414 Investigations dealing with the State of Aggregation. 



Snum/mary. 



The theories regarding the flocculation of colloids by salts have been 

 discussed. To test the " adsorption hypothesis," the precipitating capacity of 

 salts containing organic ions, the normal solutions of which exhibit wide 

 variations in their surface tensions, was determined. It was expected, should 

 this hypothesis hold, that the salts giving solutions of lowest surface tension 

 would exhibit the greatest flocculating capacity. The following sodium salts 

 were employed : formate, acetate, lactate, mono-, di- and trichloracetate, 

 salicylate, benzoate, and benzene sulphonate. Also the following (hydro) 

 chlorides : sodium, ammonium, monomethylamine, trimethylamine, dimethyl- 

 amine, tetraethylammonium, piperidine, triethylamine, benzylamine, isoamyl- 

 amine, hexylamine. The following sols were used : ferric, zirconium and 

 eerie hydroxides, Victoria blue B, azo-blue, brilliant Congo-red R, scarlet 

 gold sol, arsenic sulphide, and mastic. 



In general, no relationship was found to exist between the surface tensions 

 of the normal solutions and the flocculating capacity of salts. When a series 

 of salts was compared in which the varying ion was not the active 

 precipitating ion, the precipitating limits were all within a comparatively 

 narrow range, in spite of the wide variations of the surface tensions of the 

 solutions. In the series, when the varying ion was the active ion, the range 

 was large, although the precipitating capacity could not be generally correlated 

 with the surface tension. The marked exception to this statement was shown 

 in the case of mastic, when precipitated by the (hydro)chlorides. In this 

 case the salts of low surface tension exhibit the greater flocculating poweijp 

 (with the exception of tetraethylammonium chloride). 



It is suggested that suspensoid colloids may be subdivided into classes : 

 (a) those, like ferric hydroxide, which owe their charge to association with 

 " active " ions derived from salts from which they have been prepared, which 

 are removed during aggregation, which results finally in flocculation, and 

 which may be termed " exionic colloids ; " (&) those owing their charge to the 

 dissociation of the colloid itself, in which a rapidly diffusing ion (such as 

 hydrogen ion) forms the outer layer, and is held electrostatically to a less 

 diffusible ion. These may be termed " endionic colloids." Mastic is probably 

 a colloid which belongs to this class. 



