So COLLOID CHEMISTRY OF THE PROTEINS 



CHAPTER VI 

 SALTS OF ALBUMIN AND ACIDS (continued) 



THE question of the hydrolytic dissociation of the albumin 

 salts is very important for a complete understanding of these 

 substances. It is well known that the salts of weak acids or of 

 weak bases have the property of reacting in aqueous solution 

 with formation of notable quantities of free acid and base. 



In accordance with the equation : 



BS + H 2 ; SH -f BOH . . . (i) 



if the acid is the stronger the hydrion concentration is increased 

 owing to the dissociation : 



SH=;S'-f- H-, 



or, if the base is stronger than the acid, the greater ionisation 

 of the former gives rise to more OH' ions. In the presence of 

 excess of one of the products of hydrolysis, the hydrolytic 

 dissociation is repressed in accordance with the law of mass 

 action, so that in equation i the reaction is reversed in the 

 direction of the upper arrow, i.e. from right to left. The fact 

 that the combination of albumin with acids or alkalis increases 

 with excess of acid or of alkali lends support to the view that 

 the protein functions as a weak base or weak acid under these 

 conditions, and so the addition of free acid or base respectively 

 opposes the hydrolytic dissociation of the albumin salt. This 

 view, notwithstanding the lack of convincing quantitative 

 measurements, held the field until recently (for literature see 

 Cohnheim, " Chemie der Eiweisskorper," 3 e Auflage). 



Robertson (loc. cit.), after his work on casein, opposed this 

 conception and decried altogether the hydrolytic dissociation 

 of the albumin salts. As a matter of fact, the behaviour 

 throughout is not nearly as simple as would appear from the 

 usual descriptions of it, and on account of the importance of 

 the matter it will now be further considered. 



