495 
of hydroljsis, and these OH^-ions react on the iodine which is set 
free re-fornaing iodide and iodate. 
Hencö at the higher tempepatiires, less iodine seerne to be formed 
from the mixture of iodic acid and potassium iodide in presence of 
concentrated sodium or magnesium sulphate. 
On the other hand, Solutions of zinc and ammonium sulphates 
produce H’*ions due to hydroljsis and these H’-ions are very active 
in liberating iodine according to the foliowing equation : 
I O', 4- 5 r + 6 H- = 3 I, + 3 H,0. 
Moreover, I ha\ e repeatedly observed that addition of acids pro- 
duces more iodine, from a mixture of iodic acid and potassium 
iodide, than in the absence of acids. 
Hence the abnormal effect of teraperature on the velocity of the 
reaction bel ween iodic acid and potassium iodide in presence of 
sodium sulphate ascribed by Skrabal to complex formation, is really 
due to secondary changes produced by the interaction of theproducts 
of the hydrolysis on the reacting substances. 
A sirailar explanation is applicable to the small temperature coef- 
ficients obtained in the reaction between iodic acid and potassium 
iodide in presence of sodium acetate, sodium phosphate and potas- 
sium fluoride; because ali these salts are alkaline due to hydrolysis. 
The reaction between iodic acid and potassium iodide is extreraely 
rapid even at 0°. The reactions between KI and K^S^Og and KI 
and HgOj have smaller velocities than that between HIO, and KI. 
These two reactions have temperature coefficients greater than unity. 
Experiments were made on the effect of concentrated MgS 04 solution 
on the influence of temperature on the reactions between Hl and 
KjSjOg and Hl and HjO,. Even in presence of MgSO^, these two 
reactions have temperature coefficients greater than unity. The hot 
tubes contain much more iodine than the cold ones. 
In this connection, it is interesting to observe that the solubility 
of iodine in KI or Hl is greatly diminished by the presence of MgSO^. 
HCl does not produce an increase in the amount of iodine libe- 
rated in the foliowing cases : 
(a) KjSjOg -{- KI, (ó) KjSjOg -f- Hl, (c) Ferric nitrate -j- KI. 
In the foliowing cases, HCl markedly increases the amount of iodine. 
(a) H,0, + KI, (d) H,0, + Hl, (c) HlOg + KI, (d) HIO, + Hl, 
(e) H.Cr^O, + Hl, (/) K^Fe (CN), -f KI, (^) HNO, + KI. 
The last two reactions have temperature coefficients greater than 
unity even in presence of HCl. 
