Twenty third meeting. 



New York University and Bellcvue Hospital Medical College. May 

 22 y i go J. President Flexner in the chair. 



79 (222) 



The osmotic pressure of colloidal solutions and the influence of 

 electrolytes and non-electrolytes on such pressure. 



By Ralph S. lillie. 



[From the Physiological Laboratory of Johns Hopkins University ■.] 

 Determinations were made of the osmotic pressure of gelatin 

 and egg albumin ; the colloids were used (i) in approximately 

 pure solution, and (2) after the addition of various electrolytes and 

 non-electrolytes to the colloidal solution ; in this case the substance 

 used was added in the same concentration to the outer fluid of the 

 osmometer so as to pervade the entire system on both sides of the 

 membrane in uniform concentration. The osmotic effects observed 

 under these conditions can be due only to the colloid and not to 

 the added substance. The colloidal solution is found, however, 

 after the addition of an acid, alkali, or neutral salt, to exhibit an 

 altered osmotic pressure, the degree of alteration varying with the 

 nature and concentration of the added electrolyte. Non-electro- 

 lytes are found to have no appreciable influence on the osmotic 

 pressure of these colloids. 



The osmometer employed is constructed as follows : The 

 membrane is composed of a moderately thick film of nitro-cellulose 

 (celloidin or gun cotton) and is of the form and capacity of a 50 

 c.C; round bottomed flask ; it is made by coating the interior of 

 such a flask with a thin film of a 10 per cent, solution of celloidin 

 in equal parts of alcohol and ether, and then removing the solvent 

 by evaporation and bathing in hot water. Such membranes are 

 strong and inextensible, readily permeable to crystalloids and 

 water, and (if of the proper thickness) almost impermeable to the 

 above proteids. The manometer is a straight narrow glass tube 

 passing through a rubber stopper which is bound by an elastic 



(in) 



