CHAPTER V 

 THE COMPOUNDS OF THE PROTEINS (Continued) 



1. Stoichiometrical Relations in Protein Compounds. — With 

 the aid of the various methods outhned in the previous chapter, the 

 existence of a number of compounds of the proteins with inorganic 

 acids, bases and salts has been conclusively demonstrated. Of 

 these compounds, however, comparatively few have been exten- 

 sively studied, and in equally few cases have the stoichiometrical 

 relations which pertain between the constituents of the compounds 

 been elucidated. This is due in part, no doubt, to the complexity 

 and amphoteric character of the proteins themselves, and in part 

 to the difficulty of sharply characterizing and of isolating the 

 individual proteins in a pure condition, but in the main, I believe, 

 to the fact that physical chemistry has only recently been in a 

 position to supply us with the implements which the investigation 

 of these compounds demands. We have seen that the successful 

 investigation of these compounds requires, as a rule, the employ- 

 ment of static methods of measurement; methods, that is, which 

 do not involve a disturbance of the equilibria in the system while 

 these equilibria are being determined. Many investigators in this 

 field have, in the past, employed methods of determining the exist- 

 ence of protein compounds, which, to our modern perceptions, 

 clearly involved a variable and uncontrolled interference with the 

 very equilibrium which was the subject of investigation. Exam- 

 ination of more modern literature, however, cannot fail to impress 

 the reader with the conviction that in proportion to the adequacy 

 of the chemical or physico-chemical technique employed, stoi- 

 chiometrical relations between the proteins and the substances with 

 which they combine are revealed or indicated. 



The problem of determining the nature of the compounds 

 formed by the proteins with inorganic acids or bases is complicated 

 by the fact that, as a rule, a protein can combine with not only one 

 but several equivalents of a base or acid, so that on adding acid or 

 alkali to a solution of a protein we obtain a continuously varying 

 mixture of the various possible salts. Precisely analogous phenom- 



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