308 Proceedings of the Royal Society of Edinburgh. [Sess. 
ment, the more important values were determined more than once with freshly 
prepared solutions, and found to agree very closely (in dilute solutions, usually 
within ‘0003 of a volt). The intermediate values when plotted give a perfectly 
smooth curve, graph 1. In strong solutions the saturation-point cannot be 
determined quite so sharply, but an error of a millivolt is the outside limit. 
The following table contains (1) the number of molecules of potassium 
iodide present, (2) the number of molecules of iodine present in the dilute 
iodine electrode, (3) the E.M.F. with potassium iodide of the same strength 
connecting the stoppered electrodes, (4) the correction in E.M.F. obtained by 
immersing the stoppered electrodes in ammonium nitrate, (5) the number 
of iodine ions present calculated from the corrected E.M.F., and (6) the 
total amount of uncombined KI present. 
All the ammonium nitrate corrections given were experimentally deter- 
mined except the one for *7 KI, which was obtained by interpolation. 
Table T. — E.M.F. for Saturated Iodine against ’0005 Iodine Molecules. 
No. of KI 
Molecules. 
No. of Iodine 
Molecules. 
E.M.F. 
NH 4 N0 3 
Correction. 
No. of 
Iodine Ions. 
Total 
Free KI. 
•025 
•0005 
•0640 
+ -0030 
•0117 
•0127 
•05 
•0005 
•0728 
+ -0034 
•0226 
•025 
T15 
•0005 
•0830 
+ -0039 
•05 
•056 
•344 
•0005 
•0987 
-b "0044 
T35 
T57 
•5 
•0005 
T040 
+ -0046 
T84 
•22 
•7 
•0005 
•1099 
+ -0055 
•23 
•273 
•85 
•0005 
T136 
+ -0064 
•256 
•307 
1-0 
•0005 
T172 
+ -0008 
•264 
•317* 
* This does not agree with the value calculated by Maitland (Z. /. Eletrocli., 1906, 
265), hut his calculation involves Crotogino’s E.M.F. for a normal KI sat. iodine cell, 
which probably requires a considerable correction for contact E.M.F. due to I 3 ions. 
In order to determine the amount of combined iodine present the 
amount was calculated for the dilute solutions by interpolation from the 
results of Noyes and Seidenstecker.* As the solutions used by me do not 
differ greatly from theirs in the amount of KI present, this can be done 
safely. At the same time independent determinations were made for these 
dilute solutions and found to agree so closely with the figures obtained by 
interpolation that they were taken. 
For solutions above T normal KI, fresh determinations of the satu- 
ration-points were made in the following manner. The potassium iodide 
solution with excess of solid iodine was introduced into a closely stoppered 
bottle sealed outside with paraffin-wax and placed in a thermostat at 25° C. 
After being kept rotating in the thermostat for more than a week, the 
* Zeits. Phys. Cliem ., xxvii. 357. 
