OSMOTIC PRESSURE AND GAS PRESSURE 



99 



two sides of the membrane is very considerable the effects of this factor on 

 osmosis are slight, and usually can be disregarded. 



The attainment of an osmotic equilibrium between two solutions, or be- 

 tween a solution and water does not necessarily imply an equalization of 

 solute concentration, nor of pressure, nor of temperature. It does imply, 

 however, an equalization of diffusion pressures and an examination of the 



SUCROSE_ 

 SOLUTION 



V_/ 



SUCROSE 



solution" 



MEMBRANE, 

 i 



Y 



-WATER 



A •■ B 



Fig. 20. Diagrams illustrating discussion of the vapor pressure theory of osmosis. 



circumstances is necessary to determine the exact mechanism by which they 

 have been brought into equilibrium in any given system. 



Analogies between Osmotic Pressure and Gas Pressure, — In Tables 

 13, 14, and 15 are summarized data which illustrate the relations between 

 osmotic pressure and (i) concentration of the solution, (2) temperature, 

 and (3) kind of solute. 



TABLE 13 THE RELATION BETWEEN THE WEIGHT MOLAR CONCENTRATIONS OF SUCROSE 



SOLUTIONS AND THEIR OSMOTIC PRESSURES AT 25° C. (dATA OF MORSE, I9I4) 



Within this range of concentrations, as shown by the data in this table, 

 the osmotic pressures of sucrose solutions are closely proportional to their 



