I909.] 



The Dialysis of Colloidal Ferric Hydroxide. 



57 



to a large extent by the chlorine. However the fact that, as the amount 

 of chlorine in the solution is increased beyond a certain limit, the charge 

 on the particle begins to decrease again, shows that, in such a solution, 

 we are dealing with a very complex set of phenomena ; further, any work 

 on the coagulating power of salts with such solutions as this would depend 

 on the stage at which the dialysis had been carried. 



Similar experiments were performed on soluble Prussian Blue (Ber- 

 liner Blau). The dialysis and measurement were carried on just as in the 

 case of the ferric hydroxide. The corresponding results are given in 

 Table II and illustrated in the curve of Figure 2. A glance at these will 

 show that the same effect is apparent with this second colloidal solution. 

 The charge seems to be due to some absorbed potassium ferrocyanide 

 which then plays the part of the ferric chloride in the colloidal ferric hy- 

 droxide. In the case of the ferrocyanide the stabilizing ion is the potassium 

 and the particles are charged negatively, while as is well known the ferric 

 hydroxide particles are positively charged. 



Table II. — (Prussian Blue.) 



h. Effect of Potassium Phosphate on Ferric Hydroxide. 

 Papers have been published by the writer (5) in which the action 

 of added electrolytes on the velocities of the colloidal particles has been 



(5) Phil. Mag. S. 6, Nov. 1906, and April 1909. 



