[lynde] 



UN OSMOSIS IN SOILS. 

 Table III. 



137 



GIVING THE OSMOTIC PRESSURES OBSERVED IN REPEATING THE SECOND EXPERIMENT 



TWICE. 



Duration of first trial, three days. The manometer was accidentally 

 broken. We replaced the manometer and started the experiment 

 again. Duration of second trial, ten days. 



Part II. 



An experiment to determine whether or not the pressure observed is due to swelling 

 of the soil column. 



It occurred to us that the pressures we observed might be due 

 to the swelling of the soil column. To settle this point we prepared 

 soil as above allowing it to settle in water for 4 days. We then set 

 up two tubes as usual and measured the pressure developed. We 

 also set up a third tube in the same way except that we inserted a solid 

 rubber stopper instead of the layer of cotton cloth. Thus no movement 

 of moisture due to osmotic pressure could occur. If then we observed 

 a pressure it could not be due to osmotic pressure but must be due to 

 some other cause such as the swelling of the soil column. 



The two tubes set up in the ordinary way developed osmotic 

 pressures, but less than those given above. 



The third tube with the solid rubber stopper not only did not 

 develop any pressure, but gave a negative pressure. This indicates 

 that the soil solution is absorbed and that the total volume, soil plus 

 solution, decreases. 



We then poured the soil solution out of the tube with the rubber 

 stopper and added distilled water. Again a negative reading was 

 obtained and much greater than with the soil solution. This indicates 

 that the soil column absorbs water more readily than it absorbs soil 

 solution and that there is a greater decrease in total volume. 



Sec. III,il914— 1Q 



