70 THEORY OF COLLOIDAL BEHAVIOR 



that the osmotic pressures of the two salts should be identical 

 and a glance at Fig. 14 shows that this is the case. The anion 

 of gelatin oxalate should also be essentially monovalent for pH 

 below 3.0 and we see that the descending branch of the oxalate 

 curve, from pH 3.0 and below, practically coincides with the 

 descending branch of the curve for gelatin chloride and phos- 

 phate. For pH above 3.0 the curve for the osmotic pressures of 

 gelatin oxalate is slightly lower than the curve for gelatin phos- 

 phate and gelatin chloride, as the theory of electrolytic dissocia- 

 tion demands, since for pH above 3.0 oxalic acid dissociates 

 electrolytically more and more like a dibasic acid the higher 

 the pH. Hence, at about pH 3.4 the majority of the anions of 

 gelatin oxalate is monovalent, but a certain small percentage is 

 divalent. For this reason the curve for gelatin oxalate is at 

 pH 3.4 or for higher pH not quite as high as that for gelatin 

 chloride or phosphate. This is in strict agreement with the 

 titration curves in Fig. 7. 



The titration curves in Fig. 7 show also that H 2 S0 4 forms a 

 divalent anion in combining with gelatin and we notice that the 

 maximum of the osmotic pressure curve at pH 3.4 is less than 

 one-half that of the osmotic pressure curve for gelatin chloride 

 or gelatin phosphate at the same pH. 



These results are then in full agreement with the titration 

 experiments if we assume that only (or chiefly) the sign and the 

 valency of the ion with which the protein is in solution determine 

 the osmotic pressure of the protein salt formed, while the nature 

 of the ion has either no effect or if it has any effect the latter must 

 be so small that it escapes detection. 



If the Hofmeister series were correct, we should have expected 

 that the curve for the osmotic pressure of gelatin phosphate 

 should have been of the order of that of gelatin sulphate or even 

 lower instead of being equal to that of gelatin chloride; and the 

 same should have been true for the curve for gelatin oxalate. 



I have repeated these experiments so often that there can be 

 no doubt about the correctness of the result. 



The experiments with 1 per cent solutions of originally isoelec- 

 tric crystalline egg albumin confirm the valency rule also for 

 this salt. 1 The abscissae are again the pH determined at the 

 , J., J. Gen. PhysioL, vol. 3, p. 85, 1920-21. 



