74 



THE ROYAL SOCIETY OF CANADA 

 Table 3. 



Giving the Pressures in centimetres of Water at the beginning and at the 



END OF the Test. 



When tubes are set up with cotton cloth in the regular way the 

 maximum pressure remains constant for months if the water is changed 

 daily and if the temperature remains constant. 



Conclusion. Since in this test the pressure did not increase and 

 did gradually decrease it seems clear that the cause of the usual 

 movement is not colloidal swelling. 



FOURTH TEST. CAN THE MOVEMENT BE REVERSED ? 



If the movement is brought about by osmosis, then it should be 

 possible to reverse the movement by placing the stronger solution 

 outside the tube; this, on trial, proved to be the case. Two tubes 

 were set up as in Fig. 1, with soil solution in the tubes. The following 

 tests were made (1) the tubes were placed in distilled water until 

 some pressure had developed; (2) they were then placed in a soil 

 solution stronger than the solution in the tubes, the pressures fell 

 to zero; (3) they were again placed in distilled water. 



Table 4. 

 Giving the Pressures in centimetres of Water. 



Electrical resistance at 20°C. ; of the solution in tube 1, 1,600 ohms 

 in tube 2, 1,700 ohms; of the strong soil solution 550 ohms; of •02N 

 KCl solution 350 ohms. 



