ELECTRO-CHEMICAL EQUIVALENT OP SILVER, 
453 
f rdt 
J t ’ 
viz., the mean value of r necessary for a balance of E.M.F. during the time that the 
current ran through the voltameters. To get this the actual observations of r are 
plotted, the times being taken as abscissse, and a curve constructed representing the 
value of r throughout the course of the experiment.* From this curve the ordinates 
are measured, which correspond to the middle of every five minutes’ period. The 
values of r thus obtained are 
Table XII. 
Time. 
r. 
Time. 
r. 
HI. 
m. 
21 
-22 
321 
+ 32 
7jt 
-16 
371 
+ 48 
m 
-10 
421- 
+ 66 
m 
— 2 
471 
+ 86 
221 
+ 8 
521 
+ 112 
271 
+ 18 
574 
+140 
Mean= + 38'3. 
The rapid falling-off of the current towards the end of the hour is believed to be 
due to the formation of crystals upon the anodes of the cells charged with silver 
chlorate. The value of 
being thus found to be 4960‘7, the calculation of E may be completed. Taking 
w— 1T1 80 X 10~ 2 , we get 
E= 1*4562 B.A. volts, 
as the electromotive force of No. 4 Clark at 13°T. 
On April 2 an equally satisfactory result was found from the silver deposits without 
use of the current weighings. It will be seen that in this way anyone may determine 
the E.M.F. of his standard battery with a very moderate expenditure of trouble and 
without the need of any special apparatus. So large a resistance in the main circuit 
as in the above example, due to the idle coils of the current-measuring apparatus, is 
not necessary, but some resistance in addition to R and that of the battery and 
voltameters would probably be advisable. Otherwise the magnitude of the current 
would be too sensitive to the resistance of the voltameters, which cannot be included 
* In the formation of the curve use was made of observations in which the galvanometer balance was 
incomplete, the valne of the scale divisions being approximately known. 
