1348 
Evidently it is clear tliat just as liydrogen ions catalytically 
accelerate the actioii of iodine on acetone, so light is also a positive 
catalysor in the above reaction. 
Priok (Zeit. Phys. Chem. 1898, 27 , 474) has shown that persul- 
phates slowly liberate iodine from iodides in aqueous solution accord- 
ing to the folio wing eqnation : 
4- 2 KI = 2 K,SO, + I,. 
According to the Chemical eqnation it should be one of the third 
order bnt investigation by the ordinary methods of Chemical dynamics 
showed it to be of the second order; evidently the reaction takes 
place in stages. Moreover, Price has shown that the reaction is 
seiisitive to the catalytic intluence of iron and copper salts, a marked 
acceleration being prodnced even in the presence of Solutions 
of either ferrous sulphate or copper sulphate. In each case the 
acceleration is directly proportional to the concentration of the 
catalyst and in the case of iron salts independent of whether it is 
added as ferrous or ferric salt. 
The action of light on this Chemical change has now been in- 
vestigated and it has been found out that light, as in other instances. 
Sodium persulphate and potassium iodide at 30° 
! 
Quality of light ' 
Time of , 
exposure 
i 
Amount of 
iodine 
liberated 
‘ Volume of solution 
1) Sunlight 
109' 
0.01054 
N 
1 5 c.c. persulphate and 
Darkness 
100' 
0.00926 
1 10 c.c. ^ KI and 50 c.c. 
distilled water 
2) Sunlight 
140' 
0.01475 
Do 
Darkness 
140' 
0.01355 
i 
3) Sunlight 
80' 
0.00732 
Do 
Darkness 
80' 
0.00638 
4) Diffused light 
70' 
0.00668 
Do 
Darkness 
70' 
0.00579 
i 
N 
1 10 c.c -Q persulphate and 
5) Diffused light 
120' 
0.01388 
Darkness 
120' 
0.01299 
1 10 c.c. ^ KI and 25 c.c. 
water 
6) Diffused light 
' 60' 
0.00694 
Do 
Darkness 
‘ 60' 
0.00635 
) 
