determine the Stability of Irreversible Hydrosols. 



123 



action exerted by the reagent in virtue of its alkalinity, the result is 

 that the coagulative concentration of the alkali Ba(0H)2 gives a value 

 for K which is less than that given by salts of bivalent metals, and the 

 specific conductivity of the solution is of the same order as that of the 

 coagulating concentration of salts of univalent metals. Against these 

 suggestions, however, must be set the anomalous relations of the 

 various alkalis to the hydrosol of gold. 



Action of a Salt in p-esence of Varying Amounts of Acid or Alkali. 



This was measured for one salt only, potassium sulphate, the col- 

 loidal solution being gold. The figiires are as follows : — 



Temperature 16° 



Concentration of the salt ne- 



Acetic acid. 



Ammonia 



Concentration 



cessary to produce blue tint. 



1 gr.-mol. in — 



1 gr.-mol. K2SO4 in — 



c.c. 



c.c. 



1,087 







16,000 



324,000 



• 66,000 



64,000 



330,000 



50,000 



(neutral*) 



28,500 



113,333 



10,000 



22,666 



9,000 



4,900 



20,000 



2,450 



24,000 



980 



20,000 



200 



Large amount of salt needed. 



100 



Salt unable to act when saturated 



at 16° or at 100°. 



These results are shown in the curve. Ammonia alone will not 

 aggregate the particles of gold. Up to a certain point, however, it 

 decreases the stability of the system. 



The conclusions can be summarised as follows : — The irreversible 

 hydrosols which have been investigated are systems composed of solid 

 particles dispersed through a solution of the substance of the solids 

 in the water. 



The stability of the system is related to the contact difference of 

 potential which exists between the solid and the fluid phases, and 

 which forms round each solid particle a double electrical layer. Such 

 double electric layers round particles of any kind immersed in a iluid 



* Except for ? faint acid reaction of th'e gold solution, due probably to a trace of 

 phosplioric acid. 



