Permeability 5 
form to that connecting pressure, volume and temperature of a gas, 
namely p v = KT 
Van’t Hoff (1887) further showed that the equation is not merely 
the same but identical with the gas law equation and that if v is 
measured as the volume of one gram-molecule, then K has the same 
value as the gas constant R in the equation 
Pv = RT , 
which in consequence holds also for dilute solutions. 
Fig. 5. Relation between temperature and osmotic pressure of a o'5 weight 
normal solution of sucrose. 
If V is the volume of the solution and n the number of gram 
molecules of solute present in the volume V, the equation becomes 
in consequence PF = nRT 
How near an approximation this is in dilute solutions will appear 
from Figs. 4 and 5. In Fig. 4 is shown in graphical form the relation 
between concentration of solutions of sucose and osmotic pressure 
at constant temperature, and in Fig. 5 is shown the relation between 
