805 
of Edinburgh , Session 1881-82. 
chloride cell and to the iodine cell recently described to the Society, 
on account of the simplicity of the reactions in both these cells, 
and that it could in this way be used as a simple method for the 
determination of the heats of combination of the metals with the 
halogens, by determining their electromotive forces, as the active 
elements in one or other of these cells. Mr. Burton and I accord- 
ingly set to work to investigate the matter. 
In our first experiments we used an iodine cell and a cuprous 
iodide cell, the cuprous iodide being used in place of cuprous 
chloride. 
The EMF of a cuprous iodide cell depends on the heat of com- 
bination of zinc with iodine minus the heat of combination of 
copper with iodine. The heat of combination of copper with iodine 
may be found by using copper as the positive metal in the iodine 
cell. Or we may determine the heat of combination of zinc with 
iodine directly in the iodine cell. The cuprous iodide cell, how- 
ever, offers some advantages. The heat of combination of almost 
any metal with iodine can thus be measured. 
The same method is aj:>plicable to chlorine and bromine com- 
pounds. The results obtained so far have been very satisfactory. 
Our numbers usually differ a little from the numbers found in 
calorimeter experiments. This discrepancy is to be expected, as the 
circumstances under which the combinations take place are so 
different in the two cases, and as we have not yet attempted any 
corrections. 
The simplicity and rapidity of the method are sufficiently obvious, 
and it is particularly applicable to cases where only very small 
quantities of a metal can be obtained, and where the metal, when 
obtained, is too rare to be wasted in the calorimeter. 
We hope to communicate to the Society the account of our ex- 
periments at a future meeting. 
