ELECTROLYTIC TAUTOMERISM 311 



INCREASING TENDENCY TO PREVENT PRECIPITATION OF ELECTRO-NEGATIVE 



ALBUMEN. 



The sign -I- indicates that the reagent precipitates albumen, and - that it 

 does not. 



If, however, we make an albumen solution electro-positive 

 by the addition of a little acid, the electro-negative or acid 

 radicles now become the precipitants, and the whole order is 

 reversed, and those salts which like the bromide, iodide or 

 sulphocyanide, tended to prevent precipitation, now become 

 the most powerful precipitants. 



AMPHOTERIC ELECTROLYTES. 



Amphoteric electrolytes are defined by Bredig * as sub- 

 stances which in aqueous solution are able to exhibit both acid 

 and basic properties, and are accordingly able to split off or 



combine with H or OH ions. 



Thus, in the presence of bases they behave as acids and 

 dissociate as follows : 



ROH ^ RO + H 



whereas in the presence of acids they behave like bases, giving 

 the following ions : 



ROH ;=; R + OH 



This phenomenon of changing electrolytic distribution ac- 

 cording to circumstances is known as " electrolytic tautomer- 

 ism ". Examples of amphoteric electrolytes in inorganic com- 

 pounds are to be found amongst the hydroxyl derivatives of 

 most of the elements from the middle of the periodic table, 



* Bredig: "Zeit. Electrochem.," 1899, 33. 



