88 ION SERIES AND PROTEINS. I 



show that the strong dibasic acid H2SO4 combines in equivalent pro- 

 portions with gelatin while the weaker acids, e.g. phosphoric or 

 oxalic, combine in molecular proportions. At a given pH, e.g. pH = 

 3.5, 1 gm. of originally isoelectric gelatin is in combination with three 

 times as much 0.1 n acid when the acid is H3PO4 than when it is 

 HCl; and with almost twice as much 0.1 n acid when the acid is oxalic 

 than when it is HCl ; while the ratio of HCl and H2SO4 is 1 . It follows 

 from this that the strong dibasic acid H2SO4 forms a salt with gelatin 

 in which the anion is divalent, namely SO4, while the weak tribasic 

 acid H3PO4 forms a salt with gelatin in which the anion is monovalent; 

 namely, H2PO4 (instead of the trivalent anion PO4). Likewise, citric, 

 succinic, and tartaric acids form gelatin salts in which the anion is 

 always monovalent; namely, H-succinate, H- tartrate, etc. In the 

 case of oxalic acid this is also the case though a slight amount of 

 gelatin salt with divalent anion is probably formed and this might 

 account for the fact that the osmotic pressure of gelatin oxalate is 

 generally slightly less than that of gelatin chloride.^ 



It was also found that Ca(0H)2 and Ba(0H)2 combine with gelatin 

 in equivalent and not in molecular proportion thus showing that the 

 cation of Ca gelatinate and Ba gelatinate is divalent.^ 



All these facts together show that solutions of salts of gelatin with a 

 bivalent ion have an osmotic pressure of one-half or less of that of 

 solutions of salts of gelatin with monovalent ions at the same pH and 

 the same concentration of originally isoelectric gelatin. 



This then proves that while the valency of the ion in combination 

 with the gelatin has a strong influence on the osmotic pressure of the 

 gelatin solution differences in the nature of ions of the same valency 

 have either no effect on the osmotic pressure or if they have such an 

 effect it is too slight to be noticeable by our method of experimen- 

 tation. We can certainly say that it is impossible to express our 

 observations in terms of the Hofmeister series. In the Hofmeister 

 series phosphates and chlorides stand at almost opposite ends of the 

 anion series while in our experiments the effects of H3PO4 and HCl are 

 identical if we compare the effects at the same pH of the gelatin solu- 

 tions. The reason that Pauli arrived at a different conclusion lies 



» Loeb, J., J. Gen. Physiol., 1918-19, i, 483. 



