JACQUES LOEB 21.5 



containing the same concentration of HNO3 or NaOH respectively. 

 In addition the inside solution {i.e., the solution inside the collodion 

 bag which was connected with the manometer) contained a m/256 

 solution of one of the following four salts: CeCls, CaCU, Li CI, 

 and Na2S04. The ''attraction" of these m:/256 salt solutions 

 for water was therefore tested at different hydrogen ion concentra- 

 tions. It is obvious from Fig. 1 that the "attractive" force of one 

 and the same salt solution for water (measured by the initial rate of 

 diffusion of water from the outside into the salt solution) varied con- 

 siderably with the hydrogen ion concentration of the solution. (The 

 hydrogen ion concentration is expressed by Sorensen's logarithmic 

 symbol pH; i.e., the log of the concentration with the minus sign 

 omitted). The abscissae in the curve are the initial pH of the 

 solutions, while the ordinates are the rise in level of the watery liquid 

 in the glass tubes after 20 minutes at 24°C. 



Fig. 1 shows that somewhere between pH 4.0 and 5.0 a reversal of 

 the sign of charge of the water particles occurs. At pH below 4.0 the 

 water is negatively charged, at pH above 5.0, it is positively charged. 

 This change coincides with a change in the nature of the charge of 

 the gelatin ion. At a pH of 4.0 or below the gelatin forms gelatin 

 nitrate (in the presence of HNO3) iand hence the gelatin ion is a cation. 

 The water, being negative, has the opposite sign of charge as the gela- 

 tin ion. At a pH of 5.0 or above the gelatin forms metal gelatinate, Na 

 gelatinate, Ca gelatinate, etc., and the gelatin ion is negatively charged. 

 The water, being positively charged, has again the opposite charge as 

 the gelatin ion. The exact turning point, the isoelectric point of 

 gelatin, is at a pH 4.7. In a preceding paper^ the writer has been 

 able to show that if other proteins than gelatin are used to give the 

 collodion membrane a coating of a protein, the reversal of the sign 

 of charge of the water varies with the isoelectric point of the protein 

 used. 



If we return to Fig. X we notice that where the water is negatively 

 charged it is "attracted" by the cation of the salt used and " repelled" 

 by the anion with a force increasing with the valency of the ion. The 

 attractive force increases from Li to Ca to Ce, and diminishes from 



^Loeb, J., /. Gen. Physiol., 1919-20, ii, 577. 



