220 Prof. L. Kahlenberg on the 



<^ 



chemical analysis have been regarded as taking place between 

 the ions in the solutions, and the fact that these reactions 

 proceed practically instantaneously in most cases, has been 

 ascribed to the peculiar electric properties which the ions are 

 supposed to possess. But 1 have shown * that when copper 

 oleate is dissolved in benzene and treated with HC1, PC1 3 , 

 AsCl 3 , SnCl 4 , or SiCl 4 , also dissolved in the same solvent, 

 cupric chloride is precipitated in each case exactly as silver 

 chloride is thrown down from an aqueous silver-nitrate solu- 

 tion by soluble chlorides. And furthermore, a slight excess 

 of the precipitant in the case of the benzene solutions men- 

 tioned, yields more complete precipitation, just as it does in 

 aqueous solutions. The benzene solutions mentioned are all 

 excellent insulators. It is therefore demonstrated that the 

 instantaneous reactions observed in aqueous electrolytic solu- 

 tions cannot be ascribed to the fact tbat these solutions con- 

 duct electricity — or, in the language of the dissociation theory, 

 to the presence of free ions — for exactly similar reactions 

 occur in solutions that are the best of insulators. Such views, 

 then, as are presented in Ostwaid's ' Scientific Foundations 

 of Analytical Chemistry,' and are echoed by various other 

 writers, cannot be maintained. 



According to the dissociation hypothesis, solutions of acids 

 are supposed to owe their characteristic properties to the 

 presence of hydrogen ions. Now it is well known that tri- 

 chloracetic acid, when dissolved in water, yields an excellent 

 electrolyte, and exhibits the properties of a fairly strong acid. 

 In the course of an investigation f on the electrical conduc- 

 tivity of solutions in sulphocyanates and mustard-oils, 1 

 showed that a normal solution of trichloracetic acid in allyl 

 mustard-oil is a poorer conductor than the purest water 

 which Kohlrausch ever prepared in contact with air, and yet 

 this solution attacks dry magnesium rapidly, and decomposes 

 the dry carbonates of sodium and potassium. It is well 

 known that even ordinary distilled water attacks magnesium 

 quite slowly, and of course does not evolve carbon dioxide 

 from alkaline carbonates. However, judging from the con- 

 ductivity test, water contains more hydrogen ions than the 

 solution of trichloracetic acid in allyl mustard-oil, and ought 

 to show more vigorously the characteristic action of the 

 hydrogen ion. 



In physiological investigations, too, the theory of electro- 

 lytic dissociation has proved inadequate ; so, for instance, it 

 has been found that dilute solutions of acid salts are sourer 



* Joum. phys. Chem. vi. p. 1 (1902). 

 f Zeit.phys. Chem. xlvi. p. 64 (1903). 



