JACQUES LOEB 



263 



MJlUllillllilliiillillinZM 

 4096 2048 1024 512 256 128 64 32 16 6 4 2 



Concentration 



Fig. 5. Negative osmosis when acids (HCl, H2SO4, H3PO4) are separated from 

 water by membranes treated with gelatin. 



Fig. 7 gives the curves for several other acids when the membranes 

 are treated with gelatin and Fig. 8 the curves for the same acids when 

 the membranes are not treated with gelatin. When the membranes 

 are not treated with gelatin the curve for oxalic acid (Fig. 8) becomes 

 almost like that of Na2S04 in Fig. 1 ; while the same acid shows the 

 phenomenon of negative osmosis (Fig. 7) when the membrane has 

 received a gelatin treatment previous to the experiment. 



n. 



What causes this profound difference in the osmotic behavior of 

 collodion membranes according to whether they have or have not 

 received a previous treatment with gelatin? It is so customary in 

 biology to explain obscure phenomena by the assumption of varia- 

 tions of permeability that the writer felt it necessary to test the 

 possibility of such an explanation in this case. 



The phenomenon of positive osmosis for acid when the collodion 

 bag separating the acid from pure water was not treated with gelatin, 

 and the opposite phenomenon of negative osmosis when the collodion 



