz. that the E.M.F. of a Daniell cell regularly decreases 

 as the current 'produced increases, but not at so rapid a rate. 



During the time that these observations were being made, 

 the changes in the E.M.F. of. the cell due to "running 

 clown" and variation of the.' density of the solutions sur- 

 rounding the two plates respectively, were too small to be 

 capable of measurement. After making an observation with 

 a larger current and reducing the current to a smaller value 

 or to nil, sensibly the same value was always obtained whether 

 at the beginning or end of the series of measurements, which 

 lasted some two or three hours in each case. If, however, 

 observations were made one day and then repeated a day or 

 two after, concordance was rarely noticeable between the 

 results : the later experiments always showed a more rapid 

 rate of fall in the numerical value of — e with the current- 

 increase than the earlier ones, and also generally indicated a 

 perceptibly lower value when the current was nil. Apparently 

 this result was due to the deposition of copper on the surface 

 of the zinc plate, owing to diffusion. 



Experiments are now in progress in which the true value 

 of R for any given cell is determined by a new method : so 

 far these have given results entirely confirming those above 

 described. The highest values hitherto obtained for the E.M.F. 

 of a freshly arranged DanielPs cell generating an indefinitely 

 minute current only, and freed from complicating circum- 

 stances as far as possible (especially presence of dissolved air, 

 which tends slightly to lower the value), are between 1*105 

 and 1*110 volt (Clark's cell being 1*457 volt) at the tempera- 

 ture of 15° or thereabouts. The discussion of these experi- 



