lOO 



OSMOSIS AND OSMOTIC PRESSURE 



weight molar concentrations. The significance of the last two columns in 

 this table will be discussed later. 



TABLE 14 THE RELATION BETWEEN TEMPERATURE AND THE OSMOTIC PRESSURES OF WEIGHT 



MOLAR SUCROSE SOLUTIONS (dATA OF MORSE, I9I4) 



The data presented in Table 14 show that osmotic pressure increases with 

 increase in temperature. The significance of the last two columns in this 

 table will become apparent in the later discussion. 



TABLE 15 OSMOTIC PRESSURES OF WEIGHT MOLAR SOLUTIONS OF SEVERAL ELECTROLYTES 



AND NON-ELECTROLYTES AS CALCULATED FROM FREEZING POINT DEPRESSIONS (dATA OF 

 JONES, 1907) 



Methyl alcohol 

 Ethyl alcohol 

 NaCl 



22.88 atmos. 



22.51 



42.74 



KNO3 



Ca(N03)2 

 K0CO3 



32. 87 atmos. 



58.88 



52.61 



The important fact illustrated by the data in Table 15 is that while 

 the osmotic pressures of weight molar solutions of non-electrolytes approximate 

 the same value, which is in the neighborhood of van't Hoff's theoretical value 

 (see later) of 22.4 atmospheres, the values for weight molar solutions of 

 electrolytes are much higher. 



Using the results of Pfeffer's classical investigations of osmotic pressure, 

 published in 1877, ^s a basis for his arguments, van't Hofif (1887) showed 

 that a remarkable analogy exists between the osmotic pressures of dilute solu- 

 tions and the pressures exerted by gases. Van't Hoff pointed out that the 

 osmotic pressure of a dilute solution is equal to the pressure that the solute 

 alone would exert were it present as a gas at the same temperature in the 

 same volume as that occupied by the solution. A dilute solution was con- 



