1908-9.] Electromotive Force of Iodine Concentration Cells. 311 
to yield erroneous results as the solutions get stronger, yet it seemed of 
some interest to measure the E.M.F. of a cell containing thrice normal KI., 
as this solution dissolves a number of molecules of iodine equal to the 
number of molecules of potassium iodide, so that it might be regarded as 
containing KL only. The results were as follows : — 
EMF= T01 ; NH 4 K0 3 correction = *02 ; number of iodine ions= '23. 
Total uncombined KI = ’275. 
It will be noted that while the total uncombined KI has not diminished 
much, it now represents a very small percentage of the total KI present, 
so that even this solution contains very little polyiodide higher than KI 3 . 
The amount, however, is now quite perceptible, and doubtless from this 
point onwards rapidly increases. 
It seemed also of interest to investigate the number of iodine ions present 
in a series of solutions consisting of normal KI, with successive additions 
of iodine up to saturation-point. Jakowkin has shown that in such solu- 
tions the value of k is ‘001365 where little iodine is present, but pro- 
gressively diminishes with addition of more iodine. In my former paper I 
determined the E.M.F. of a series of cells containing *0139 molecules of 
