[lynde-dupré] 



ON OSMOSIS IN SOILS 



73 



lions of the flow were made for a period of two months. At the end 

 of that time the flow was nearly as strong as at the beginning. The 

 observations were discontinued because another test had been started 

 to determine the duration of the flow (see the fifth test). Table 2 

 gives the average daily flow for the first five days and for the last 

 five days of the two months. 



Table 2. 



Giving the Daily Flow, in linear centimetres, at the beginning and at 



THE end of two MONTHS. 



Conclusion (1) A flow is produced. 



(2) It promises to continue for a long time. 



THIRD TEST. IS THE MOVEMENT DUE TO COLLOIDAL SWELLING ? 



We have tried to discover causes, other than osmosis, which 

 might bring about this movement. It occurred to us that possibly 

 the water does not move through the soil but that the colloidal clay 

 absorbs soil solution, swells, and thus produces a movement. 



This did not seem probable in the light of the results obtained 

 in the first and second tests; nevertheless we decided to investigate 

 it as follows: 



Four tubes were set up in the usual way except that solid rubber 

 stoppers were inserted in the bottoms of the tubes in place of the layer 

 of cotton cloth. Thus no movement of water through the soil could 

 take place. If, then, any pressure developed it could not be due to 

 osmosis but must be due to some other cause such as colloidal swelling. 



The four tubes were started with a pressure of about one-half 

 the pressure which might be expected if the tubes were set up in the 

 regular way. No increase in pressure occurred and, on the contrary, 

 the liquid in the measuring tubes fell to zero in two weeks. 



