100 ELECTRIFICATION OF WATER AND OSMOTIC PRESSURE 



IV. The Gelatin Cation. 



When the hydrogen ion concentration of the gelatin solution is 

 higher than 2 X 10~^ the gelatin can exist only in the form of gelatin 

 chloride, sulfate, citrate, etc. Water is electrified negatively by such 

 gelatin solutions and hence when pure water is separated by a collodion 

 membrane from a 1 per cent solution of gelatin chloride or sulfate, 

 etc., the water should diffuse more rapidly into the gelatin solution 

 when the anion is monovalent than when it is bivalent. We have 

 shown in a former paper^" that all dibasic and tribasic acids (thus 

 far tried by us), with the exception of sulfuric acid, combine in molec- 

 ular and not equivalent proportions with gelatin. Thus gelatin 

 forms with phosphoric acid a monogelatin phosphate, with tartaric 

 acid a monogelatin tartrate; only with sulfuric acid does it form a 

 digelatin sulfate. In the case of gelatin oxalate it is possible that 

 we have a mixture of both the monogelatin and the digelatin oxalate, 

 the former prevailing. 



This fact is of great importance for our problem. In the case of 

 monogelatin phosphate the anion is not trivalent PO4, but essentially 

 the monovalent anion H2PO4. The same is true for monogelatin 

 citrate and in the case of monogelatin oxalate the anion is not a 

 bivalent oxalate ion but a monovalent oxalate ion with one hydrogen 

 attached. Only in the case of gelatin sulfate is the anion divalent. 

 We have shown in our preceding paper that in the case of NaH2P04 

 the attraction of the salt for water is of the order of magnitude of 

 a salt with monovalent anion like NaCl, showing that the presence 

 of the two H ions weakens the influence of the trivalent PO4 ions 

 considerably. We therefore should expect that in the case of salts 

 like monogelatin citrate, monogelatin phosphate, monogelatin oxalate, 

 and monogelatin tartrate the influence of anion on the rate of the 

 diffusion of water should be of the same order of magnitude as in 

 the case of gelatin chloride or nitrate; while in the case of digelatin 

 sulfate the SO4 ion should act as a divalent anion producing a stronger 

 repelling effect on the negatively charged water than is done by 

 gelatin chloride. This turns out as expected (Fig. 5). 



10 Loeb, J., /. Gen. Physiol., 1918-19, i, 559. 



