1907-8.] Electromotive Force of Iodine Concentration Cells. 389 
that if no change on warming takes place in the distribution, according 
to the mass equation, the E.M.F. can be calculated from the formula 
E = 
•000198 
2 
T log 
; but if KI S is dissociated there will be a con- 
siderable change of E.M.F., the dissociation in the *0005 solution merely 
increasing the free iodine, but in the *05 per cent, solution both increasing 
the free iodine and the amount of KI, the E.M.F. tending to fall, therefore, 
to the value depending on the iodine concentrations alone. 
Table of E.M.F.s for Various Percentages of Iodine in Normal 
Potassium Iodide Solution. 
(a) 
Percentage of 
Iodine used by 
Jakowkin in mole- 
cules per litre. 
(b) 
Corresponding 
Values of K. 
(0 
Percentage used 
for E.M.F. in 
molecules per 
litre. 
(d) 
E.M.F. calculated 
from (6) and (c). 
(«) 
E.M.F. 
measured. 
•5066 
•000773 
•508 
•0636 
•0588 
•3615 
•000949 
•302 
•0527 
•0491 
•2784 
•001031 
•279 
•0461 
•0434 
•2088 
•001105 
•209 
•0398 
•0376 
T097 
•001220 
T09 
•0284 
•0273 
•0563 
•001292 
•056 
•0185 
•0184 
•0321 
•001315 
•0322 
•0108 
•0108 
•0141 
•001365 
•0139 
Such a cell, when raised to the temperature 75° C., gave the 
value E = ‘0848, while the calculated E.M.F., on the assumption that no 
change took place in the iodine distribution in the cell, gave the value 
E = *0880 ; so there is no indication of any serious change in the 2 
distribution up to this temperature. 
Electromotive Force of Iodine Concentration Cells in Alcohol. 
The evidence obtained from the absorption spectra of solutions of 
iodine in potassium iodide and alcohol points to the conclusion that KI 3 
is formed in the solutions, but the value of the constant for the mass 
equation is not known. 
We might venture to calculate this constant from the E.M.F. results if 
we knew accurately another figure, namely, the relative amounts of dis- 
