Precipitation oj Colloids. 



581 



The next series of: concentration values were taken from 

 some data by Freundlich, corrected For dissociation, so that, 

 as before, the minimal concentration or" cations per litre is 

 shown required to precipitate colloidal As 2 S 8 , at a concen- 

 tration of '007539 mols. per litre. The anion in every case 

 is 01'. The colloid is negatively charged. 



Table II. 



Cation. 



Minima] 

 concentration. 



H' 



Lf 



Na" 



029 

 0513 



•045 



Mg" 



•000717 



Af- 



■000093 



K' 



•044 



Ca*" 



•00065 



Zn" 



•0006S5 



Sr" 



•000635 



Ba" 



•00069 







Log 10 . 

 Minimal 



concent rat ion. 



Atomic 

 number. 



Atomic 

 number. 



2- -1 62 

 2-710 

 2-058 

 4-855 



2048 

 4 -SI 3 

 4836 

 4-803 



4-889 



1 

 3 

 11 

 12 

 13 

 19 

 20 

 .•so 



38 

 56 







•477 

 1-041 

 1079 

 1114 

 1-279 

 1-301 

 1-477 

 1-580 

 1-748 



Here again we find the univalent ions lie approximately 

 upon a straight line, to which the equation is 



(,\ = 0-55N-°-° 9 . 



The number of values for divalent ions is larger in this case 

 but they do not give a very concordant result. We can, 

 however, draw a line parallel to the first passing through 

 the plotted results, to which the equation is 



Co = -0008184 N -0 ' 09 . 



It is to be expected that secondary effects in dissociation 

 will be more evident the higher the valence of the cation. 



The question now arises as to the way in which we are to 

 reconcile these results, if real, with Whethanrs law. This 

 states that the minimal concentrations of any univalent, 

 divalent, and trivalent ion for the same colloid are in the 

 ratio 



Iv' : K 2 : K, 



or K- : K : J, 



