464 ELECTRICAL CHARGES AND ANOMALOUS OSMOSIS 



is meant the superposition of electrical forces over the purely osmotic 

 forces in the transport of water through a membrane separating pure 

 water from a solution of an electrolyte (or separating two different 

 solutions of electrolytes). When both water and electrolytes are 

 capable of diffusing through the membrane the difference in the 

 mobility of the oppositely charged ions will cause diffusion potentials 

 acting across the membrane. In this case the solution assumes the 

 opposite sign of charge as the water. These potentials we will call E. 



There may be a second p.d. inside the pores of the membrane be- 

 tween the solid wall of the pore and the liquid inside the pore. This 

 potential we will call e. If as the consequence of e the liquid inside 

 the pore assumes a negative charge, while as a consequence of E the 

 solution in the collodion bag assumes a positive charge, the liquid 

 cylinder inside the pore will be dragged into the solution by these 

 electrical forces and thus an electrical transport of water will be added 

 to the transport of water by osmotic forces. If the solution, however, 

 has the same sign of charge as the liquid inside the pore, the elec- 

 trical force will act in an opposite sense from the osmotic force, and 

 the flow of water from the water side of the membrane into the solu- 

 tion will be less than is to be expected on the basis of van't Hoff 's law. 



This theory of anomalous osmosis was first suggested by Girard^ 

 and has later been supported by Bartell* and others. 



In the experiments to be described salt solutions of a definite pH 

 but of different concentrations were put into collodion flasks of about 

 50 cc. volume, which had received a coating of gelatin as described in 

 previous papers. The collodion bags were dipped into 350 cc. of 

 water of the same pH as that of the salt solution, but containing no 

 salt. The collodion bags were closed with a rubber stopper perforated 

 by a glass tube serving as manometer. The temperature was 24°C. 

 and the rise of the liquid in the manometer was read 20 minutes after 

 the commencement of each experiment. In the close regulation of 



^Girard, P., Compt. rend. Acad., 1908, cxlvi, 927; 1909, cxlviii, 1047, 1186; 

 1910, cl, 1446; 1911, cliii, 401. Girard, P., La pression osmotique et le mechan- 

 isme de Tosmose, Publications de la Societe de Chimie-physique, Paris, 1912. 



^Bartell, F. E., J. Am. Chem. Soc, 1914, xxxvi, 646. Bartell, F. E., and 

 Hocker, C. D., /. Am. Chem. Soc, 1916, xxxviii, 1029, 1036. Bartell, F. E., 

 and Madison, 0. E., J. Physical Chem., 1920, xxiv, 593. 



