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



belonging to the molecule of the substance itself, which is the main or 

 perhaps the only body, apart from water of hydration, in the colloid phase. 

 The colloid may be, e.g., an acid substance containing carboxyl groups which 

 will dissociate into readily diffusible hydrogen ions and large slightly 

 diffusible cations. The former would then exist in the outer layers of the 

 colloid phase, and be held electrostatically to the slowly moving cation in 

 the inside. Mastic (a resin acid) is probably the only substance investigated 

 which would form a sol of this class, and it is noteworthy that in this case 

 only is there a close relationship between the surface tensions of their 

 solutions and the flocculating capacity of salts. It is proposed to designate 

 colloids of this class as endionic and those of the other class exionic. It is 

 hoped, at a more favourable opportunity, that these investigations may be 

 extended to other substances, such as the proteins, which probably belong to 

 this class. Pressure of other work and difficulty in obtaining the requisite 

 materials are, for the moment, obstacles to such an extension. 



Surface Tensions of Normal Solutions. 



The materials employed were, when obtainable, Kahlbaum's prepara- 

 tions. The dichloracetic acid was prepared in the laboratory from chloral- 

 hydrate by Wallach's method. The lactic acid was obtained from a crude 

 commercial specimen by recrystallisation of the calcium salt and its sub- 

 sequent decomposition by anhydrous oxalic acid (in slight deficiency) in 

 pure ether. Mono- and trimethylamine were obtained in a satisfactory state 

 of purity as hydrochlorides by a method recently described by Werner.* 

 The corresponding salt of dimethylamine, in spite of several attempts, could 

 not be obtained pure by Werner's method, and the base was finally prepared 

 by the action of sodium hydroxide on dimethylaniline. The authors are 

 indebted to Prof. Philip for a sample of triethylamine and tetraethylam- 

 monium bromide, from which latter substance the chloride was prepared 

 in the usual manner. The surface tensions of the sodium salts are quoted 

 from the first paper of this series, with the exception of that of benzene 

 sulphonic acid. The surface tensions of this and the other substances in the 

 Table were determined by the drop method with the use of a Traube stalag- 

 mometer. The specific gravities were determined in a small pycnometer. 

 The sodium salt solutions were made by the method described in the first 

 paper. The chloride solutions were standardised by silver nitrate. The 

 usual precautions for obtaining sufficiently pure water were taken. 



* ' Trans. Chem. Soc.,' vol. Ill, p. 844 (1917). 



