PAPERS OX CHEMISTRY AND PHYSICS 285 



other, the action of light would be merely to maintain 

 the equilibriimi by the formation of pentathionic acid 

 and colloidal sulfur as the reaction between H.S and the 

 acid proceeds. 



With certain assumptions reg'arding the mechanism 

 of the above process the explanation offered by Freund- 

 lich and Xathansohn can be reconciled with the fact 

 that the conductivity of the sol increases upon exposure 

 to light. If the process resulted in the reaction between 

 the first traces of pentathionic acid formed and H2S, 

 the conductivity of the sol could not increase, since no 

 substance of stifficiently high conductivity is formed to 

 account for the changes produced. On the other hand, 

 if the formation of S-hydrosol, whether by the photo- 

 chemical oxidation of H2S or by the HoS-pentathionic 

 acid reaction, is assimied, a gradual increase in con- 

 ductivity can be more readily explained. Colloidal sul- 

 fur produced by either or both of these reactions will 

 adsorb pentathionic acid as stabilizing electrolyte, the 

 S-micelles, with their adsorbed acid, serving to augment 

 the conductivity of the solution, and maintaining at the 

 same time a certain concentration of free acid in the in- 

 termicellular liquid by virtue of the adsorption equili- 

 brium set up. Both of these factors serve to increase 

 the conductance. Eventually the concentration of the 

 intermicellular pentathionic acid will reach such a value 

 that the rather slow reaction of the acid with intermicel- 

 lular HoS, which has been increasing in speed with con- 

 tinued increase in the concentration of the acid, will 

 proceed unhampered, an equilibrium having thus been 

 set up between the various components of the system. 

 The attainment of this equilibrium marks the end of 

 the increase in the conductivity of the sol. 



The fact that the rate of change of conductance in- 

 creases with decrease in the concentration of the sol is 

 readily explained in view of the work of several investi- 

 gators who have pointed out that dilution of a sol results 

 in increased dispersion, i. e., diminution of the size of 

 the particles. Increased dispersion of the colloid parti- 

 cles will favor the speed of the reaction due to the in- 

 creased photochemical activity of the micelles per unit 



