FLOCCULATION 



49 



of opposite charge from that borne by the colloidal particle. Thus the AsoSs 

 sol may be flocculated by cations such as Na+, Ca+ + , or A1+ + +, while the 

 Fe(OH)3 sol may be flocculated by anions such as Cl~, NOs", or SO4 . 



T.-VBLE II FLOCCULATING EFFECT OF ELECTROLYTES ON HYDROPHOBIC SOLS (dAVA OF 



FREUNDLICH, I9O3.) THE CONCENTRATION OF ELECTROLYTES IS THE MINIMUM WHICH 

 RESULTS IN COMPLETE FLOCCULATION 



Furthermore, the flocculating effect increases with an increase in the 

 valency of the effective ion. The first part of Table 1 1 shows that the 

 trivalent cation A1 + + + is more effective in flocculating the negatively charged' 

 AS2S3 sol than the bivalent cations Ca++, Ba++ or Alg+ + , which in turn 

 are much more effective than the univalent cations K+, Na+, and Li + . 

 Similarly the second part of the table shows that the flocculating effect of 

 bivalent anions (SO4 , CroOy ) upon a positively charged Fe(OH)3 

 sol is greater than that of univalent anions (Cl~, NOs^). 



However, the influence of the valency of an ion upon its flocculating 

 effectiveness does not follow a simple 1:2:3 arithmetical ratio. It took, 

 as shown in Table 11, about 88 times as much NaCl as CaCU, and about 

 7 times as much CaCU as AICI3 to accomplish complete flocculation of the 

 AS2S3 sol. 



In the flocculation of hydrophobic sols the ion of the added electrolyte 

 with a charge of the same sign as that of the micelle is not entirely without 

 effect. The influence of such ions is usually to increase the stability of the 

 system. Precisely stated, therefore, the influence of an electrolyte upon the 



