628 



is furnished by the shape of the curve found for the current potential 

 with AICI3 sohitions. This line is absolutely connected with the 

 so-called Irregular series. 



From what is stated in § 3 in connection with Table IV (lig. 3, 

 respectively) of the preceding paper it follows that the concentration 

 at which the battery shows an exchange of poles, is also that of 

 the zero-charge of the capillary, whilst its positive charge goes up 

 to about 3,u mol. and thence lowers without however i-eacliing zero 

 again. An AlCl^ solution will consequently have first a discharging 

 and therefore a coagulating effect on a negative sol. ; at higher concen- 

 trations it will render it a positive sol and onlj- at a much higher 

 concentration it will again reverse the charge and cause coagulation. 

 But therewith are described exactly the phenomena which, for instance, 

 have been observed by Buxton and Targue'), when they coagulated 

 mastix with AICI3 and indigo or Pt with FeCl^. The lower non- 

 coalescent, the lower coalescent zone, the upper non- and coalescent 

 zones, they can so to say be read off from the figures of the preceding 

 communication. 



One is accustomed to attribute the phenomenon of the irregular 

 series to a special action of tiie hydrolytically resolved hydroxides 

 of the coagulating ion. In coiuieclion with the preceding arises a doubt 

 whether to A1(0H)3 ought really to be atti-ibuted a preponderating 

 significance. For it does not seem probable that the AICI3 which is 

 present in such a small concentration, can cause a reversal of charge 

 in the capillary. Much more acceptable seems the following idea. A 

 strongly discharging cation unloads the capillary at such a small 

 concentration that the small anion-concentration cannot prevent a 

 complete reversal of charge. Of this the anion-concentrations are 

 capable in the case of Ba-- and K- because there the charge gets 

 nearer the zero value only at so much lai-ger concenti-ations. 



Hence, the afterzone phenomenon will occur, as soon as the dis- 

 charge by the cation is already very large at small concentrations 

 and is favoured by a feeble action of the anions. This strongly dis- 

 charging action of the cation may arise froui its higher valency or 

 from its strong adsorbability. The fact that irregular series w^ere 

 observed, for instance, also with strychnine nitrate, new fuchsin, 

 brilliant-green, auramine and silver nitrate '^) is quite in harmony 

 with this argument. For here we are dealing with strongly adsorb- 

 able cations and because they are univalent the equivalent anion 



1) Z. f. physik. Gbem. 57, 64 (1907, 

 -) Fheundlich, 1. c. 



