28 PHYSICAL CHEMISTRY 



hausted more are formed, and the whole process is instantaneous 

 in the above case. In this it is distinguished from the hydrolysis 

 of proteins, for instance, in which the protein is boiled for a long 

 time with acid or alkali, or hydrolyzed by means of enzymes. 

 In the salt hydrolysis water is all that is necessary, but in the 

 case of proteins the hydrolysis occurs with unmeasurable slow- 

 ness in pure water. 



Some substances may dissociate both H" and OH', and are 

 therefore called amphoteric electrolytes or ampholytes. The 

 amino acids and proteins belong to this class. Their general 

 formula is NH 2 RCOOH, in which R represents a carbon chain 

 (or a series of them connected by the amino and carboxyl 

 groups). Some of these may be about neutral, but usually the 

 acid or basic character predominates. The double nature of 

 these substances is shown by their compounds. If HC1 is added 

 to egg albumin the latter no longer dissociates H ions, owing 

 to the large number already in solution, but it continues to dis- 

 sociate OH ions and as fast as these are formed their place in 

 the albumin is taken by CI ions, so that more OH ions continue 

 to form and to combine with the H ions in solution. In this way 

 Alb. CI is formed, which dissociates into Alb" and CI'. If an 

 electric current is passed through the solution the albumin will 

 go to the cathode. 



On the contrary, if KOH is added to an albumin solution 

 Alb.K will be formed by the displacement of the H of the 

 hydroxyl, and if an electric current is passed the albumin will 

 go to the anode. 



At a certain reaction of the solution the albumin will not 

 migrate in an electric field, or if it does half will go toward the 

 cathode and half toward the anode. This reaction is called the 

 isoelectric point for that albumin. This subject will be con- 

 tinued in Chapter IV. 



