832 Proceedings of the Royal Society 
already mentioned, the E.M.F. of zinc in the ordinary iodine cell 
is about 60. 
The difference 3 is due to an E.M.F set up between the iodine 
solution and the iodide of zinc solution. 
The deflection with copper is 33. 
Some experiments were then made with a cuprous iodide cell 
constructed in the manner already described. The following table 
contains the results : — 
Name of Metal. 
E.M.F. in 
Iodine Cell. 
Calculated 
E.M.F. 
in Cuprous 
Iodide Cell. 
Found E.M.F. 
in Cuprous 
Iodide Cell. 
Zinc, .... 
60-5 
30 
32 
Copper, .... 
30-5 
0 
0 
Silver, .... 
29 
-1-5 
0 
Lead, .... 
39 
8-5 
10 
Tin, .... 
29 
... 
... 
Iron, .... 
31 
'5 
0 
The second column of figures is found on the assumption that 
the E.M.F. of a metal in the cuprous iodide cell is its E.M.F. in the 
iodine cell, minus the E.M.F. of copper in the iodine cell. 
Three has been subtracted from the numbers in the first column. 
The reason for doing this has been already explained. Taking 
61*5 as the E.M.F. of zinc, which is the mean value, its heat of 
combination with iodine as calculated from the above formula 
is 924. 
The number given by Naumann for the heat of combination of 
zinc with iodine in presence of water is 929. 
Nearly all our other numbers agree approximately with those 
given in Naumann’s Thermochemie . 
The numbers, taken from Naumann’s table, are the heats of com- 
bination of one gramme of the metals in presence of water. It will 
be seen that the value given for iron by Naumann does not show 
any agreement with our value. This is also the case with the 
chlorine and bromine compounds of iron. 
