of Edinburgh, Session 1884 - 85 . 
335 
little higher for distilled water, and not falling quite so low for 
saturated iodide of zinc. 
On comparing these numbers with those already mentioned as 
given by Naumann, we find that the number (expressed in volts) 
which he gives for the heat of combination of zinc and iodine is 
1 '085 volts. The electromotive force of an iodine cell with about 
*04 grm. of free iodine, in saturated iodide of zinc solution, is 1 '082 
volts. Naumann gives the heat of solution of zinc iodide in water 
as *162 volts. The average number obtained from the curve is 
"110 volts. The number given by Naumann is higher, because it 
does not represent the average heat of solution up to a saturated 
solution of zinc iodide. 
In conclusion, I think these experiments are sufficient to show 
that we have here a method peculiarly suitable for the determination 
of the heat of solution of salts, as it is possible to study the 
behaviour of the salt under any required constant conditions. 
Tor instance, the heat of solution of zinc iodide in water contain- 
ing other salts in solution could be evidently determined with great 
accuracy by this method. It seems probable that another advan 
tage of the method is that no heat requires to be absorbed in vary 
ing the salt from a solid to a liquid state. I have not found any 
indication that the heat required for this change, in the case of zinc 
iodide, is at all considerable. 
Table (a).- — Variations in Electromotive Force caused by varying the 
Zinc Iodide in solution as measured in the Zinc-Cuprous Iodide 
Cell 
Electromotive Force in Volts. 
Grms. of Znl 2 in 1 grm. of Water. 
•390 
3-870 
•419 
3-640 
•451 
2-490 
•488 
1-860 
•545 
•537 
•607 
•236 
•637 
•118 
•656 
•059 
•696 
=029 
•771 
j -003 
•894 
D.W, 
