JACQUES LOEB 70l 



1. The curve for the calculated osmotic pressure of gelatin chloride 

 is identical with the curve for the calculated osmotic pressure of 

 gelatin phosphate, and the same is true for the two corresponding 

 curves representing the observed osmotic pressures (Figs. 1 and 2). 



2. The curve for the calculated osmotic pressure of gelatin sulfate 

 is a little less than half as high as the curves for the calculated osmotic 

 pressures of gelatin chloride and gelatin phosphate; and the same 

 is true for the curves representing the observed osmotic pressures of 

 gelatin sulfate and gelatin chloride. 



3. All the curves in Figs. 1 and 2 rise from a minimum at pH 4.7, 

 reach a maximum (which lies at pH 3.4 or 3.5 for the observed, and at 

 3.0 for the calculated curves), and then drop again as steeply as they 

 rose on the other side. Moreover, the absolute values of observed 

 and calculated osmotic pressures agree almost quantitatively, a fact 

 which will be discussed more fully in Chapter V. 



It may be added that the curve for the calculated values of the 

 osmotic pressure of gelatin oxalate solutions agrees also with the 

 curve for the observed values of the osmotic pressure of solutions of 

 the same gelatin salt, both being slightly lower than the curves for 

 gelatin chloride. 



We can therefore say that (with the exception of two minor dis- 

 crepancies to be discussed further on) the Donnan equilibrium 

 accounts not only qualitatively but almost quantitatively for (a) the 

 valency effect of the anion with which the gelatin is in combination; (6) for 

 the effect of the pH. 



Thus two of the most puzzling problems of the colloid chemistry of 

 proteins seem to find their solution on the basis of classical physical 

 chemistry. 



IV. The Presumable Osmotic Pressure of Gelatin Particles. 



The question now arises what the possible share of the protein 

 particles in the osmotic pressure may be. Different concentrations 

 of gelatin phosphate from 2 per cent to | per cent were prepared, all 

 having a pH of 3.5. The gelatin phosphate solutions were put into 

 Erlenmeyer flasks of 50 cc. volume, connected with a glass tube 

 serving as a manometer as described, and these flasks were put into 

 beakers containing 350 cc. of H2O, the pH of which was brought at 



