Investigations dealing with the State of Aggregation. 405 



cases the active ion is the cation; on the other hand, the precipitating 

 capacity of the hydrochlorides of bases varied only within narrow limits in 

 spite of the wide variations in the surface tension of the normal solutions. 

 In the case of the negative sols wide variations were observed in the action 

 of the hydrochlorides but not in the case of sodium salts. The ferric 

 hydroxide sol was flocculated more readily by the sodium salts of weak 

 acids than by the corresponding salts of strong acids, and the same fact 

 holds, though with some exceptions, to the action of these salts on other 

 sols prepared by the dialysis of salts of inorganic acids. These facts might 

 suggest that in the case of the ferric hydroxide sol the colloidal phase 

 might consist of a heavily hydrated ferric hydroxide {cf. researches of 

 van Bemmelen) holding ferric chloride, water, and hydrochloric acid in 

 chemical equilibrium with one another : — 



■ FeCls + 3H2O Fe(0H)3 + 3HC1, 



and that the sodium salt of a weak acid would react with the hydrochloric 

 acid with the formation of sodium chloride and a free slightly dissociated 

 organic acid and thus lead to the discharge of the colloid phase. Until more 

 is known, however, as to the distribution of electrolytes between a hydrated 

 colloid phase and the dispersion medium, a problem which involves the con- 

 sideration of several factors (see Schryver and Hewlett loc. cit.), discussion on 

 this matter is of little value. The results found generally do not support 

 the adsorption hypothesis of the flocculating action. 



In only one case, and the exception appears to be an important one, is 

 there any marked relationship between the surface tension of the salt 

 solution and the flocculating capacity of the salts, and it is that of the action 

 of the hydrochlorides on the flocculation of mastic. In this case the salts 

 giving solutions with the lower surface tensions have the greater precipita- 

 ting power. Only one salt, viz., tetraethylammonium chloride falls out of 

 the series and this is different chemically from the hydrochlorides. 



This fact seems to suggest that a differentiation may be made between the 

 various suspensoids colloids which takes into account the origin of the 

 electrical charge. In the case of a sol such as ferric hydroxide, the stability 

 depends upon the association of the sol with " active " ions, derived from 

 the salt from which the colloid is prepared (CI' ions when ferric hydroxide 

 sol is prepared from ferric chloride, and NO3' ions when prepared from the 

 nitrate). As the ions are gradually removed by hydrolysis, the stability 

 of the sol decreases. Aggregation resulting finally in flocculation is here 

 accompanied by a marked change in the components of the colloid phase. 

 But it is conceivable that sols can exist in which the charge is due to ions 



