ALKALOIDAL REAGENTS, ETC. 145 



did not react at all. For the tetrapeptid triglycyl glycin the 

 ratio is 3^. 



When CO2 is passed into a solution of a protein in Ca(0H)2 

 the conductivity of the mixture diminishes. From this Siegfried 

 draws the conclusion that the proteins react with carbonates 

 to form carbamino acids. From what has been said in the pre- 

 vious chapter concerning the mode of combination of proteins 

 with salts, however, the reader will gather that the validity of 

 this conclusion does not admit of being estabhshed in so simple 

 a manner. 



4. Compounds of the Proteins with the Alkaloidal Reagents, 

 Dyes, Alkaloids, etc. — In order that a protein may react with 

 an acid which is insufficiently dissociated to break up its 

 — N.HOC— groups, some stronger acid must be present, com- 

 bined with the protein, and which can then be displaced by the 

 weaker acid through the agency of one of its more strongly ionized 



salts. Thus : 



H 



I ++ 

 -N.HOC- + HA = -N"+ HOC- 



H H 



I ++ I ++ 



-N" + HOC- + BA' = -N" + HOC- + BA 



I I 



A A' 



HA being a strong acid, HA' a very weak acid, and BA' a salt 

 of that acid. Similar remarks apply, of course, to very weak 

 bases. Hence it is observed that proteins will combine with 

 very weak acids or with the acid radical of salts more readily 

 in acid than in neutral or alkaline solution, and with very weak 

 bases or the basic radical of salts in an alkaline rather than a 

 neutral or acid medium. Similarly a protein may not be able 

 to decompose a salt of an acid, binding the acid (or base as the 

 case may be), but, in the presence of a free acid it may be able 

 to do so, partly because the first acid is partially set free from 

 its salt by the second, but also because the ionization of the 

 protein is increased. 



