106 



THE ROYAL SOCIETY OF CANADA 



(1) that with dilute solutions of the same substance, the osmotic 

 pressure is directly proportional to the concentration of the solution. 



(2) that for a given solution, the osmotic pressure increases with 

 the temperature. 



Pfeffer used the apparatus illustrated in Fig. 1. The semi-per- 

 meable membranee was a precipitate of copper ferrocyanide deposited 

 within the walls of an unglazed porcelain cup. The solutions used 

 were chiefly solutions of cane sugar in water. 



The deductions made by van't Hoff and Arrhenius from the results 

 of Pfefifer's work laid the foundation of modern physical chemistry 

 and are familiar to all. 



Os7nosis in Soils. In 1911 while investigating the movement of 

 moisture in soils, I was gradually led to the conclusion that, in producing 

 the movement of moisture in soils, there is some agency at work other 

 than those already known: namely, gravitation, surface tension, and heat. 

 In considering what this agency might be I was led to the following theory. 



Theory that soils act as semi-'permeahle v^emhranes. 



It is possible that: 



(1) soils act as semi-permeable membranes; 



(2) the greater the depth of the soil, the greater is its efficiency 

 as a semi-permeable membrane, up to the point at which it becomes 

 a perfect semi-permeable membrane; 



—A 



,i^ 



-Sugar solution or 



K2SO4 sol. 

 -Cbij subsoil 



-Cotton cloth and 

 Wire gauze 



Figure 2. Modification of Pfeffer's experiment. Clay subsoil is used as the semi- 

 permeable membrane. 



(3) a soil solution moves through the soil by osmotic pressure 

 from points where the solution is less concentrated to points where it 

 is more concentrated. 



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