IOWA ACADEMY OF SCIENCES. 
197 
per cent solution of caustic soda or potash. Into the caus- 
tic soda is immersed the usual zinc electrode, suspended 
from the cover of the container. 
The following comparative tests were made with the 
Edison, Gordon and the above described tin can cell. 
The cells were placed successively in a closed circuit for 
a period of twenty-four hours. The external resistance of 
the circuit was .8 ohm. At stated intervals the internal 
resistance and E. M. F. of each cell were determined. The 
condenser method described on page 100, paragraph 55 of 
Carhart and Patterson Electrical Measurements was em- 
ployed in these determinations. The apparatus used was 
a Rowland D’Arsonval galvanometer, a one-half micro- 
farad condenser, a charge and discharge key, a resistance 
box and a standard Carhart-Clark cell. A diagram show- 
ing the connections of the apparatus will be found in Car- 
hart and Patterson’s work. 
The E. M. F. of the Edison cell on closed circuit was .76 
volts at the beginning. At the end of ten hours it reached 
.67 volts which it maintained during the entire run. It 
showed an initial internal resistance of .15 ohm which was 
reduced to its rated resistance of .05 ohm at the end of six 
hours at which it remained. The cell delivered a perfectly 
constant current of .8 ampere during the entire time. 
There were no observable changes in its E. M. F., resistance 
or current during the second twenty-four hours of its flow. 
The E. M. F. of the Gordon cell sank at once to .7 volt at 
the beginning of the run and gradually lowered to .67 in 
three or four hours which it finally maintained. Its internal 
resistance at the beginning was .25 ohm which was gradu- 
ally reduced to .08 ohm where it remained. The current 
was practically constant after the first four hours with a 
strength of .77 ampere. 
The sheet steel cell started with an initial E. M. F. of .88 
volts. It reached .76 volt at the end of four hours where 
it remained during the time of the test. Its initial internal 
resistance was .1 ohm which was reduced in a few hours to 
.05 ohm. After the first four hours the current reached .9 
