108 THE ROYAL SOCIETY OF CANADA 



(1) to determine again whether soil acts as a semi-permeable 

 membrane; 



(2) to determine whether its efficiency as a semi-permeable mem- 

 brane increases with the depth of the soil column; 



(3) to measure the total osmotic pressure in each case; 



(4) to find the influence of change of temperature upon the total 

 osmotic pressure obtained in each case. 



The apparatus used is shown in Fig. 3. The experiments were 

 made in duplicate. In two tubes the semi-permeable membrane was 

 6 grams of clay subsoil; in two others, 4 grams, and in the last two, 

 2 grams of clay subsoil. The solution in all was that formed by boiling 

 clay subsoil in distilled water. 



The results showed that, for the clay subsoil used, the following 

 is true: — 



(1) the soil acts as a semi-permeable membrane; 



(2) the efficiency of the soil as a semi-permeable membrane in- 

 creases with the depth of the soil column; 



(3) water moves through the soil towards a solution and develops 

 a certain osmotic pressure; 



(4) the osmotic pressure developed increases with the temperature. 



Experimenis. 



The object of the following experiments, as stated above, was to 

 compare the efficiencies of the different soil constituents as semi- 

 permeable membranes. 



The soil constituents used were as follows: — 

 Table 1, giving the soil constituents used in these experiments. 



Soil constituents Diameter of the grains 



Medium sand -5 .25 m. m. 



Fine sand «25 • 1 



Very fine sand • 1 -Oo 



Silt -05 -005 



Clay -005 -001 



Fine Clay -001 — 



How the soil constituents were obtained. The soil constituents were 

 obtained from different soils from the Macdonald College farm, by the 

 usual operations employed in the mechanical analysis of soils. The 

 sands were obtained from a sandy loan and the silt from a clay loan. 



It will be noticed that there are two clays, which we have called 

 "clay" and "fine clay" respectively. The origin of these clays is as 

 follows. We obtained the "clay" from a clay subsoil, the "fine clay" 

 from a clay loam. We noticed that the "fine clay" was much finer than 



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