BANCROFT. — POTENTIAL OF METALS. 



Ill 



measurements by Neumann,* and these are not conclusive as regards 

 the point that they were intended to prove, owing to an unfortunate 

 choice of sohitions. He measured the potential difference between 

 thallium and solutions of tluillium salts. Most of the salts were salts 

 of organic acids, and Ostwald f had already found that when the nega- 

 tive ion was an organic radical its nature was immaterial. To settle 

 this question one should take negative ions which show marked differ- 

 ences with non-reversible electrodes, such as chlorides, bromides, and 

 iodides. As the negative ion has a very marked influence in these last 

 named cases, and as there is no reason to su^jpose that the haloid salts 

 form a class by themselves, the simplest assumption is that the nega- 

 tive ion always has an effect, and that in the cases where this does not 

 appear, such as tlie organic radicals, we are measuring something 

 else which is the same in all cases. Le Blanc | found something 

 similar in his studies of polarization, where beyond a certain point he 

 obtained the value for the primary decomposition of water. 



There are certain quantitative relations connected with the change 

 of the negative ion which deserve to be brouglit out, and in Table XI. 

 are given the most probable values for the po ential differences of the 



TABLE XL 



TABLE XIL 



* Zeitschr. f. ph. Ch., XIV. 225, 1894. 

 t Ibid., I. 605, 1887. 



t Ibid., VIII. 315, 1891. 



