76 



CHEMICAL STATICS 



quoted results of Bugarzsky and Liebermann, it is evident that, 

 save in the presence of a considerable excess of neutral salts, 

 little or no alteration in the freezing-point of the solution would 

 result from the addition to it of protein, since the depression of 

 conductivity observed by Hardy only amounted to 2 per cent 

 of that of a A^/10 solution, and the cryoscopic method is not 

 sufficiently sensitive to reveal, with certainty, such slight varia- 

 tions in the freezing-point of solutions. For this purpose the 

 method of electrical conductivity is much to be preferred. An 

 alternative interpretation of these results will be found in Chap. VI. 



7. The Potentiometric Method. — This method is also based 

 upon the fact that the addition of protein to a solution of a strong 

 base or acid diminishes the concentrations of the ions of the 

 inorganic constituent of the mixture. As in the previous methods, 

 the measurement is static. But, instead of involving the meas- 

 urement of the total ionic or ionic plus molecular concentration 

 of the mixture this method enables us to directly determine the 

 concentration of a given ion. The results are therefore much 

 more readily interpreted than those obtained by the two methods 

 previously described and, indeed, furnish us with a direct meas- 

 ure of the quantity of a (highly dissociated) base or acid which 

 is actually bound in the solution, by the protein. For a brief 

 description of the principles underlying potentiometric measure- 

 ments in concentration-chains the reader is referred to the appen- 

 dix; for fuller details to such works as those of Hamburger (15) 

 and Michaelis (29).* 



The potentiometric method was first employed for this pur- 

 pose by Bugarzsky and Liebermann (5). These investigators 

 employed two different concentration-chains. The one, the 

 mercury-chain, was built up as follows: 



In the first instance the potential of the chain for a certain con- 

 centration of HCl in 2 was measured, then a weighed amount 



* For the modifications in technique imposed by the presence of proteins 

 in the solutions under investigation vide Appendix. 



