CORRECTNESS OF THE CHEMICAL VIEWPOINT 43 



It can be shown by titration experiments that acids and bases 

 combine with proteins in the same way as they combine with 

 crystalline compounds, namely, by the purely chemical forces 

 of primary valency. It is known that a weak dibasic or tribasic 

 acid gives off one hydrogen ion more readily than both or all 

 three, and that it depends on the hydrogen ion concentration of 

 the solution whether one or two or three H ions are dissociated 

 from a tribasic acid. Thus H 3 PO 4 will give off only one H ion 

 as long as the pH is below 4.6. Oxalic acid, which is a stronger 

 acid, will act like a monobasic acid below a pH of about 3.0, 1 

 while above this pH it acts more and more like a dibasic acid. 

 In a strong dibasic acid, like H 2 SO 4 , both H ions are held with so 

 small an electrostatic force that even at a pH of 3.0 or consider- 

 ably below the acid acts as a dibasic acid. If the forces which 

 determine the reaction between these acids and proteins are 

 purely chemical, it would follow that three times as many cubic 

 centimeters of 0.1 N H 3 PO 4 should be required to bring 100 c.c. 

 of 1 per cent solution of isoelectric gelatin to a given pH below 

 4.6, e.g., 3.0, as are required in the case of HNO 3 or HC1; while it 

 should require just as many cubic centimeters of 0.1 N H 2 SO 4 as 

 of 0.1 N HC1. Twice as many cubic centimeters of 0.1 N oxalic 

 acid should be required to bring isoelectric gelatin to a pH of 

 3.0 or below, as are required in the case of HC1. It can be shown 

 that these predictions are true. 2 



2. Crystalline egg albumin was prepared according to S0rensen's 

 method, 3 and crystallized three times. The only difference in 

 procedure was in the dialysis. Instead of putting the water 

 under negative pressure, as was done by S0rensen, pressure was 

 put on the egg albumin by attaching a long glass tube full of 

 water to the dialyzing bag so that the solution was under about 

 150 cm. water pressure during dialysis. This was necessary to 

 avoid too great an increase in volume. The same stock solution 



1 HILDEBRAND, J. H., J. Am. Chem. Soc., vol. 35, p. 847, 1913. See 

 also MICHAELIS, L., "Die Wasserstoffionenkonzentration," Berlin, 1914; 

 CLARK, W. M., "The Determination of Hydrogen Ions," Baltimore, 1920. 



2 The experiments to be described are from LOEB, J., J. Gen. Physiol., 

 vol. 3, p. 85, 1920-21. 



3 S^RENSEN, S. P. L., Studies on proteins: Compt. rend. trav.Lab. Carlsberg, 

 vol. 12, Copenhagen, 1915-17. 



