270 ELECTRIFICATION OF WATER 



IV. 



Gelatin is not the only substance which causes a reversal of the 

 sign of the electrification of the particles of water diffusing through 

 the collodion membrane in the presence of comparatively low con- 

 centrations of acid or of salts with trivalent or tetravalent cations. 

 The same effect can be produced when the collodion membrane is 

 treated with 1 per cent solutions of casein, egg albumin, blood 

 albumin, and edestin; while treatment of the collodion membrane 

 with 1 per cent solutions of Fairchild's peptone, of peptone (pre- 

 pared by Dr. Northrop) from egg albumin digested with pepsin and 

 neutralized, of alanine, of "soluble starch," of "potato starch," and 

 of 0.50 per cent agar-agar did not cause the reversal. The proteins 

 which modify the behavior of the membrane cannot diffuse through 

 the latter but the writer is not yet ready to state that this is the 

 decisive factor. It is of interest that a treatment of the collodion 

 membrane with a 0.002 per cent solution of gelatin makes the 

 membrane already noticeably amphoteric though to a considerably 

 smaller degree than a treatment with a 1 per cent solution of 

 gelatin. 



SUMMARY. 



1. It is shown that collodion membranes which have received one 

 treatment with a 1 per cent gelatin solution show for a long time 

 (if not permanently) afterwards a different osmotic behavior from 

 collodion membranes not treated with gelatin. This difference shows 

 itself only towards solutions of those electrolytes which have a ten- 

 dency to induce a negative electrification of the water particles 

 diffusing through the membrane, namely solutions of acids, acid salts, 

 and of salts with trivalent and tetravalent cations ; while the osmotic 

 behavior of the two types of membranes towards solutions of salts 

 and alkahes, which induce a positive electrification of the water 

 particles diffusing through the membrane, is the same. 



2. When we separate solutions of salts with trivalent cation, e.g. 

 LaCls or AICI3, from pure water by a collodion membrane treated 

 with gelatin, water diffuses rapidly into the solution; while no water 

 diffuses into th*e solution when the collodion membrane has received 

 no gelatin treatment. 



