1908-9.] Electromotive Force of Iodine Concentration Cells. 307 
poured into the bottle in which the stoppered electrodes were to be 
immersed. 
The other electrode was then filled up with coarsely powdered iodine, 
and some more of the same solution was run in among the powdered iodine 
by means of a fine pipette till the electrode was full. It was then stoppered, 
and finally immersed in the bottle along with the other electrode. The 
whole cell was then sealed with paraffin-wax and placed in the thermostat. 
The electromotive force usually rose rapidly, reaching its maximum in 
E.M.Fs. of saturated solution. 
•12 
Graph 1. 
about twenty-four hours and then remaining constant for some days. 
Readings taken after a week showed usually a slow dropping of E.M.F., 
probably due to the gradual diffusion of the iodine from the strong electrode, 
through the solution and into the weak electrode. 
The iodine and potassium iodide used were Merks’s pure preparations. 
As a check, a preparation of specially pure iodine was made by dissolving 
Merks’s pure iodine in strong potassium iodide, precipitating by dilution 
with water, washing, drying over calcium nitrate, and finally subliming. 
This iodine introduced into the electrode instead of the iodine formerly 
used did not cause any appreciable change in the E.M.F. 
Although all the values given are not the result of more than one measure- 
