380 Proceedings of the Royal Society of Edinburgh. [Sess. 
KI and an excess of solid iodine. Round the other electrode was placed a 
series of solutions of iodine in alcohol containing ’025 KI. 
The following table contains the approximate strengths of these iodine 
solutions and E.M.F.s of the cells at 25° C. and 14° C. : — 
Current in the direction of transferring KI from alcohol to water 
defined as -f-ve: — 
Table I. 
Water. 
Alcohol. 
O 
^ CM 
1 
E.M.F. 
at 14° C. 
•025 KI + -0138 I 2 
•025 KI 
•043 I 2 
•069 + 
•033 + 
•025 KI + -0138 I 2 
025 KI 
•086 I 2 
•009 + 
•014- 
•025 KI + -0138 I 2 
•025 KI 
T72 I 2 
•028- 
•070- 
•025 KI + -0138 I 2 
•025 KI 
•345 I 2 
071- 
•099- 
Result obtained before — 
■025 KI + -001 I 2 
•025 KI 001 1 2 
•198 + 
T.C. -00037 + ve. 
If the table of E.M.F.s at 25° C. is examined, it will be noticed in the 
first place that as the iodine in alcohol is increased in strength the E.M.F. 
is finally reversed, the current flowing the other way, and the neutral point 
of zero E.M.F. being somewhere about a concentration of - 086 molecules 
of I 2 . 
This is all in accord with the theory of such cells as developed by 
Luther and Abel. If now the column of E.M.F.s at 14° C. is examined, it 
will be noted that while the current was in the direction necessary to 
transfer potassium iodide from alcohol to water (which for convenience 
in this paper will be defined as the positive direction) the temperature 
coefficient was positive, but when the current was reversed so as to convey 
potassium iodide from water to alcohol the temperature coefficient became 
negative and the cell therefore exothermic, the cell doing work and also 
setting free heat. 
The result given at the beginning of the paper, although the concen- 
tration dealt with was different, evidently harmonises with and fits into 
this table. 
