74 



CHEMICAL STATICS 



be employed in investigations such as those cited above, in the 

 place of calcium phosphotungstate. von Rhorer has employed 

 potassium mercury iodide (K2Hgl4) and calcium picrate. 



5. The Method of Electrical Conductivity. — This method is 

 based upon the fact that the salts of the proteins are, in solution, 

 less highly ionized than the majority of the strong inorganic 

 acids or bases in equivalent concentration. Hence on adding 

 proteins to a solution of one of these latter, the total number 

 of ions per liter of the solution is diminished. Moreover, the 

 protein ions which are formed have a low velocity of migration 

 (16) (37) (38) (40) (41) as might be anticipated, having regard 

 to the magnitude of their mass and volume. Hence, on adding 

 protein to a solution of a strong acid or of a strong base, the 

 conductivity of the solution is diminished and this diminution 

 affords a measure of, although it is not directly proportional 

 to, the quantity of acid or base bound by the protein. This 

 method was first employed in a systematic manner by Sjoqvist 

 (47) . The following figures are illustrative of his results : 



The molecular conductivities were calculated for a 0.025 m. 

 HCl solution. It will be observed that after a certain quantity 

 of albumin has been dissolved in the acid (4.25 per cent) the 

 molecular conductivity of the solution approaches constancy, 

 indicating that all of the acid is bound by the protein; the infer- 

 ence being that the conductivity thereafter measured is that of 

 the protein hydrochloride alone, the addition of further albumin 

 contributing but little to the conductivity of the solution, since 

 free, unneutralized protein is but sparingly ionized. 



Details of more recent results obtained by this method and 

 their interpretation will be found in the chapters dealing with 

 the electrochemistry of the proteins. Since this measurement 

 is a static one, the objections which apply to the two methods 

 previously described do not apply to it. 



6. The Cryoscopic Method. — This method depends upon the 

 diminution in the total ionic + molecular concentration in solu- 



