314 
He has shown that the second reaction has a temperature coefficient 
less than unity (about 0.83) in presence of sodium sulphate and 
sodium bisulphate (Zeit. Elektrochem. 1915, 21, 461). 
As these results are rather peculiar, it was thought worth while 
to re-investigate some of these cases. 
A dilute solution of iodie acid was prepared and potassium iodide 
added to this solution. The reaction is very rapid and it is practically 
impossible to determine its temperature coefficient; when the two 
sotutions are mixed at O°, iodine immediately separates. The mixture 
is divided into two parts, one of the two tubes is put into ice and 
the other heated to boiling. Now the hot tube is cooled and brought 
to the same temperature as the other and the colour of the two 
tubes compared. Generally it is very difficult to find any difference 
“in the two tubes. Sometimes the heated seems more pale probably 
due to the volatilisation of iodine when the tube is heated. Conse- 
quently the temperature coefficient without any sulphate is practically 
unity. 
Similar experiments were made in presence of concentrated solu- 
tions of sodium sulphate and magnesium sulphate. In presence of 
these sulphates, a mixture of iodie acid and potassium iodide liberates 
slightly less iodine at a high temperature than at ordinary temperat- 
ures, hence a slight negative effect, of increase of temperature on 
the velocity of the reaction between iodic acid and potassium iodide, 
is observed. 
On the other hand, potassium sulphate, potash alum, manganese 
sulphate etc. are quite ineffective in changing the temperature coef- 
ficient of the reaction between iodie acid and potassium iodide. The 
behaviour of potassium sulphate is different from that of sodium 
sulphate, since a saturated solution of sodium sulphate is richer in 
SO," ions than a saturated solution of potassium sulphate at the 
same temperature. The temperature coefficient of the reaction between 
iodie acid and potassium iodide in presence of the above sulphates 
is practically unity. 
Ammonium and zine sulphates behave differently and in their 
presence the temperature coefficient becomes greater than unity. 
Marked difference is noticeable in the two tubes; the tube, which 
is heated, contains much more free iodine than the tube kept at O°. 
The explanation of this behaviour is connected with the phenom- 
enon of hydrolysis. The sulphates of sodium, magnesium etc. are 
very slightly alkaline, since the basic portions in these salts are 
stronger than the acid portion. At higher temperatures more OH’- 
ions are produced, since temperature greatly increases the amount 
