110 



THE ROYAL SOCIETY OF CANADA 



In the meantime the tubes A, the rubber stopper and the tubes 

 B were sterilized in boiling water. The hot mixtures of soil and water 

 were then poured into the tube A; the tubes were placed in the centri- 

 fuge cups and the cups were filled with boiling water to the level of 

 the liquid in the tubes A. The centrifuge was then run at top speed 

 for 15 minutes to settle the soil. The centrifuge made 1300 revolu- 

 tions per minute and the middle of the soil columns when settled 

 was 25 cms. from the centre of the axis of the centrifuge. 



The liquid al)ove the settled soil constituents was then emptied 

 out and replaced by a clay subsoil solution, except in the case of the 

 fine clay. In this case the solution was the liquid left above the fine 

 clay when settled. 



The rubber stoppers and tubes B were then inserted and the tubes 

 were placed in a large vessel of distilled water. The level of the dis- 

 tilled water at the beginning was made higher than the level of the 

 liquid in any of the tubes B. 



Daily observations were made on the level of the solutions and 

 the tubes B for a period of 6 weeks. In determining the final osmotic 

 pressure, we made corrections for the height the water rose in the tubes 

 B by surface tension. In the case of the open arm manometer we 

 made corrections for the length of the column of solution in the short 

 arm of the manometers. 



TABLE 2. 



Giving the osmotic pressures, obtained with the different soil constituents used as 



semi-permeatîle meml)ranes. 



These results show that: 



(1) for the solution used the sands do not act as semi-permeable 

 membranes, but the silt, clay and fine clay do so act; 



(2) The finer the soil grains in a soil constituent the greater is 

 the osmotic pressure it suppoits. 



