402 



Dr. S. B. Schryver and Miss N. E. Speer. 



hydroxide sols, which they regard as complex salts ; that prepared from ferric 

 chloride solutions they conceive as being built up according to the formula 



xFe(0B.)3.yYe--- SyCY, 



and as being a moderately strong electrolyte. On addition of a salt 

 containing an anion in common, e.g., sodium chloride, the dissociation of the 

 colloid is' depressed. The coagulating power of other electrolytes appears to 

 be determined by the solubiUty product of the colloid ion and the anion of 

 the coagulant. The depression of the dissociation is associated with 

 instability of the sol. The conceptions of Pauli and Matula are founded 

 mainly on what appear to be careful electrometric measurements of chlorine 

 and hydrogen ion concentration, but it must be urged in criticism of these, 

 that their value is uncertain when applied to what are undoubtedly hetero- 

 geneous systems. 



Now if the flocculation of colloids by salts is due, in the first instance, to 

 an adsorption process, some relationship between the flocculation concentra- 

 tion and the surface tension of the salt solutions should be expected; the 

 lower the surface tensions of the solutions, the greater should be the 

 .precipitating power. If, on the other hand, a double decomposition involving 

 the " active " ion of the colloid and the corresponding ion of the precipitant, 

 as postulated in the conceptions of Pauli and Matula and of Duclaux, is an 

 essential feature, no such relationship should exist. In the latter case, 

 furthermore, the relative precipitating capacity of salts belonging to a series 

 should vary from colloid to colloid. 



To investigate the relationship between surface tension of salt solutions 

 a,nd their capacity for flocculating colloids, salts containing organic ions were 

 chosen, as their normal solutions display wide variations in the first-named 

 property. A certain number of isolated experiments on flocculation by such 

 salts have been published in the literature, but no systematic examination on 

 a wide basis has been recorded.* 



For the present work, .a series of sodium salts was selected in the first 

 instance, which had been previously employed in determining the relation- 

 ship between surface tension and disaggregating power. This included the 

 following, which are placed in order of diminishing surface tension of their 

 normal solutions : Formate > acetate > lactate > monochloracetate > di- 

 chloracetate > trichloraeetate > salicylate > benzoate. The disaggregating 

 action of these salts shows a close relationship with the surface tension of 



* See e.g., Freundlich, ' Zeitsch. Physikal. Chem.,' vol. 44, p. 144 (1903) ; Picton and 

 Linder, ' Trans. Chem. Soc.,' vol. 87, pp. 1922 (1905) ; Traube and Onodera, ' International. 

 Zeitsch. fiir Physik.-chem. Biologie,' vol. 1 (1914). 



