206 ELECTROCHEMISTRY 



of HCl bound by ovomucoid at absolute neutrality, estimated 

 in the above manner, is 7 X 10~^ equivalents per gram. 



3. The Non-Dependence of the Composition of the Compounds 

 of Protein with Acids and Bases upon the Dilution of their 

 Solutions. — The view would appear to be very generally held 

 (35) (9) (51) that the salts which proteins form with acids and 

 bases are subject in a very high measure to hydrolytic dissoci- 

 ation. This view is nevertheless erroneous. When a base unites 

 with an organic acid to form a salt by the neutralization of a 

 — COOH group the reaction may be expressed as follows: 



R.COOH + KOH ;=± RCOOK + H.OH. 



If the acid is a very strong one then the reaction will proceed 

 completely from left to right and the salt will not be appreciably 

 decomposed by dilution. If, however, the acid is tolerably weak 

 (e.g., acetic acid) so that the water itself, acting as an acid, is 

 able, if present in large amounts, to displace it partially from its 

 combination with the base, then the reaction will not proceed 

 completely from left to right but will pause, in accordance with 

 the mass law, in a condition of balance, which is shifted towards 

 the right by the addition of excess of base and towards the left 

 by dilution. On adding excess of base to a dilute solution of an 

 acid of this type, therefore, more of the base will be observed 

 to be neutralized, while the addition of water will result in partial 

 decomposition of the salt. Similar considerations hold good, of 

 course, for the salts of weak bases. When one examines the 

 evidence which has been brought forward by different observers 

 in support of the thesis that protein salts are subject to hydrolytic 

 dissociation one finds that it is all of the first kind, that is, con- 

 sists in the fact that upon the addition of more acid or base to the 

 protein solution, or of more protein, more of the acid or base is 

 bound. From this the somewhat illogical assumption has been 

 made that the protein salts must exhibit the other characteristic 

 property of salts of weak acids and bases, namely, decomposa- 

 bility by water. We have, however, seen that the fact that pro- 

 tein will bind more of an acid or a base in the presence of an 



This mode of dissociation would, of course, be prevented by dissociation of the 

 molecule through its — N.HOC— groups, and, since this is brought about 

 by the addition of acid, the addition of small quantities of acid might well 

 decrease the acidity (H+ concentration) of the solution. 



