﻿Electrolytes on Colloidal Solutions. 177 



the aluminium salt is completely ionized, and therefore, 

 assuming that all the metal ions go to neutralize the charges 

 on the particles, we can determine the charge on each 

 particle if we know the number in solution. From a large 



Fisr. 1. 



| 80 







1 



1 







! 



Silver 



Cold 1 







t 



4\ 

















^s,^ 





















\ 





















\ 



















Si *©. 



















^^ 























































'•x.^ f^^ 





































"i -- 































































































^S 1 — ^ 



.50 20 10 10 20 30 



Velocity (cms xio' i ) 



number of determinations of the size of these silver particles, 

 we may take their average volume to be 2 x 10~ u c.cs., so 

 that since there was 6*5 mgs. of silver per 100 c.cs. of solution, 

 there were 3 x 10 10 particles per 100 c.cs. So that the 

 charge carried by 26 X 10~ 6 grs. aluminium ions is just 

 sufficient to neutralize the charge carried by o x 10 10 particles. 

 Therefore the charge on each particle is 2'S x 10~ 2 electrostatic 

 units. 



From the amount of aluminium necessary to neutralize the 

 charges on the silver and gold particles, we may calculate the 

 total charge corresponding to a gram equivalent of silver and 

 gold in the colloidal state in water : — 



(a) Charge on gram equivalent of colloidal silver = *01 of 



charge corresponding to a gram equivalent of a 

 univalent ion. 



(b) Charge on gram equivalent of colloidal gold = '12 of 



charge corresponding to a gram equivalent of a 

 univalent ion. 



5. The Reversal of the Charge on the Particles. 



A very striking result of these experiments is the fact that, 

 after passing through the isoelectric point, an increase in the 

 quantity of electrolyte added produces an increase in the 

 stability of the solution. When the minutest traces of 



