614 COLLOIDAL BEHAVIOR OF EDESTLNf 



showed that the same was true for the chloride of egg albumin. On 

 the basis of Donnan's theory he devised a method^^ of calculating the 

 osmotic pressure of a protein-acid salt solution from measurements 

 of the hydrogen ion concentration. The calculation, which neglects 

 the unknown osmotic pressure of the protein itself, gives the following 

 expression for the osmotic pressure in the case of a protein-acid salt 

 with univalent anion: 



Osmotic pressure at 24°C. = 2.5 X 10^ (2y + z — 2x) mm. of water. 



Here y is the hydrogen ion concentration of the inside solution, x that 

 of the outside solution, and z the concentration of anion from the 

 protein-acid salt, all being expressed in moles per liter. Since accord- 

 ing to Donnan's theory 



*^ = y Gy + ») 



the expression for osmotic pressure reduces to 



2.5 X 10^ X ^^ — 



y 



In applying this calculation to gelatin chloride, Loeb found that the 

 curves representing osmotic pressure as a function of pH were of the 

 same general shape and height as the observed curves, but had maxima 

 at a lower pH. A calculation made from his results on albumin 

 chloride^** yielded similar results. 



Fig. 8 represents the effect of pH on the observed and calculated 

 osmotic pressure of a 0.45 per cent solution of edestin chloride. The 

 curve for observed osmotic pressure has a maximum at a lower pH than 

 that for observed p.d. shown in Fig. 5, while the curve for calculated 

 osmotic pressure has a maximum at a still lower pH. Thus the 

 behavior of edestin in these respects exhibits the same peculiarities 

 which Loeb observed with gelatin and egg albumin. 



SUMMARY. 



1. It has been shown by titration experiments that the globulin 

 edestin behaves like an amphoteric electrolyte, reacting stoichio- 

 metrically with acids and bases. 



" Loeb, J., /. Gen. Physiol, 1920-21, iii, 691. 



