1121 
Evidently it is clear that just as hydrogen ions catalytically 
accelerate the action of iodine on acetone, so light is also a positive 
catalysor in the above reaction. 
Price. (Zeit. Phys. Chem. 1898, 27, 474) has shown that persul- 
phates slowly liberate iodine from iodides in aqueous solution accord- 
ing to the following equation : 
K,S,0, + 2 KI = 2 K,SO, + 
According to the chemical equation it should be one of the third 
order, but investigation by the ordinary methods of chemical dynamics 
showed it to be of the second order; evidently the reaction takes 
place in stages. Moreover, Prick has shown that the reaction is 
sensitive to the catalytic influence of iron and copper salts, a marked 
acceleration being produced even in the presence of Alen 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° 
EE LY TS ET 
. Amount of 
Quality of light Time of iodine Volume of solution 
exposure 
xP liberated 
[| D:c¢ af ersulphate and 
1) Sunlight 109 0.01054 | °°“ 10 P P 
p N 
Darkness 100’ 0.00926 | Onee: 5 KI and 50 c.c. 
| | distilled water 
2) Sunlight | 140 0.01475 | 
| | Do 
Darkness 140’ 0.01355 | 
3) Sunlight 80’ 0.00732 | 
| Do 
Darkness 80’ 0.00638 | 
4) Diffused light 70’ 0.00668 
Do 
Darkness 70’ 0.00579 | 
| N 
5) Diffused light] 120’ Ox01386 IAA Tore Oee 
| N 
Darkness | 120’ 0.01299 GG 5 Kl and 25 cc. 
| water 
6) Diffused light | 60’ 0.00694 | | 
| Do 
Darkness | 60’ 0.00635 
