1907-8.] Electromotive Force of Iodine Concentration Cells. 391 
KI. 
Iodine. 
E.M.F. 
•075 
•001 to -0001 
•0296 
•05 
•001 to *0001 
•0301 
•025 
•001 to -0001 
•0306 
•075 
•01 to -001 
•0358 
•05 
•01 to -001 
•0389 
•025 
•01 to *001 
•0501 
The close resemblance of this series to that obtained for water is obvious, 
the E.M.F., however, rising rather higher as the ratio of iodine is increased. 
If we assume that the E.M.F. obtained for -001 to '0001 iodine with 
*075 KI present is entirely due to the iodine concentrations, as we found to 
be very nearly true in the case of the water solutions, then the calculated 
value at 25° C. is '0295. These experiments prove, then, how accurately the 
Nernst equation applies to iodine solutions in alcohol, and also indicate the 
existence of KI S in the solutions. 
A series of solutions was made up containing different percentages of 
alcohol and water, but containing iodine and potassium iodide in the same 
ratios as measured above, and the following values were obtained, which 
were taken at the two temperatures, 25° C. and 0° C.: — 
Number op Molecules op Potassium Iodide = *025 in 1000 c.c. and Number op 
Iodine Molecules *01 against -001 in 1000 c.c. 
Percentage 
of Alcohol. 
Percentage 
of Water. 
E.M.F. at 25° C. 
E.M.F. at 0° C. 
Difference in 
E.M.F. 
100 
0 
•0505 
•0463 
•0042 
90 
10 
•0485 
•0442 
•0043 
80 
20 
•0476 
•0435 
•0042 
70 
30 
•0457 
•0419 
•0048 
60 
40 
•0454 
•0405 
*0049 
50 
50 
•0447 
•0398 
•0049 
40 
60 
•0445 
•0395 
•0050 
30 
70 
•0439 
•0388 
•0051 
20 
80 
•0435 
•0392 
•0043 
10 
90 
•0434 
•0393 
•0041 
0 
100 
•0428 
•0392 
•0036 
In the first place, if the E.M.F. of the alcohol cell is calculated for 0° C. 
from the value for 25° C., on the assumption that the E.M.F. is proportional 
to the absolute temperature, the calculated value is '0462, while the value 
obtained is '0463. In the second place, it will be noted on comparing the 
differences that they tend to increase for mixtures of alcohol and water, and 
diminish again for either pure alcohol or pure water. This result would 
