404 



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



the anions, it was necessary to investigate in addition the influence of the 

 surface tension of sohitions of a series of salts containing a common anion. 

 For this purpose the hydrochlorides of organic bases were chosen. As many 

 of these have only a low basic dissociation constant, their hydrochlorides 

 undergo an appreciable amount of hydrolytic dissociation in water, and this 

 introduces a complication which it is desirable to avoid. For this reason, 

 only those bases are included within the sphere -of investigation, of which the 

 basic dissociation constants are greater than that of ammonia.* 



Before proceeding to discuss the results obtained, it is necessary to refer 

 to another possible influence of the action of the surface tension of solutions 

 on the process of aggregation of colloids. If adsorption is the main factor in 

 production of the flocculation, it would follow that the lower the surface 

 tension the smaller the concentration of the salt solution necessary to 

 produce the requisite amount of discharge and consequent aggregation. The 

 lowering of the surface tension at the interface colloid-dispersion medium 

 might conceivably tend to act against aggregation, so that two possible 

 actions might be ascribed to the surface tension effect, which are anti- 

 batic. Zsigmondy, however, in a very recent paper,f has expressed the 

 opinion that surface tension effects play but little part in the aggregation in 

 the case, at any rate, of the suspensoid colloids, and that the process takes 

 place by direct attraction of the colloids particles as soon as the potential 

 difference between these and the dispersion medium has been reduced below 

 a certain critical maximum.^ The dynamics of aggregation has been mathe- 

 matically treated on this assumption by the late E. von Smoluchowski, and 

 forms the subject of one of the last papers published by him before his 

 death.§ Under any circumstances, the surface tension at the interface 

 suspensoid colloid-dispersion medium is probably high, and the relative 

 amount of lowering produced by the addition of the quantity of salt necessary 

 to bring about aggregation is so small that the mechanical effect of surface 

 tension acting against flocculation is probably quite negligible. This suppo- 

 sition is borne out by experiments recorded in the sequel. 



As a general result of these investigations, it was found that there is 

 generally no relationship between the surface tensions of solutions of salts 

 and their flocculating capacity. In the case of positive sols, wide variations 

 were found in the precipitating capacity of the sodium salts, as in these 



* Reference was made to Lunden's tables for this constant ; no record was found of 

 K{ for hexylamine. From analogy one would judge that it is of the same order as that 

 of ammonia. 



t ' Zeitsch. Physikal. Chem.,' vol. 92, p. 600 (1918). 

 I ' Zeitsch. Physikal. Chem.,' vol. 92, p. 129 (1917). 

 § Powis, loc. cit. 



