JACQUES LOEB 97 



permanent osmotic pressure of 1 per cent solution of metal gelatinate 

 when the cation is monovalent and bivalent? We have already 

 pubhshed such measurements before we were aware of the fact that 

 the electrification of water might play a role in osmotic pressure. 

 In a paper published in this Journal^ we have shown that when 1 per 

 cent solutions of gelatin salts with monovalent cation — Li, Na, K, 

 and NH4 gelatinate — are separated by collodion membranes from 

 distilled water they may reach a maximal osmotic pressure of from 

 300 to 325 mm. of gelatin solution, while the 1 per cent gelatin solu- 

 tions with bivalent cation — Ca and Ba gelatinate — never reach an 

 osmotic pressure higher than 130 mm.; i.e., a little more than one- 

 third the value of the highest osmotic pressure of 1 per cent solutions 

 of gelatin salts with monovalent cation. 



It seemed desirable to get the time curve for the rise in pressure, 

 since such a curve permits a comparison between the influence of 

 the cation on both the velocity of the diffusion of water from water into 

 solution as well as on the pressure when osmotic equilibrium is reached. 

 The experiment was as follows. The gelatin was rendered isoelectric 

 in a way described in a previous paper. To 1 gm. of isoelectric 

 gelatin were added 20 cc. of 0.01 n of an alkaH (LiOH, NaOH, etc.) 

 and then enough distilled water to bring the solution of the gelatin 

 (which was melted) to 100 cc. The pH of these solutions in the 

 experiment under discussion turned out to be about 8.8. The solu- 

 tions were put into the collodion flasks and the latter were put into 

 beakers containing 350 cc. of H2O, the pH of which was raised at 

 the beginning to about 9.0 by adding 0.2 cc. of 0.01 N NaOH 

 to 350 cc. of H2O, in order to prevent a rapid lowering of the pH of 

 the gelatin solution through the CO2 absorbed from the air by the 

 distilled water of the outside solution. The temperature was 24°C. 

 The pH decreased slowly in the beaker and as a consequence also in 

 the gelatin solution, and in 20 hours the pH had fallen to about 7.0 in 

 the gelatin solutions with monovalent cations, while it had fallen less 

 in the gelatin solutions with bivalent cations. When the pH fell, the 

 osmotic pressure also began to diminish on account of the shifting of 



8 Loeb, J., /. Gen. Physiol, 1918-19, i, 483. 



